RESUMEN
Nitric oxide (NO), also known as endothelium-derived relaxing factor, is produced by endothelial nitric oxide synthase (eNOS) in the intima and by neuronal nitric oxide synthase (nNOS) in the adventitia of cerebral vessels. It dilates the arteries in response to shear stress, metabolic demands, pterygopalatine ganglion stimulation, and chemoregulation. Subarachnoid haemorrhage (SAH) interrupts this regulation of cerebral blood flow. Hemoglobin, gradually released from erythrocytes in the subarachnoid space destroys nNOS-containing neurons in the conductive arteries. This deprives the arteries of NO, leading to the initiation of delayed vasospasm. But such vessel narrowing increases shear stress, which stimulates eNOS. This mechanism normally would lead to increased production of NO and dilation of arteries. However, a transient eNOS dysfunction evoked by an increase of the endogenous competitive nitric oxide synthase (NOS) inhibitor, asymmetric dimethyl-arginine (ADMA), prevents this vasodilation. eNOS dysfunction has been recently shown to be evoked by increased levels of ADMA in CSF in response to the presence of bilirubin-oxidized fragments (BOXes). A direct cause of the increased ADMA CSF level is most likely decreased ADMA elimination due to the disappearance of ADMA-hydrolyzing enzyme (DDAH II) immunoreactivity in the arteries in spasm. This eNOS dysfunction sustains vasospasm. CSF ADMA levels are closely associated with the degree and time-course of vasospasm; when CSF ADMA levels decrease, vasospasm resolves. Thus, the exogenous delivery of NO, inhibiting the L-arginine-methylating enzyme (IPRMT3) or stimulating DDAH II, may provide new therapeutic modalities to prevent and treat vasospasm. This paper will present results of preclinical studies supporting the NO-based hypothesis of delayed cerebral vasospasm development and its prevention by increased NO availability.
Asunto(s)
Óxido Nítrico Sintasa de Tipo I/metabolismo , Óxido Nítrico Sintasa/metabolismo , Óxido Nítrico/fisiología , Hemorragia Subaracnoidea/complicaciones , Vasoespasmo Intracraneal/etiología , Vasoespasmo Intracraneal/prevención & control , Humanos , Aneurisma Intracraneal/complicaciones , Aneurisma Intracraneal/epidemiología , Donantes de Óxido Nítrico/uso terapéutico , Nitroglicerina/uso terapéutico , Hemorragia Subaracnoidea/epidemiología , Estados Unidos/epidemiología , Vasoespasmo Intracraneal/enzimologíaRESUMEN
BACKGROUND: Cerebrovascular responses to variations in blood pressure and CO2 are attenuated during delayed vasospasm after subarachnoid hemorrhage (SAH). Transcranial Doppler sonography (TCD) is routinely used to assess the presence of vasospasm, but cerebral blood flow velocities (CBF-V) measured by TCD do not necessarily reflect cerebral blood flow (CBF) or the severity of vasospasm. We hypothesized that the correlation of end-tidal pCO2 levels with CBF-V and CBF is equally decreased in subjects with cerebral vasospasm during variations in pCO2. METHODS: Four cynomolgus monkeys were assigned to the vasospasm group and eight animals to the control group. The animals in the vasospasm group underwent placement of an autologous subarachnoid blood clot and vasospasm was confirmed by angiography on day 7. In both groups, CBF and CBF-V were measured simultaneously while end-tidal pCO2 was altered. CBF was measured using a thermal probe placed on the cortical surface and CBF-V was measured using a commercial TCD device. RESULTS: Pearson's correlation coefficient between CBF-V values and pCO2 levels in the control group was strong (r = 0.94, p < 0.001) while it was moderate in the vasospasm group (r = 0.54, p = 0.04). The correlation of CBF values with pCO2 in healthy controls was equally strong (r = 0.87, p = 0.005), while there was no correlation in the vasospasm group (r = -0.09, p = 0.83). CONCLUSION: In this pilot study, correlations of CBF-V with pCO2 values during chemoregulation testing were lower in animals with vasospasm than in healthy ones. This correlation coefficient based on modifications in pCO2 may potentially facilitate the non-invasive assessment of vasospasm.
Asunto(s)
Dióxido de Carbono/metabolismo , Flujometría por Láser-Doppler/métodos , Hemorragia Subaracnoidea/complicaciones , Hemorragia Subaracnoidea/fisiopatología , Vasoespasmo Intracraneal/fisiopatología , Animales , Modelos Animales de Enfermedad , Macaca fascicularis , Proyectos Piloto , Vasoespasmo Intracraneal/etiologíaAsunto(s)
Óxido Nítrico/fisiología , Prolina/análogos & derivados , Vasoespasmo Intracraneal/fisiopatología , Animales , Arginina/uso terapéutico , Astrocitos/fisiología , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Haplorrinos , Humanos , Hidrazinas/farmacología , Peróxido de Hidrógeno/envenenamiento , Óxido Nítrico/uso terapéutico , Donantes de Óxido Nítrico/farmacología , Donantes de Óxido Nítrico/uso terapéutico , Óxido Nítrico Sintasa/metabolismo , Óxidos de Nitrógeno , Oxidantes/envenenamiento , Prolina/uso terapéutico , Ratas , Vasoespasmo Intracraneal/tratamiento farmacológicoRESUMEN
The Janus face of nitric oxide (NO) has prompted a debate as to whether NO plays a deleterious or protective role in tissue injury. There are a number of reactive nitrogen oxide species, such as N2O3 and ONOO-, that can alter critical cellular components under high local concentrations of NO. However, NO can also abate the oxidation chemistry mediated by reactive oxygen species such as H2O2 and O2- that occurs at physiological levels of NO. In addition to the antioxidant chemistry, NO protects against cell death mediated by H2O2, alkylhydroperoxides, and xanthine oxidase. The attenuation of metal/peroxide oxidative chemistry, as well as lipid peroxidation, appears to be the major chemical mechanisms by which NO may limit oxidative injury to mammalian cells. In addition to these chemical and biochemical properties, NO can modulate cellular and physiological processes to limit oxidative injury, limiting processes such as leukocyte adhesion. This review will address these aspects of the chemical biology of this multifaceted free radical and explore the beneficial effect of NO against oxidative stress.
