RESUMEN
Glutamate can induce neuronal cell death by activating ionotropic glutamate receptors (iGluRs) as well as metabotropic glutamate receptors (mGluRs). In the present study, we investigated whether glutamate induces apoptosis of cultured anterior pituitary cells from female rats. Glutamate (1 mm) significantly reduced the metabolic activity of viable cells and increased the percentage of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL)-positive cells and caspase-3 activity in anterior pituitary cells. The inhibitory effect of glutamate on the viability of anterior pituitary cells was not observed in the presence of [2S]-alpha-ethylglutamic acid (0.75 mm), a specific group II mGluR antagonist. Also, (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine (LCCG-I; 0.75 mm), a specific group II mGluR agonist, reduced viability and increased the percentage of TUNEL-positive anterior pituitary cells. Group I and III mGluRs and iGluRs agonists failed to modify the metabolic activity of anterior pituitary cells. Glutamate and LCCG-I increased the percentage of TUNEL-positive lactotropes and somatotropes. The subunit mGluR2/3, belonging to group II mGluR, was localized in these cell types. Glutamate increased nitric oxide (NO) synthase (NOS) activity and inducible NOS expression in anterior pituitary cells. N-methyl-l-arginine (NMMA, 0.5 mm), a NOS inhibitor, potentiated the apoptotic effect of glutamate in anterior pituitary cells, indicating that NO may restrain glutamate-induced apoptosis. Incubation of anterior pituitary cells with a cAMP analog (N6, 2'-o-dibutyryladenosine 3', 5'-cyclic monophosphate; 1 mm) attenuated the apoptosis induced by glutamate. Glutamate and LCCG-I decreased prolactin release from anterior pituitary cells. N6, 2'-o-dibutyryladenosine 3', 5'-cyclic monophosphate reversed the inhibitory effect of glutamate on prolactin release, but NMMA failed to modify it. Our data show that glutamate induces apoptosis of lactotropes and somatotropes through group II mGluR activation, probably by decreasing cAMP synthesis.
Asunto(s)
Apoptosis/efectos de los fármacos , Ácido Glutámico/farmacología , Adenohipófisis/fisiología , Receptores de Glutamato Metabotrópico/fisiología , Animales , Células Cultivadas , AMP Cíclico/fisiología , Femenino , Expresión Génica , Óxido Nítrico/fisiología , Óxido Nítrico Sintasa/genética , Óxido Nítrico Sintasa/metabolismo , Adenohipófisis/citología , Adenohipófisis/metabolismo , Prolactina/metabolismo , Ratas , Ratas Wistar , Receptores de Glutamato Metabotrópico/metabolismo , Distribución TisularRESUMEN
Although the presence of ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptors has been demonstrated in the anterior pituitary, recent reports on the direct effect of glutamate on prolactin (PRL) secretion by anterior pituitary cells have presented contradictory results. Hence, the aim of this study was to determine the effect of ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptor agonists on prolactin (PRL) release. In addition, since D-Aspartate (D-Asp) is found in the pituitary and is involved in neuroendocrine regulation, we also studied the direct action of D-Asp on PRL secretion. Finally, since the posterior pituitary participates in the regulation of PRL secretion, we examined the influence of the posterior pituitary on the effects of NMDA and D-Asp on PRL release. Glutamate (1000 microM) increased PRL secretion from cultured anterior pituitary cells. Both NMDA (100 microM) and kainate (100 microM) increased PRL secretion and these effects were blocked by a specific NMDA receptor antagonist. AMPA did not modify PRL release in these cultures. The group I and II mGluR agonist, trans-ACPD (1000 microM), and a specific group II mGluR agonist, L-CCG-I (100-1000 microM), inhibited whereas specific group I and III mGluR agonists, 3-HPG and L-AP4 respectively, had no effect on PRL release. Finally, D-Asp (100-1000 microM) stimulated PRL secretion and this effect was reduced by a NMDA receptor antagonist. When anterior pituitary cells were cultured in the presence of posterior pituitary cells, NMDA did not modify PRL or GABA release, while D-Asp increased PRL secretion and decreased GABA release in these cocultures. In conclusion, our results show that L-glutamate has a differential direct effect on PRL release: it exerts a stimulatory action via iGluRs and an inhibitory effect via mGluRs. D-Asp could directly stimulate PRL release through NMDA receptors. D-Asp may also stimulate PRL release by decreasing GABA release from the posterior pituitary.
