RESUMEN
1 The molecular mechanism underlying stress-induced hyperglycemia has not been comprehensively clarified. Recently, we demonstrated in ischaemia-reperfusion (I-R) stress-subjected liver that inosine and adenosine are mainly responsible for the hyperglycemia observed. 2 We aimed to advance in the knowledge of the role of inosine plus adenosine as mediators of hepatic-induced hyperglycemia detected after I-R in lower limbs. 3 Acute ischaemia was conducted in anesthetized rats by occluding downstream abdominal aorta and cava vein; then, reperfusion was allowed. Blood samples from hepatic or abdominal cava veins were taken throughout the experiments to measure glucose, inosine and adenosine. Antagonists to adenosine (AdoR) and adrenergic receptors (AdrR) were administered during ischaemia to analyze their effect on hepatic glucose release. 4 Ischaemia up to 60 min produced minor increase of glucose and nucleosides blood values, but 5 min of ischaemia followed by 2- (or 10-) min reperfusion increased glucose 23%, and those of inosine or adenosine by 100%. After 60 min of ischaemia and 10 min of reperfusion, glycemia rose 2-fold and blood inosine and adenosine, 3.3- and 2.7-fold, respectively. A linear positive correlation, r(2), as high as 0.839 between glucose and either nucleoside blood values was calculated. The hyperglycemia response to I-R decreased by 0, 25, 33, 45 and 100% after selective inhibition of A(2B) AdoR, A(2A) AdoR, a(1B) AdrR, A(1) AdoR, and A(3) AdoR, respectively. 5 Inosine-adenosine couple through activation of hepatic A(3) AdoR is the main signal for releasing glucose from liver glycogen and for promoting hyperglycemia following experimental injury of I-R from lower limbs.
Asunto(s)
Adenosina/fisiología , Hiperglucemia/etiología , Inosina/fisiología , Receptor de Adenosina A3/fisiología , Daño por Reperfusión/metabolismo , Adenosina/sangre , Antagonistas del Receptor de Adenosina A3 , Adenosina Trifosfato/metabolismo , Animales , Glucemia/análisis , Extremidades/irrigación sanguínea , Glucosa/metabolismo , Inosina/sangre , Hígado/metabolismo , Masculino , Ratas , Ratas WistarAsunto(s)
Antiinflamatorios no Esteroideos/farmacocinética , Antioxidantes/farmacocinética , Pollos/metabolismo , Piroxicam/farmacocinética , Administración Oral , Animales , Antiinflamatorios no Esteroideos/administración & dosificación , Antioxidantes/administración & dosificación , Relación Dosis-Respuesta a Droga , Hígado/metabolismo , Pulmón/metabolismo , Miocardio/metabolismo , Piroxicam/administración & dosificación , Distribución Aleatoria , Sustancias Reactivas al Ácido Tiobarbitúrico/metabolismoRESUMEN
Nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most employed therapeutic agents. They have a wide spectrum of biological effects, some of which are independent of cyclooxygenase inhibition, such as the alterations on the components of signal transduction systems. In particular, previous data from our laboratory suggested an antagonism between epinephrine and piroxicam, one of the most prescribed NSAIDs. Thus, this study deals with the epinephrine-piroxicam antagonism recorded for metabolic responses in isolated rat hepatocytes. The obtained results show that epinephrine stimulates lactate and ethanol consumption, stimulates glucose release from lactate only, and has no effect on cellular triacylglycerides content. Otherwise, in a dose-dependent basis, piroxicam stimulates lactate and ethanol consumption accompanied by an increase in triacylglycerides content, without changes in glucose release by hepatocytes. Piroxicam blocks the epinephrine-induced stimulation of glucose release from lactate, and epinephrine blocks the piroxicam-mediated increase in triacylglycerides content from lactate or ethanol. In contrast, the effects of epinephrine and piroxicam, promoting the consumption of lactate and ethanol, are not antagonized or added after the simultaneous administration of both compounds. This last result is probably related to the ability of both compounds to stimulate oxygen consumption. On isolated rat liver mitochondria, micromolar doses of piroxicam partially uncouple oxidative phosphorylation, and paradoxically stimulates an ATP-dependent mitochondrial function as citrullinogenesis. These results show for first time, on isolated rat hepatocytes, an antagonism between the metabolic responses of epinephrine and piroxicam, at the concentration found in plasma after its therapeutical administration.