Asunto(s)
Antioxidantes/metabolismo , Óxido Nítrico/metabolismo , Animales , Citotoxicidad Inmunológica , Radicales Libres , Humanos , Peroxidación de Lípido , Estrés Oxidativo/fisiología , Especies Reactivas de Oxígeno/metabolismoRESUMEN
OBJECTIVE: Deleterious effects of strokes may be ameliorated when thrombolysis (i.e., with recombinant tissue plasminogen activator) restores circulation. However, reperfusion injury, mediated by oxygen free radicals (reactive oxygen species [ROS]), may limit the benefits of recombinant tissue plasminogen activator treatment. We hypothesized that, during reperfusion, exogenous nitric oxide (NO) would reduce stroke size by quenching ROS. METHODS: To investigate this hypothesis, we used two in vivo ischemia-reperfusion models, i.e., autologous cerebral embolism in rabbits and filament middle cerebral artery occlusion in rats. Using these models, we measured ROS levels (rabbit model) and stroke volumes (rat model) in response to transient ischemia, with and without intracarotid administration of ultrafast NO donor proline NO (proliNO). RESULTS: In the rabbit cerebral embolism model, intracarotid administration of proliNO (10(-6) mol/L) (n = 6) during reperfusion decreased free radical levels from 538 +/- 86 nmol/L in the vehicle-treated group (n = 7) to 186 +/- 31 nmol/L (2,3'-dihydroxybenzoic acid; P < 0.001) and from 521 +/- 86 nmol/L (n = 7) to 201 +/- 39 nmol/L (2,5'-dihydroxybenzoic acid; P < 0.002). In the rat middle cerebral artery occlusion model, intracarotid administration of proliNO (10(-5) mol/L) (n = 10) during reperfusion reduced the brain infarction volume from 256 +/- 48 mm3 in the vehicle-treated group (n = 8) to 187 +/- 41 mm3 (P < 0.005). In both experimental groups, intracarotid infusion of proliNO did not affect regional cerebral blood flow, mean arterial blood pressure, or brain and body temperatures. CONCLUSION: The beneficial effects of early restoration of cerebral circulation after cerebral ischemia were enhanced by intracarotid infusion of proliNO, most likely because of ROS scavenging by NO. These findings suggest the possibility of preventive treatment of reperfusion injury using NO donors.
Asunto(s)
Infarto de la Arteria Cerebral Media/fisiopatología , Embolia Intracraneal/fisiopatología , Donantes de Óxido Nítrico/farmacología , Óxido Nítrico/farmacología , Prolina/farmacología , Especies Reactivas de Oxígeno/metabolismo , Daño por Reperfusión/fisiopatología , Animales , Encéfalo/irrigación sanguínea , Femenino , Infarto de la Arteria Cerebral Media/patología , Inyecciones Intraarteriales , Embolia Intracraneal/patología , Masculino , Óxidos de Nitrógeno , Prolina/análogos & derivados , Conejos , Flujo Sanguíneo Regional/efectos de los fármacos , Flujo Sanguíneo Regional/fisiología , Daño por Reperfusión/patologíaRESUMEN
OBJECT: Thrombolytic treatments for ischemic stroke can restore circulation, but reperfusion injury, mediated by oxygen free radicals, can limit their utility. The authors hypothesized that, during reperfusion, nitric oxide (NO) provides cytoprotection against oxygen free radical species. METHODS: Levels of NO and oxygen free radicals were determined in both reoxygenation in vitro and reperfusion in vivo models using an NO electrochemical probe and high-performance liquid chromatography with the 2,3- and 2,5-dihydroxybenzoic acid trapping method, before and after addition of the NO donor diethanolamine nitric oxide (DEA/NO). Reoxygenation after anoxia produced a twofold increase in NO release by human fetal astrocytes and cerebral endothelial cells (p < 0.005). In both cell lines, there was also a two- to threefold increase in oxygen free radical production (p < 0.005). In human fetal astrocytes and cerebral endothelial cells given a single dose of DEA/NO, free radical production dropped fivefold compared with peak ischemic levels (p < 0.001). In a study in which a rat global cerebral ischemia model was used, NO production in a vehicle-treated group increased 48 +/- 16% above baseline levels after reperfusion. After intravenous DEA/NO infusion, NO reached 1.6 times the concentration of the postischemic peak in vehicle-treated animals. In vehicle-treated animals during reperfusion, free radical production increased 4.5-fold over basal levels (p < 0.01). After intravenous DEA/NO infusion, free radical production dropped nearly 10-fold compared with peak levels in vehicle-treated animals (p < 0.006). The infarct volume in the vehicle-treated animals was 111 +/- 16.9 mm3; after DEA/NO infusion it was 64.8 +/- 23.4 mm3 (p < 0.01). CONCLUSIONS: The beneficial effect of early restoration of cerebral circulation after cerebral ischemia is limited by reperfusion injury. These results indicate that NO release and oxygen free radical production increase during reperfusion, and suggest a possible early treatment of reperfusion injury using NO donors.