Asunto(s)
Ácido Aspártico/farmacología , Agonistas de Aminoácidos Excitadores/farmacología , Adenohipófisis/metabolismo , Prolactina/metabolismo , Receptores de Glutamato/fisiología , Receptores de Glutamato Metabotrópico/fisiología , Animales , Células Cultivadas , AMP Cíclico/metabolismo , Cicloleucina/análogos & derivados , Cicloleucina/farmacología , Femenino , Adenohipófisis/efectos de los fármacos , Quinoxalinas/farmacología , Ratas , Ratas Wistar , Receptores de Glutamato/efectos de los fármacosRESUMEN
The effects of Wallerian degeneration of the peripheral sympathetic neurons projecting to the hypothalamus on the mechanism of interaction between prolactin and substance P (SP) were examined. The effects of superior cervical ganglionectomy (SCGx) on SP content in various hypothalamic regions and in the hypophysis were evaluated in control and hyperprolactinemic rats. Male rats that received pituitary transplants at the age of 5 days and age-matched sham-operated controls were used. Pituitary grafting significantly increased circulating values of prolactin, as did SCGx. In hyperprolactinemic rats, SCGx partially decreased plasma prolactin levels. Neonatal hyperprolactinemia decreased SP content in the anterior (AH) and posterior (PH) hypothalamus and in the median eminence (ME), but increased it in the mediobasal hypothalamus (MBH). Acute SCGx significantly increased SP in the MBH, PH, and ME. SCGx in hyperprolactinemic animals further increased SP content in MBH. In the ME and Ah, SCGx in pituitary grafted rats decreased SP content as compared with the controls. In the pituitary gland (PG), SCGx only decreased SP content in hyperprolactinemic, but not in control rats. An interaction between peripheral nor-adrenergic neurons and prolactin to regulate SP within the hypothalamus was positive in the MBH, AH, ME, and PG, but not in the PH. These data indicate the existence of interactive mechanisms between prolactin and the peripheral sympathetic neurons to regulate SP content at the hypothalamic-pituitary axis. Interrelationships between prolactin and SP were also observed.
Asunto(s)
Hiperprolactinemia/metabolismo , Hipotálamo/metabolismo , Hipófisis/metabolismo , Sustancia P/metabolismo , Sistema Nervioso Simpático/metabolismo , Degeneración Walleriana/metabolismo , Animales , Ganglionectomía , Hipotálamo Anterior/metabolismo , Hipotálamo Posterior/metabolismo , Masculino , Neuronas/metabolismo , Prolactina/sangre , Ratas , Ratas Wistar , Ganglio Cervical SuperiorRESUMEN
Nitric oxide (NO) affects cyclooxygenase (COX) and lipooxygenase (LOX) activities in several tissues. The aim of this study was to investigate the effect of NO on the AA metabolism in the anterior pituitary. LOX and COX products from anterior pituitaries of Wistar male rats were determined by [14C]-AA radioconversion method. Sodium nitroprusside (NP, 0.5 mM) and DETA NONOate (1 mM), NO donors, decreased 5-hydroxy-5,8,11,14-eicosatetraenoic acid (5-HETE) synthesis (P<0.05), effects that were reversed by hemoglobin. L-arginine also inhibited LOX activity. To the contrary, the inhibition of NO synthase by L-NAME (0.5 mM) or aminoguanidine (0.5 mM) increased 5-HETE production (P<0.05). COX activity was slightly stimulated by NP and L-arginine. However, DETA NONOate induced a stimulation of the synthesis of all prostanoids (P<0.05), this effect being reversed by hemoglobin. Neither NOS inhibitors nor hemoglobin modified basal prostanoids synthesis. These results indicate that NO inhibits LOX activity and stimulates COX activity in the anterior pituitary gland. The inhibition of LOX by NO may be another mechanism involved in the effects of NO on hormone release in the anterior pituitary.