Asunto(s)
Antiinflamatorios no Esteroideos/farmacología , Epinefrina/farmacología , Hígado/efectos de los fármacos , Piroxicam/farmacología , Adenosina Difosfato/farmacología , Animales , Relación Dosis-Respuesta a Droga , Interacciones Farmacológicas , Etanol/metabolismo , Glucosa/metabolismo , Ácido Láctico/metabolismo , Hígado/citología , Hígado/metabolismo , Masculino , Mitocondrias Hepáticas/efectos de los fármacos , Mitocondrias Hepáticas/metabolismo , Consumo de Oxígeno/efectos de los fármacos , Ratas , Ratas Wistar , Triglicéridos/metabolismoRESUMEN
The effect of three different receptor-specific adenosine agonists on the rate of ureagenesis by isolated rat hepatocytes and the dependence on the external free Ca2+ concentration ([Ca2+]e) were investigated. In the presence of high [Ca2+]e all adenosine receptor agonists increased ureagenesis to similar levels. However, with low [Ca2+]e the effects of each agonist varied as follows: (i) the adenosine A1 receptor agonist, 2-chloro-N6-cyclopentyl-adenosine, increased ureagenesis depending partially on [Ca2+]e, (ii) the adenosine receptor A2 agonist, 2-p-(-2-carboxy-ethyl) phenethylamino-5'-N-ethylcarboxyamido adenosine hydrochloride, increased ureagenesis independently of [Ca2+]e and (iii) in contrast, the adenosine receptor A3 agonist N6-2-(-4-aminophenyl) ethyladenosine, increased ureagenesis only in the presence of high [Ca2+]e. The adenosine receptor A1 antagonist, 1-allyl-3,7-dimethyl-8-phenyl xanthine, inhibited the effect of the adenosine receptor A1 agonist on ureagenesis, but not the effect of the adenosine A2 or A3 receptor agonists. The adenosine A2 receptor antagonist, 3,7-dimethyl-1-propargylxanthine, inhibited only the effect of the adenosine A2 receptor agonist. Thus, in addition to A1 and A2 type adenosine receptors, rat hepatocytes possess an A3-like adenosine receptor which responds to the addition of an adenosine A3 agonist by accelerating ureagenesis a [Ca2+]e dependent manner. Moreover, it was observed that in the presence of extracellular Ca2+ each agonist increased [Ca2+]i and this effect was inhibited by the appropriate specific antagonist.
Asunto(s)
Calcio/fisiología , Hígado/metabolismo , Receptores Purinérgicos P1/metabolismo , Animales , Células Cultivadas , Citoplasma/efectos de los fármacos , Citoplasma/metabolismo , Cinética , Hígado/citología , Masculino , Agonistas del Receptor Purinérgico P1 , Antagonistas de Receptores Purinérgicos P1 , Ratas , Ratas Wistar , Transducción de Señal/efectos de los fármacos , Urea/metabolismoRESUMEN
It has been reported that piroxicam prevents the hepatic increase of triacylglycerides and thiobarbituric acid-reactive substances observed after acute ethanol intoxication in rats and also causes a decrease in blood ethanol concentration. The aim of this study was to assess the effect of piroxicam on these 3 metabolic indicators, using isolated rat hepatocytes incubated with ethanol or lactate, supplemented or not with epinephrine. Epinephrine stimulated the consumption of lactate, but not of ethanol. In the isolated hepatocytes, and in a dose-dependent fashion, piroxicam alone raised the consumption of lactate and ethanol, increased the triacylglyceride pool in cells incubated with lactate or ethanol, and decreased the content of thiobarbituric acid-reactive substances in cells incubated with ethanol, but not with lactate. Epinephrine blocked these actions of piroxicam, except the lowering of the content of thiobarbituric acid-reactive substances. Thus, piroxicam helps to control the oxidative stress produced in isolated hepatocytes by ethanol.
Asunto(s)
Antiinflamatorios no Esteroideos/farmacología , Etanol/farmacología , Hígado/citología , Piroxicam/farmacología , Animales , Epinefrina/fisiología , Etanol/metabolismo , Ácido Láctico/metabolismo , Hígado/efectos de los fármacos , Hígado/metabolismo , Masculino , Ratas , Ratas Wistar , Sustancias Reactivas al Ácido Tiobarbitúrico/metabolismoRESUMEN
The objective of this study was to evaluate the gluconeogenic response of in vitro stimulated hepatocytes from control broilers and broilers with clinical manifestations of the ascites syndrome. The basal rate of glucose synthesis from lactate was found to be threefold greater in sick birds than in the control group and stimulation obtained with epinephrine was found to be quantitatively similar in both groups. Under basal conditions, the hepatocytes from the sick broilers exhibited 60% more ammonium than the control birds. In addition, the quantification of thiobarbituric acid reactive substances, as indicators of cellular lipoperoxidation, showed an increase of over 100% in heart and liver of sick broilers fowl. In conclusion, the complex integrated response of gluconeogenesis to epinephrine is maintained in broilers with ascites, although their hepatocytes present changes compatible with those observed in cases of oxidative stress. It is not known whether this stress is a cause or a consequence of the ascites syndrome.