Asunto(s)
Infarto Cerebral/fisiopatología , Óxido Nítrico/fisiología , Especies Reactivas de Oxígeno/metabolismo , Daño por Reperfusión/fisiopatología , Adulto , Animales , Astrocitos/fisiología , Encéfalo/irrigación sanguínea , Línea Celular , Cromatografía Líquida de Alta Presión , Endotelio Vascular/fisiopatología , Feto , Radicales Libres , Humanos , Hipoxia Encefálica/fisiopatología , Técnicas In Vitro , Ratas , Ratas WistarRESUMEN
OBJECT: The use of thrombolytic agents in the treatment of stroke has yielded surprisingly modest success, possibly because of reperfusion injury mediated by reactive oxygen species (ROS). Therefore, scavenging ROS may be of therapeutic value in the treatment of stroke. Nitroxides are low-weight superoxide dismutase mimics, which allows them to act as cell-permeable antioxidants. In this study the nitroxide 4-hydroxy-2,2,6,6,-tetramethylpiperidine-1-oxyl (Tempol) is investigated to determine its ability to reduce reperfusion injury. METHODS: Male Sprague-Dawley rats weighing between 280 g and 350 g underwent middle cerebral artery occlusion with an intraluminal suture for 60 minutes. Regional cerebral blood flow, blood pressure, cerebral temperature, and rectal temperature were monitored during the procedure. After reperfusion, the animals were randomized to groups receiving blinded intravenous administration of either Tempol (10 mg/kg; eight animals) or vehicle (eight animals) over the first 20 minutes of reperfusion (Study I). In a second study to determine dose dependency, animals were randomized to groups receiving Tempol (20 mg/kg; eight animals), low-dose Tempol (5 mg/kg; eight animals), or vehicle (eight animals; Study II). The rats were killed after 4 hours of reperfusion, and brain sections were stained with 2,3,5 triphenyltetrazolium chloride. Infarct volumes were measured using digital imaging. Animals receiving Tempol had significantly reduced infarct volumes at doses of 20 mg/kg and 10 mg/kg compared with controls (49.01+/-18.22% reduction [p = 0.003] and 47.47+/-34.57 [p = 0.02], respectively). No significant differences in the physiological variables measured were observed between groups. CONCLUSIONS: Tempol provides significant neuroprotection after reperfusion in a rat model of transient focal ischemia. These results support the importance of ROS in reperfusion injury and encourage further study of this molecule as a therapeutic agent following thrombolysis.
Asunto(s)
Antioxidantes/uso terapéutico , Óxidos N-Cíclicos/uso terapéutico , Ataque Isquémico Transitorio/complicaciones , Fármacos Neuroprotectores/uso terapéutico , Daño por Reperfusión/prevención & control , Animales , Antioxidantes/administración & dosificación , Presión Sanguínea/efectos de los fármacos , Temperatura Corporal/efectos de los fármacos , Encéfalo/efectos de los fármacos , Infarto Cerebral/patología , Infarto Cerebral/prevención & control , Circulación Cerebrovascular/efectos de los fármacos , Colorantes , Óxidos N-Cíclicos/administración & dosificación , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Depuradores de Radicales Libres/administración & dosificación , Depuradores de Radicales Libres/uso terapéutico , Procesamiento de Imagen Asistido por Computador , Inyecciones Intravenosas , Ataque Isquémico Transitorio/patología , Masculino , Vehículos Farmacéuticos , Distribución Aleatoria , Ratas , Ratas Sprague-Dawley , Especies Reactivas de Oxígeno/metabolismo , Daño por Reperfusión/patología , Método Simple Ciego , Marcadores de Spin , Superóxido Dismutasa/uso terapéutico , Sales de TetrazolioRESUMEN
OBJECT: The reduction in the level of nitric oxide (NO) is a purported mechanism of delayed vasospasm after subarachnoid hemorrhage (SAH). Evidence in support of a causative role for NO includes the disappearance of nitric oxide synthase (NOS) from the adventitia of vessels in spasm, the destruction of NO by hemoglobin released from the clot into the subarachnoid space, and reversal of vasospasm by intracarotid NO. The authors sought to establish whether administration of L-arginine, the substrate of the NO-producing enzyme NOS, would reverse and/or prevent vasospasm in a primate model of SAH. METHODS: The study was composed of two sets of experiments: one in which L-arginine was infused over a brief period into the carotid artery of monkeys with vasospasm, and the other in which L-arginine was intravenously infused into monkeys over a longer period of time starting at onset of SAH. In the short-term infusion experiment, the effect of a 3-minute intracarotid infusion of L-arginine (intracarotid concentration 10(-6) M) on the degree of vasospasm of the right middle cerebral artery (MCA) and on regional cerebral blood flow (rCBF) was examined in five cynomolgus monkeys. In the long-term infusion experiment, the effect of a 14-day intravenous infusion of saline (control group, five animals) or L-arginine (10(-3) M; six animals) on the occurrence and degree of cerebral vasospasm was examined in monkeys. The degree of vasospasm in all experiments was assessed by cerebral arteriography, which was performed preoperatively and on postoperative Days 7 (short and long-term infusion experiments) and 14 (long-term infusion experiment). In the long-term infusion experiment, plasma levels of L-arginine were measured at these times in the monkeys to confirm L-arginine availability. Vasospasm was not affected by the intracarotid infusion of L-arginine (shown by the reduction in the right MCA area on an anteroposterior arteriogram compared with preoperative values). However, intracarotid L-arginine infusion increased rCBF by 21% (p < 0.015; PCO2 38-42 mm Hg) in all vasospastic monkeys compared with rCBF measured during the saline infusions. In the long-term infusion experiment, vasospasm of the right MCA occurred with similar intensity with or without continuous intravenous administration of L-arginine on Day 7 and had resolved by Day 14. The mean plasma L-arginine level increased during infusion from 12.7+/-4 microg/ml on Day 0 to 21.9+/-13.1 microg/ml on Day 7 and was 18.5+/-3.1 microg/ml on Day 14 (p < 0.05). CONCLUSIONS: Brief intracarotid and continuous intravenous infusion of L-arginine did not influence the incidence or degree of cerebral vasospasm. After SAH, intracarotid infusion of L-arginine markedly increased rCBF in a primate model of SAH. These findings discourage the use of L-arginine as a treatment for vasospasm after SAH.