Asunto(s)
Ácido Araquidónico/metabolismo , Óxido Nítrico/fisiología , Adenohipófisis/metabolismo , Animales , Relación Dosis-Respuesta a Droga , Depuradores de Radicales Libres/farmacología , Ácidos Hidroxieicosatetraenoicos/biosíntesis , Lipooxigenasa/efectos de los fármacos , Lipooxigenasa/metabolismo , Masculino , Óxido Nítrico/farmacología , Prostaglandina-Endoperóxido Sintasas/efectos de los fármacos , Prostaglandina-Endoperóxido Sintasas/metabolismo , Ratas , Ratas WistarRESUMEN
In order to determine whether ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptor activation modulates oxytocin release in male rats, we investigated the effect of agonists of both types of glutamate receptors on oxytocin release from hypothalamus and posterior pituitary. Kainate and quisqualate (1 mM) increased hypothalamic oxytocin release. Their effects were prevented by selective AMPA/kainate receptor antagonists. NMDA (0.01-1 mM) did not modify hypothalamic oxytocin release. Group I mGluR agonists, such as quisqualate and 3-HPG, significantly increased hypothalamic oxytocin release. These effects were blocked by AIDA (a selective antagonist of group I mGluRs). In the posterior pituitary, oxytocin release was not modified by kainate, quisqualate, trans-ACPD (a broad-spectrum mGluR agonist) and L-SOP (a group III mGluR agonist). However, NMDA (0.1 mM) significantly decreased oxytocin release from posterior pituitary. D-Aspartate significantly increased oxytocin release from the hypothalamus, while it decreased oxytocin release from posterior pituitary. AP-5 (a specific NMDA receptor antagonist) reduced the D-Aspartate effect in the hypothalamus, but not in the posterior pituitary. Our data indicate that the activation of non-NMDA receptors and group I mGluRs stimulates oxytocin release from hypothalamic nuclei, whereas NMDA inhibits oxytocinergic terminals in the posterior pituitary. D-Aspartate also has a dual effect on oxytocin release: stimulatory at the hypothalamus and inhibitory at the posterior pituitary. These results suggest that excitatory amino acids differentially modulate the secretion of oxytocin at the hypothalamic and posterior pituitary levels.
Asunto(s)
Ácido Aspártico/farmacología , Agonistas de Aminoácidos Excitadores/farmacología , Hipotálamo/metabolismo , Oxitocina/metabolismo , Neurohipófisis/metabolismo , Animales , Hipotálamo/efectos de los fármacos , Técnicas In Vitro , Masculino , Neurohipófisis/efectos de los fármacos , Ratas , Ratas Wistar , Receptores AMPA/agonistas , Receptores de Glutamato Metabotrópico/metabolismo , Receptores de N-Metil-D-Aspartato/antagonistas & inhibidoresRESUMEN
Neurokinin A (NKA) is a tachykinin that participates in the control of neuroendocrine functions. The posterior pituitary lobe (PP) contains abundant nitric oxide synthase (NOS), suggesting that nitric oxide (NO) may play a role in controlling the release of neuropeptides and neurotransmitters. In the present project, we investigated the in vitro effect of NKA on oxytocin release from hypothalamic explants and PP of male rats and the possible involvement of NO in the action of NKA. Since NKA inhibits gamma-aminobutyric acid (GABA) release from PP, we also examined the role of NO in the effect of NKA on basal and K(+)-evoked GABA release. NKA (10(-7)-10(-5) M) significantly decreased oxytocin release from PP, whereas it did not affect its release from hypothalamic explants. The inhibitory effect of NKA on oxytocin release from PP was completely blocked by the NOS inhibitors N(G)-monomethyl-L-arginine (L-NMMA, 0.5 mM) or N(G)-nitro-L-arginine-methyl-ester (L-NAME, 1 mM). Sodium nitroprusside (0.5 mM), an NO releaser, had no effect on basal GABA release but significantly decreased K(+)-evoked GABA release. L-NMMA (0.3 mM) and L-NAME (0.5 mM) increased K(+)-evoked GABA release, indicating that NO plays an inhibitory role in GABA release from PP. The inhibition in both basal and K(+)-evoked GABA release induced by NKA (10(-7) M) was reduced by L-NAME (1 mM). Also, NKA (10(-7) M) increased NO synthesis as measured by [(14)C] citrulline production. Considered all together, our data indicate that NO may mediate the inhibitory effect of NKA on the release of both oxytocin and GABA from PP.