Asunto(s)
Ascitis/veterinaria , Pollos/metabolismo , Hígado/metabolismo , Miocardio/metabolismo , Estrés Oxidativo/fisiología , Enfermedades de las Aves de Corral/metabolismo , Adenosina/farmacología , Animales , Ascitis/metabolismo , Ascitis/fisiopatología , Pollos/fisiología , Epinefrina/farmacología , Radicales Libres/metabolismo , Glucagón/farmacología , Glucosa/metabolismo , Corazón/fisiología , Lactatos/metabolismo , Peroxidación de Lípido , Hígado/química , Hígado/fisiología , Malondialdehído/análisis , Malondialdehído/metabolismo , Miocardio/química , Enfermedades de las Aves de Corral/fisiopatología , Compuestos de Amonio Cuaternario/análisis , Compuestos de Amonio Cuaternario/metabolismo , Síndrome , Sustancias Reactivas al Ácido Tiobarbitúrico/análisis , Sustancias Reactivas al Ácido Tiobarbitúrico/metabolismoRESUMEN
Isolated rat hepatocytes, incubated in a high K+ medium which depolarizes their plasma membrane, were used to investigate the response to adenosine. High K+ concentration blocked both the adenosine mediated increase of calcium influx and the increase in the rate of urea synthesis. It is concluded that a) adenosine stimulates calcium influx in hepatocytes probably through receptor-operated Ca2+ channels which are closed by depolarization of the plasma membrane, b) the higher cytosolic calcium concentration triggers a regulatory step that fully stimulates the rate in urea synthesis.
Asunto(s)
Adenosina/farmacología , Canales de Calcio/efectos de los fármacos , Calcio/metabolismo , Hígado/metabolismo , Potasio/farmacología , Animales , Citosol/metabolismo , Relación Dosis-Respuesta a Droga , Hígado/citología , Masculino , Ratas , Ratas Wistar , Urea/metabolismoRESUMEN
The role of cyclic-adenosine monophosphate (cAMP) and calcium (Ca2+) in the metabolic responses to adenosine was studied in isolated hepatocytes from fed rats. In the presence of 1.2 mM Ca but not in the absence of Ca2+, adenosine stimulated ureagenesis without increasing cAMP. Adenosine inhibited the glucagon mediated increase in cAMP. Adenosine increased free cytoplasmic Ca2+ provided that cells were incubated in the presence of external Ca2+. In the absence of added Ca2+ adenosine did not stimulate ureagenesis or the movements of Ca2+. It is suggested that, in the liver cell, Ca2+ may be a second messenger for adenosine.
Asunto(s)
Adenosina/farmacología , Calcio/farmacología , Hígado/metabolismo , Animales , Calcio/metabolismo , AMP Cíclico/metabolismo , Epinefrina/farmacología , Glucagón/farmacología , Hígado/citología , Hígado/efectos de los fármacos , Masculino , Ratas , Ratas Endogámicas , Espectrometría de Fluorescencia , Urea/metabolismoRESUMEN
In isolated rat hepatocytes adenosine and inosine showed a dose-dependent increase in the rate of glucose synthesis from lactate with a Ka of 7.5 x 10(-8) and 9 x 10(-8) M, respectively. Absence of this action was recorded with: IMP, xanthosine, adenine, hypoxanthine, and uric acid. A reciprocal inhibition of individual gluconeogenic stimulation was found in cells incubated with glucagon or epinephrine and adenosine, but not with inosine. 5'-(N-ethyl) carboxamido adenosine was more potent than adenosine, whereas N6-(L-2-phenylisopropyl)-adenosine antagonized the stimulation of gluconeogenesis by adenosine. Neither of the analogs used modified the stimulatory role of inosine on the studied pathway. Adenosine and inosine may be involved in the short term regulation of gluconeogenesis.
Asunto(s)
Adenosina/farmacología , Gluconeogénesis/efectos de los fármacos , Inosina/farmacología , Lactatos/metabolismo , Hígado/metabolismo , Animales , Epinefrina/farmacología , Glucagón/farmacología , Técnicas In Vitro , Hígado/citología , Masculino , Ratas , Ratas EndogámicasRESUMEN
Adenosine and inosine produced a dose-dependent stimulation of ureagenesis in isolated rat hepatocytes. Hypoxanthine, xanthine and uric acid were without effect. Half-maximally effective concentrations were 0.08 microM for adenosine and 5 microM for inosine. Activation of ureagenesis by both nucleosides had the following characteristics: (a) it was observed with either glutamine or (NH4)2CO3, provided that glucose was present; (b) it was not detected when glucose was replaced by lactate plus oleate; (c) it was mutually antagonized by glucagon, but not by adrenaline; and (d) it was dependent on Ca2+. We suggest that the action of adenosine and inosine on ureagenesis might be of physiological significance.