Asunto(s)
Arginina/farmacología , Circulación Cerebrovascular , Óxido Nítrico Sintasa/metabolismo , Hemorragia Subaracnoidea/tratamiento farmacológico , Vasoespasmo Intracraneal/prevención & control , Animales , Arginina/administración & dosificación , Arteria Carótida Interna , Angiografía Cerebral , Modelos Animales de Enfermedad , Infusiones Intraarteriales , Infusiones Intravenosas , Macaca fascicularis , Arteria Cerebral Media/diagnóstico por imagen , Arteria Cerebral Media/efectos de los fármacos , Arteria Cerebral Media/fisiopatología , Distribución Aleatoria , Hemorragia Subaracnoidea/complicaciones , Hemorragia Subaracnoidea/diagnóstico por imagen , Hemorragia Subaracnoidea/fisiopatología , Vasoespasmo Intracraneal/diagnóstico por imagen , Vasoespasmo Intracraneal/etiología , Vasoespasmo Intracraneal/fisiopatologíaRESUMEN
Nitrosative stress can occur when reactive nitric oxide (NO) species compromise the function of biomolecules via formation of NO adducts on critical amine and thiol residues. The capacity of inducible nitric-oxide synthase (iNOS) to generate nitrosative stress was investigated in the murine macrophage line ANA-1. Sequential activation with the cytokines IFN-gamma and either tumor necrosis factor-alpha or interleukin-1beta resulted in the induction of iNOS and production of nitrite (20 nM/min) but failed to elicit nitrosation of extracellular 2,3-diaminonapthalene. Stimulation with IFN-gamma and bacterial lipopolysaccharide increased the relative level of iNOS protein and nitrite production of ANA-1 cells 2-fold; however, a substantial level of NO in the media was also observed, and nitrosation of 2,3-diaminonapthalene was increased greater than 30-fold. Selective scavenger compounds suggested that the salient nitrosating mechanism was the NO/O(2) reaction leading to N(2)O(3) formation. These data mimicked the pattern observed with a 5 microM concentration of the synthetic NO donor (Z)-1-[N-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium -1,2-diolate (PAPA/NO). The NO profiles derived from iNOS can be distinct and depend on the inductive signal cascades. The diverse consequences of NO production in macrophages may reside in the cellular mechanisms that control the ability of iNOS to form N(2)O(3) and elicit nitrosative stress.
Asunto(s)
Macrófagos/metabolismo , Óxido Nítrico Sintasa/biosíntesis , Óxido Nítrico/metabolismo , Animales , Línea Celular , Inducción Enzimática , Interferón gamma/farmacología , Interleucina-1/farmacología , Lipopolisacáridos/farmacología , Ratones , Nitratos/metabolismo , Óxido Nítrico/análisis , Óxido Nítrico Sintasa de Tipo II , Nitritos/metabolismo , Oxihemoglobinas/metabolismo , Factor de Necrosis Tumoral alfa/farmacologíaRESUMEN
Nitric oxide (NO) released from a new chemical class of donors enhances N-methyl-D-aspartate (NMDA) channel activity. Using whole cell and single-channel patch-clamp techniques, we have shown that (Z)-1-[N-(3-ammoniopropyl)-N-(n-propyl)amino]-NO (PAPA-NO) and diethylamine NO, commonly termed NONOates, potentiate the glutamate-mediated response of recombinant rat NMDA receptors (NR1/NR2A) expressed in HEK-293 cells. The overall effect is an increase in both peak and steady-state whole cell currents induced by glutamate. Single-channel studies demonstrate a significant increase in open probability but no change in the mean single-channel open time or mean channel conductance. Reduction in oxygen levels increased and prolonged the PAPA-NO-induced change in both peak and steady-state glutamate currents in transfected HEK cells. PAPA-NO also enhanced cell death in primary cultures of rodent cortical neurons deprived of oxygen and glucose. This potentiation of neuronal injury was blocked by MK-801, indicating a critical involvement of NMDA receptor activation. The NO-induced increase in NMDA channel activity as well as NMDA receptor-mediated cell death provide firm evidence that NO modulates the NMDA channel in a manner consistent with both a physiological role under normoxic conditions and a pathophysiological role under hypoxic conditions.