Asunto(s)
GMP Cíclico/análogos & derivados , Neuroquinina A/farmacología , Óxido Nítrico Sintasa/efectos de los fármacos , Oxitocina/efectos de los fármacos , Neurohipófisis/efectos de los fármacos , Ácido gamma-Aminobutírico/efectos de los fármacos , Animales , GMP Cíclico/farmacología , Relación Dosis-Respuesta a Droga , Inhibidores Enzimáticos/farmacología , Hipotálamo/efectos de los fármacos , Hipotálamo/metabolismo , Técnicas In Vitro , Masculino , NG-Nitroarginina Metil Éster/farmacología , Óxido Nítrico/fisiología , Óxido Nítrico Sintasa/metabolismo , Oxitocina/metabolismo , Neurohipófisis/metabolismo , Potasio/farmacología , Ratas , Ratas Wistar , Tionucleótidos/farmacología , Ácido gamma-Aminobutírico/metabolismo , omega-N-Metilarginina/farmacologíaRESUMEN
Considering that tumor necrosis factor-alpha (TNF-alpha) is involved in normal tissue homeostasis and that its receptors are expressed in the anterior pituitary, we examined the effect of this cytokine on pituitary cell growth. Because anterior pituitary function depends on hormonal environment, we also investigated the influence of gonadal steroids in the effects of TNF-alpha on cell proliferation and the release of PRL from anterior pituitary cells. In addition, the release of TNF-alpha and its action on the release of PRL from anterior pituitary cells of rats at different stages of the estrous cycle was evaluated. In minimum essential medium D-valine, a medium that restricts fibroblastic proliferation, TNF-alpha (10 and 50 ng/mL) reduced 3H-Thymidine incorporation, DNA content, and active cell number. TNF-alpha failed to affect proliferation of cells from ovariectomized (OVX) rats. However, it significantly inhibited growth of cells from OVX rats cultured with 17beta-estradiol (E2) (10(-9) M) and from chronically estrogenized rats. TNF-alpha decreased the release of PRL from cells of intact rats, especially in proestrous, OVX rats cultured with E2 and chronically estrogenized rats. The release of anterior pituitary TNF-alpha was higher in proestrous rats. These results indicate that TNF-alpha plays an inhibitory role in anterior pituitary cell growth and the release of PRL in an estrogen-dependent manner.
Asunto(s)
División Celular/efectos de los fármacos , Estrógenos/farmacología , Adenohipófisis/citología , Adenohipófisis/metabolismo , Prolactina/metabolismo , Factor de Necrosis Tumoral alfa/farmacología , Animales , Células Cultivadas , ADN/biosíntesis , Estradiol/farmacología , Estrógenos/fisiología , Estro , Femenino , Fibroblastos/citología , Interleucina-6/farmacología , Ovariectomía , Adenohipófisis/efectos de los fármacos , Ratas , Ratas Wistar , Factor de Necrosis Tumoral alfa/metabolismoRESUMEN
Substance P (SP) may participate as a paracrine and/or autocrine factor in the regulation of anterior pituitary function. This project studied the effect of TRH on SP content and release from anterior pituitary and the role of SP in TRH-induced prolactin release. TRH (10(-7) M), but not vasoactive intestinal polypeptide (VIP), increased immunoreactive-SP (ir-SP) content and release from male rat anterior pituitary in vitro. An anti-prolactin serum also increased ir-SP release and content. In order to determine whether intrapituitary SP participates in TRH-induced prolactin release, anterior pituitaries were incubated with TRH (10(-7) M) and either WIN 62,577, a specific antagonist of the NK1 receptor, or a specific anti-SP serum. Both WIN 62,577 (10(-8) and 10(-7) M) and the anti-SP serum (1:250) blocked TRH-induced prolactin release. In order to study the interaction between TRH and SP on prolactin release, anterior pituitaries were incubated with either TRH (10(-7) M) or SP, or with both peptides. SP (10(-7) and 10(-6) M) by itself stimulated prolactin release. While 10(-7) M SP did not modify the TRH effect, 10(-6) M SP reduced TRH-stimulated prolactin release. SP (10(-5) M) alone failed to stimulate prolactin release and markedly decreased TRH-induced prolactin release. The present study shows that TRH stimulates ir-SP release and increases ir-SP content in the anterior pituitary. Our data also suggest that SP may act as a modulator of TRH effect on prolactin secretion by a paracrine mechanism.