Asunto(s)
Hipoxia/fisiopatología , Neuronas/fisiología , Óxido Nítrico/fisiología , Receptores de N-Metil-D-Aspartato/fisiología , Animales , Muerte Celular/fisiología , Línea Celular , Conductividad Eléctrica , Ácido Glutámico/fisiología , Humanos , Hidrazinas/farmacología , Hipoxia/patología , Ratones , Ratones Endogámicos , Neuronas/efectos de los fármacos , Neuronas/patología , Óxido Nítrico/farmacología , Óxidos de Nitrógeno , Oxígeno , Presión Parcial , Ratas , Proteínas Recombinantes/metabolismoRESUMEN
Negative sellar exploration (despite the results of endocrine evaluation indicating Cushing's disease), the high incidence of failure of total hypophysectomy, and remission of Cushing's syndrome after unsuccessful hypophysectomy and sellar irradiation suggest that the etiology of refractory Cushing's disease, in some patients, lies near the sella but not in the pituitary gland. We present 5 patients, out of 626 who received surgery for Cushing's disease, in whom an ACTH-secreting extrapituitary parasellar adenoma was identified: 2 after unsuccessful total hypophysectomy for the treatment of refractory Cushing's disease, 2 after unsuccessful hemihypophysectomy (the first, 2 yr before treatment at the NIH for Nelson's syndrome; and the second, with recurrent Cushing's disease 5 yr after negative transsphenoidal exploration), and 1 with a preoperative diagnosis of an intraclival microadenoma, which was cured by resection of the tumor. In all cases, an extrapituitary parasellar microadenoma was confirmed unequivocally as the cause of the disease, by negative pathology of the resected pituitary gland (patients 1, 2, 3, and 5), and/or the remission of the disease after selective resection of the extrasellar adenoma (patients 3, 4, and 5). Three of 5 patients had a partial empty sella. These patients support the thesis that ACTH-secreting tumors can arise exclusively from remnants of Rathke's pouch, rather than from the adenohypophysis (anterior lobe or pars tuberalis of the pituitary gland) and can be a cause of Cushing's disease. In the sixth presented case, an extrapituitary tumor was suspected at surgery after negative pituitary exploration, but serial sections of the hemihypophysectomy specimen revealed a microscopic focus of tumor at the margin of the resected gland. This case demonstrates the importance of negative pituitary histology to establish the presence of an extrapituitary parasellar tumor as an exclusive source of ACTH, and it supports the value of clinical outcome to establish the diagnosis with selective adenomectomy of an extrapituitary parasellar tumor. In patients with negative pituitary magnetic resonance imaging, especially in the presence of a partial empty sella, the diagnostic and surgical approach in Cushing's disease should consider the identification and resection of extrapituitary parasellar adenoma, which can avoid total hypophysectomy, as was possible in 3 of our 5 patients.
Asunto(s)
Adenoma/metabolismo , Hormona Adrenocorticotrópica/metabolismo , Síndrome de Cushing/etiología , Silla Turca , Adenoma/diagnóstico , Adenoma/patología , Hormona Adrenocorticotrópica/sangre , Adulto , Femenino , Humanos , Masculino , Persona de Mediana EdadRESUMEN
UNLABELLED: Hemoglobin released from hemolysed erythrocytes has been postulated to be responsible for delayed cerebral vasospasm after subarachnoid hemorrhage (SAH). However, the evidence is indirect and the mechanisms of action are unclear. Cerebrovascular tone is regulated by a dynamic balance of relaxing and contracting factors. Loss of the endothelium-derived relaxing factor-nitric oxide in the presence of oxyhemoglobin and overproduction of endothelin-1 stimulated by oxyhemoglobin have been postulated as causes of delayed cerebral vasospasm after SAH. OBJECT: The authors aimed to investigate this hypothesis using in vivo microdialysis to examine time-dependent changes in the perivascular concentrations of oxyhemoglobin, deoxyhemoglobin, and methemoglobin in a primate model of SAH. METHODS: Nine cynomolgus monkeys underwent right-sided frontotemporal craniectomy and placement of a semipermeable microdialysis catheter adjacent to the right middle cerebral artery (MCA). Saline (control group, three animals) or an arterial blood clot (SAH group, six animals) was then placed around the MCA and the catheter. Arteriographically confirmed vasospasm had developed in all animals with SAH but in none of the control animals on Day 7. The dialysate was collected daily for 12 days. Levels of oxyhemoglobin, deoxyhemoglobin, and methemoglobin were measured by means of spectrophotometry. Perivascular concentrations of oxyhemoglobin, deoxyhemoglobin, and methemoglobin peaked on Day 2 in the control monkeys and could not be detected on Days 5 to 12. Perivascular concentrations of oxyhemoglobin and deoxyhemoglobin peaked on Day 7 in the SAH group, at which time the concentrations in the dialysate were 100-fold higher than in any sample obtained from the control animals. Methemoglobin levels increased only slightly, peaking between Days 7 and 12, at which time the concentration in the dialysate was 10-fold higher than in samples from the control animals. CONCLUSIONS: This study provides in vivo evidence that the concentrations of oxyhemoglobin and deoxyhemoglobin increase in the cerebral subarachnoid perivascular space during the development of delayed cerebral vasospasm. The results support the hypothesis that oxyhemoglobin is involved in the pathogenesis of delayed cerebral vasospasm after SAH and implicate deoxyhemoglobin as a possible vasospastic agent.
Asunto(s)
Arterias Cerebrales/metabolismo , Hemoglobinas/análisis , Metahemoglobina/análisis , Oxihemoglobinas/análisis , Hemorragia Subaracnoidea/sangre , Análisis de Varianza , Animales , Cateterismo/instrumentación , Angiografía Cerebral , Craneotomía , Modelos Animales de Enfermedad , Endotelina-1/biosíntesis , Exudados y Transudados , Hemólisis , Ataque Isquémico Transitorio/etiología , Ataque Isquémico Transitorio/fisiopatología , Macaca fascicularis , Microdiálisis/instrumentación , Óxido Nítrico/antagonistas & inhibidores , Cloruro de Sodio , Espectrofotometría , Hemorragia Subaracnoidea/complicaciones , Factores de TiempoRESUMEN
OBJECT: Oxyhemoglobin (HbO2) causes vasospasm after subarachnoid hemorrhage (SAH). The most likely spasmogenic component of HbO2 is iron. Various iron chelators, such as deferoxamine, have prevented vasospasm in vivo with limited success. However, only chelators of iron in the ferric state have been studied in animal models of vasospasm after SAH. Because free radical formation requires the ferrous (Fe++) moiety and Fe++ is a potent binder of the vasodilator nitric oxide, the authors hypothesized that iron in the ferrous state causes vasospasm and that chelators of Fe++, such as 2,2'-dipyridyl, may prevent vasospasm. This study was undertaken to investigate the influence of 2,2'-dipyridyl on vasospasm after induction of SAH in a primate model. METHODS: Twelve cynomolgus monkeys were randomly divided into two groups and then both groups underwent placement of an arterial autologous blood clot in the subarachnoid space around the right middle cerebral artery (MCA). The five animals in the control group received intravenously administered saline and the seven treated animals received intravenously administered chelator (2,2'-dipyridyl) for 14 days. Sequential arteriography for assessment of MCA diameter was performed before and on the 7th day after SAH. CONCLUSIONS: Prevention of cerebral vasospasm by means of treatment with continuous intravenous administration of 2,2'-dipyridyl is reported in a primate model of SAH. This result provides insight into the possible mechanism of delayed vasospasm after aneurysmal SAH and provides a potential preventive therapy for it.
Asunto(s)
2,2'-Dipiridil/uso terapéutico , Compuestos Ferrosos/antagonistas & inhibidores , Quelantes del Hierro/uso terapéutico , Ataque Isquémico Transitorio/prevención & control , Hemorragia Subaracnoidea/tratamiento farmacológico , 2,2'-Dipiridil/efectos adversos , Animales , Angiografía Cerebral , Femenino , Inyecciones Intravenosas , Quelantes del Hierro/efectos adversos , Ataque Isquémico Transitorio/diagnóstico por imagen , Hígado/efectos de los fármacos , Hígado/patología , Macaca fascicularis , Masculino , Factores de Tiempo , Transferrina/análisisRESUMEN
Decreased endothelium-derived relaxing factor, nitric oxide (NO), in the arterial wall has been hypothesized to be a potential cause of cerebral vasospasm following subarachnoid hemorrhage (SAH). The authors sought to determine whether intracarotid infusions of newly developed NO-donating compounds (NONOates) could reverse vasospasm or prevent the occurrence of cerebral vasospasm in a primate model of SAH. Twenty-one cynomolgus monkeys were studied in two experimental settings. In an acute infusion experiment, saline or NONOate was infused intracarotidly in four normal monkeys and in four monkeys after onset of SAH. During the infusions regional cerebral blood flow (rCBF) was measured in eight animals and CBF velocity in two. In a chronic infusion experiment, saline (four animals) or NONOate (diethylamine-NO [three animals] or proli-NO [six animals]) was infused intracarotidly in monkeys for 7 days after SAH. In acute infusion experiments, 3-minute intracarotid diethylamine-NO infusions reversed arteriographically confirmed vasospasm of the right middle cerebral artery (MCA) (as viewed on anteroposterior projection, the decrease in area was 8.4+/-4.3% in the treatment group compared with 35+/-12% in the control group; p < 0.004), increased rCBF by 31+/-1.9% (p < 0.002), and decreased the mean systolic CBF velocity in the right MCA. In a long-term infusion experiment, the area of the right MCA in control animals decreased by 63+/-5%. In animals undergoing a 7-day continuous glucantime-NO intracarotid infusion, the area of the right MCA decreased by 15+/-6.2%, and in animals undergoing a 7-day proli-NO infusion, the area of the right MCA decreased by 11+/-2.9% (p < 0.05). The mean arterial blood pressure decreased in the glucantime-NO group from 75+/-12 mm Hg (during saline infusion) to 57+/-10 mm Hg (during glucantime-NO infusion; p < 0.05), but it was unchanged in animals undergoing proli-NO infusion (76+/-12 mm Hg vs. 78+/-12 mm Hg). Results of these experiments show that cerebral vasospasm is both reversed and completely prevented by NO replacement. However, only the use of regional infusion of the NONOate with an extremely short half-life avoided a concomitant decrease in arterial blood pressure, which could produce cerebral ischemia in patients with impaired autoregulation of CBF after the rupture of an intracranial aneurysm.
Asunto(s)
Ataque Isquémico Transitorio/prevención & control , Óxido Nítrico/administración & dosificación , Hemorragia Subaracnoidea/complicaciones , Animales , Arterias Carótidas/diagnóstico por imagen , Angiografía Cerebral , Circulación Cerebrovascular , Modelos Animales de Enfermedad , Femenino , Infusiones Intraarteriales , Ataque Isquémico Transitorio/diagnóstico por imagen , Ataque Isquémico Transitorio/etiología , Ataque Isquémico Transitorio/fisiopatología , Macaca fascicularis , Masculino , Distribución Aleatoria , Hemorragia Subaracnoidea/diagnóstico por imagen , Hemorragia Subaracnoidea/fisiopatologíaRESUMEN
Despite years of research, delayed cerebral vasospasm remains a serious complication of subarachnoid hemorrhage (SAH). Recently, it has been proposed that endothelin-1 (ET-1) mediates vasospasm. The authors examined this hypothesis in a series of experiments. In a primate model of SAH, serial ET-1 levels were measured in samples from the perivascular space by using a microdialysis technique and in cerebrospinal fluid (CSF) and plasma during the development and resolution of delayed vasospasm. To determine whether elevated ET-1 production was a direct cause of vasospasm or acted secondary to ischemia, the authors also measured ET-1 levels in plasma and CSF after transient cerebral ischemia. To elucidate the source of ET-1, they measured its production in cultures of endothelial cells and astrocytes exposed to oxyhemoglobin (10 microM), methemoglobin (10 microM), or hypoxia (11% oxygen). There was no correlation between the perivascular levels of ET-1 and the development of vasospasm or its resolution. Cerebrospinal fluid and plasma levels of ET-1 were not affected by vasospasm (CSF ET-1 levels were 9.3 +/- 2.2 pg/ml and ET-1 plasma levels were 1.2 +/- 0.6 pg/ml) before SAH and remained unchanged when vasospasm developed (7.1 +/- 1.7 pg/ml in CSF and 2.7 +/- 1.5 pg/ml in plasma). Transient cerebral ischemia evoked an increase of ET-1 levels in CSF (1 +/- 0.4 pg/ml at the occlusion vs. 3.1 +/- 0.6 pg/ml 4 hours after reperfusion; p < 0.05), which returned to normal (0.7 +/- 0.3 pg/ml) after 24 hours. Endothelial cells and astrocytes in culture showed inhibition of ET-1 production 6 hours after exposure to hemoglobins. Hypoxia inhibited ET-1 release by endothelial cells at 24 hours (6.4 +/- 0.8 pg/ml vs. 0.1 +/- 0.1 pg/ml, control vs. hypoxic endothelial cells; p < 0.05) and at 48 hours (6.4 +/- 0.6 pg/ml vs. 0 +/- 0.1 pg/ml, control vs. hypoxic endothelial cells; p < 0.05), but in astrocytes hypoxia induced an increase of ET-1 at 6 hours (1.5 +/- 0.6 vs. 6.4 +/- 1.1 pg/ml, control vs. hypoxic astrocytes; p < 0.05). Endothelin-1 is released from astrocytes, but not endothelial cells, during hypoxia and is released from the brain after transient ischemia. There is no relationship between ET-1 and vasospasm in vivo or between ET-1 and oxyhemoglobin, a putative agent of vasospasm, in vitro. The increase in ET-1 levels in CSF after SAH from a ruptured intracranial aneurysm appears to be the result of cerebral ischemia rather than reflecting the cause of cerebral vasospasm.
Asunto(s)
Líquido Cefalorraquídeo/metabolismo , Endotelina-1/metabolismo , Hemorragia Subaracnoidea/metabolismo , Animales , Células Cultivadas , Modelos Animales de Enfermedad , Endotelina-1/líquido cefalorraquídeo , Macaca , MicrodiálisisRESUMEN
To determine the distribution of nitric oxide synthase (NOS) in the primate cerebral artery nervi vasorum and to examine the potential role of NOS in cerebral vasospasm after subarachnoid hemorrhage (SAH) in primates, the distribution of NOS immunoreactivity (NOS-IR) in the major cerebral arteries was examined immunohistochemically in cynomolgus monkeys by the use of whole, mounted preparations of the circle of Willis. In four normal monkeys, NOS-IR was localized to the endothelial and adventitial layers of the large cerebral arteries. On the abluminal side, NOS-IR staining was densely concentrated in perivascular nerve fibers (nervi vasorum) of the anterior circulation. Staining was less prominent in the posterior circulation. In six monkeys with vasospasm on Day 7 after placement of preclotted arterial blood to form an SAH around the right middle cerebral artery (MCA) (42% +/- 8.3% decrease of MCA area, mean +/- standard deviation), NOS-IR was virtually absent in nerve fibers around the spastic right MCA but was normal on the contralateral side. In five monkeys in which vasospasm resolved by Day 14 after SAH (36% +/- 14% decrease of right MCA area on Day 7, and 5% +/- 14% decrease on Day 14), NOS-IR was also absent in the right MCA adventitial nerve fibers and remained normal in the left MCA. Adventitial NOS-IR was also normal in cerebral vessels of a sham-operated, nonspastic monkey. These findings provide further evidence that nitric oxide (NO) functions as a neuronal transmitter to mediate vasodilation in primates and indicate a role for adventitial NO in the pathogenesis of cerebral vasospasm after SAH in humans.
Asunto(s)
Ataque Isquémico Transitorio/enzimología , Óxido Nítrico Sintasa/metabolismo , Análisis de Varianza , Animales , Arterias Cerebrales/metabolismo , Venas Cerebrales/metabolismo , Femenino , Inmunohistoquímica , Ataque Isquémico Transitorio/etiología , Macaca fascicularis , Masculino , Hemorragia Subaracnoidea/complicacionesRESUMEN
The authors sought to develop a model for assessing in vivo regulation of cerebral vasoregulation by nitric oxide (NO), originally described as endothelial-derived relaxing factor, and to use this model to establish the role of NO in the regulation of cerebral blood flow (CBF) in primates. By using regional intraarterial perfusion, the function of NO in cerebral vasoregulation was examined without producing confounding systemic physiological effects. Issues examined were: whether resting vasomotor tone requires NO; whether NO mediates vasodilation during chemoregulation and autoregulation of CBF; and whether there is a relationship between the degree of hypercapnia and hypotension and NO production. Twelve anesthetized (0.5% isoflurane) cynomolgus monkeys were monitored continuously for cortical CBF, PaCO2, and mean arterial pressure (MAP), which were systematically altered to provide control and experimental curves of chemoregulation (CBF vs. PaCO2) and autoregulation (CBF vs. MAP) during continuous intracarotid infusion of 1) saline and 2) an NO synthase inhibitor (NOSI), either L-n-monomethyl arginine or nitro L-arginine. During basal conditions (PaCO2 of 38-42 mm Hg) NOSI infusion of internal carotid artery (ICA) reduced cortical CBF from 62 (saline) to 53 ml/100 g/per minute (p<0.01), although there was no effect on MAP. Increased CBF in response to hypercapnia was completely blocked by ICA NOSI. The difference in regional (r)CBF between ICA saline and NOSI infusion increased linearly with PaCO2 when PaCO2 was greater than 40 mm Hg, indicating a graded relationship of NO production, increasing PaCO2, and increasing CBF. Diminution of CBF with NOSI infusion was reversed by simultaneous ICA infusion of L-arginine, indicating a direct role of NO synthesis in the chemoregulation of CBF. Hypotension and hypertension were induced with trimethaphan camsylate (Arfonad) and phenylephrine at constant PaCO2 (40 +/- 1 mm Hg). Autoregulation in response to changes in MAP from 50 to 140 mm Hg was unaffected by ICA infusion of NOSI. In primates, cerebral vascular tone is modulated in vivo by NO; continuous release of NO is necessary to maintain homeostatic cerebral vasodilation; vasodilation during chemoregulation of CBF is mediated directly by NO production; autoregulatory vasodilation with hypertension is not mediated by NO; and increasing PaCO2 induces increased NO production.
Asunto(s)
Circulación Cerebrovascular/fisiología , Óxido Nítrico/fisiología , Animales , Arginina/análogos & derivados , Arginina/farmacología , Circulación Cerebrovascular/efectos de los fármacos , Homeostasis , Hipercapnia/fisiopatología , Macaca mulatta , Óxido Nítrico Sintasa/antagonistas & inhibidores , Nitroarginina , omega-N-MetilargininaRESUMEN
The pathophysiology of acute neurological complications of diabetic ketoacidosis (DKA) in children and adolescents is not completely understood. We sought to establish whether transcranial Doppler (TCD) was able to monitor the changes of cerebral blood flow regulatory mechanisms, as measured by cerebral blood velocities (CBF-V), Gosling's pulsatility index (PI), and cerebral vascular reactivity (VR), prior to and during treatment of DKA. The increased values of PI suggested an increase of intracranial pressure (ICP) due to the existence of cerebral vasoparalysis, based on the low values of VR prior to treatment and 6 hours after initiation of treatment. At 24 hours, the correction of hematocrit and pH was associated with a significant decrease of PI, suggesting a decrease of ICP, likely due to a return of vascular tone in response to the low PaCO2. This was further supported by an increase of VR in all patients. At 48 hours, when PaCO2 returned to normal, the PI remained low and the VR increased further, suggesting a complete reversal of vasoparalysis and a return of cerebral blood flow regulatory mechanisms.
Asunto(s)
Encéfalo/fisiología , Cetoacidosis Diabética/fisiopatología , Ultrasonografía Doppler Transcraneal , Adolescente , Velocidad del Flujo Sanguíneo , Glucemia/análisis , Presión Sanguínea , Dióxido de Carbono/sangre , Arterias Cerebrales/diagnóstico por imagen , Arterias Cerebrales/fisiopatología , Circulación Cerebrovascular , Niño , Cetoacidosis Diabética/diagnóstico por imagen , Cetoacidosis Diabética/tratamiento farmacológico , Ecoencefalografía , Hematócrito , Hemodinámica , Humanos , Concentración de Iones de Hidrógeno , Presión Intracraneal , Flujo Pulsátil , Resistencia VascularRESUMEN
The continuous release of nitric oxide (NO) is required to maintain basal cerebrovascular tone. Oxyhemoglobin, a putative spasmogen, rapidly binds NO, implicating loss of NO in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH). If vasospasm is mediated by depletion of NO in the vessel wall, it should be reversible by replacement with NO. To investigate this hypothesis, the authors placed blood clots around the right middle cerebral artery (RMCA) of four cynomolgus monkeys; four unoperated animals served as controls. Arteriography was performed before and 7 days after surgery to assess the presence and degree of vasospasm, which was quantified in the anteroposterior (AP) projection by computerized image analysis. On Day 7, cortical cerebral blood flow (CBF) in the distribution of the right MCA was measured during four to six runs in the right internal carotid artery (ICA) of brief infusions of saline followed by NO solution. Arteriography was performed immediately after completing the final NO infusion in three of the four animals with vasospasm. Right MCA blood flow velocities were obtained using transcranial Doppler before, during, and after NO infusion in two vasospastic animals. After ICA NO infusion, arteriographic vasospasm resolved (mean percent of preoperative AP area, 55.9%); that is, the AP areas of the proximal portion of the right MCA returned to their preoperative values (mean 91.4%; range 88%-96%). Compared to ICA saline, during ICA NO infusion CBF increased 7% in control animals and 19% in vasospastic animals (p < 0.002) without significant changes in other physiological parameters. During NO infusion, peak systolic right MCA CBF velocity decreased (130 to 109 cm/sec and 116 to 76 cm/sec) in two vasospastic animals. The effects of ICA NO on CBF and CBF velocity disappeared shortly after terminating NO infusion. Intracarotid infusion of NO in a primate model of vasospasm 1) increases CBF, 2) decreases cerebral vascular resistance, 3) reverses arteriographic vasospasm, and 4) decreases CBF velocity in the vasospastic artery without producing systemic hypotension. These findings indicate the potential for the development of targeted therapy to reverse cerebral vasospasm after SAH.