Asunto(s)
Comunicación Paracrina , Adenohipófisis/metabolismo , Prolactina/metabolismo , Sustancia P/farmacología , Hormona Liberadora de Tirotropina/farmacología , Análisis de Varianza , Androstenos/farmacología , Animales , Bencimidazoles/farmacología , Relación Dosis-Respuesta a Droga , Sinergismo Farmacológico , Sueros Inmunes/farmacología , Antagonistas del Receptor de Neuroquinina-1 , Técnicas de Cultivo de Órganos , Adenohipófisis/química , Adenohipófisis/efectos de los fármacos , Prolactina/análisis , Ratas , Ratas Wistar , Estimulación Química , Sustancia P/análisis , Sustancia P/metabolismo , Hormona Liberadora de Tirotropina/metabolismo , Péptido Intestinal Vasoactivo/farmacologíaRESUMEN
OBJECTIVE: In order to determine the mechanism by which nitric oxide (NO) inhibits prolactin release, we investigated the participation of cGMP-dependent cAMP-phosphodiesterases (PDEs) and protein kinase G (PKG) in this effect of NO. METHODS: Anterior pituitary glands of male rats were incubated with inhibitors of PDE and PKG with or without sodium nitroprusside (NP). Prolactin release, and cAMP and cGMP concentrations were determined by RIA. RESULTS AND CONCLUSIONS: The inhibitory effect of NP (0.5 mmol/l) on prolactin release and cAMP concentration was blocked by EHNA (10(-4)mol/l) and HL-725 (10(-4)mol/l), inhibitors of cGMP-stimulated cAMP-PDE (PDE2). 8-Br-cGMP (10(-4) and 10(-3)mol/l), which mimics cGMP as a mediator of NP effects on prolactin release, also decreased cAMP concentration. Zaprinast (10(-4)mol/l), a selective inhibitor of specific cGMP-PDE (PDE5), potentiated the NP effect on cAMP concentration. Rp-8-[(4-chlorophenyl)thio]-cGMP triethylamine (Rp-8-cGMP, 10(-7)-10(-6)mol/l), an inhibitor of PKG, reversed the effect of NP on prolactin release. The present study suggests that several mechanisms are involved in the inhibitory effect of NO on prolactin release. The activation of PDE2 by cGMP may mediate the inhibitory effect of NO on cAMP concentration and therefore on prolactin release. NO-activated PKG may also be participating in the inhibitory effect of NO on prolactin release.
Asunto(s)
Óxido Nítrico/farmacología , Hidrolasas Diéster Fosfóricas/metabolismo , Adenohipófisis/efectos de los fármacos , Adenohipófisis/metabolismo , Prolactina/metabolismo , Proteínas Quinasas/metabolismo , 3',5'-AMP Cíclico Fosfodiesterasas/metabolismo , 3',5'-GMP Cíclico Fosfodiesterasas/antagonistas & inhibidores , 3',5'-GMP Cíclico Fosfodiesterasas/metabolismo , Animales , AMP Cíclico/metabolismo , GMP Cíclico/análogos & derivados , GMP Cíclico/metabolismo , GMP Cíclico/farmacología , Proteínas Quinasas Dependientes de GMP Cíclico , Sinergismo Farmacológico , Activación Enzimática/efectos de los fármacos , Inhibidores Enzimáticos/farmacología , Masculino , Nitroprusiato/farmacología , Inhibidores de Fosfodiesterasa/farmacología , Purinonas/farmacología , Ratas , Ratas WistarRESUMEN
The release of cytokines during infection, inflammation and stress induces brain-mediated responses, including alterations of neuroendocrine functions. We examined the effect of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) on release of gamma-aminobutyric acid (GABA) from mediobasal hypothalamic (MBH) explants and posterior pituitaries (PP) of male rats. IL-6 (10 ng/ml) did not modify basal GABA release from MBH and PP, but significantly increased GABA release under depolarizing conditions (40 mM K(+)). This effect was abolished by incubation of the tissue with indomethacin, an inhibitor of cyclooxygenase activity, indicating that prostaglandins could mediate the stimulation of GABA release induced by IL-6. On the contrary, TNF-alpha (50 ng/ml) significantly decreased K(+)-evoked GABA release from both MBH and PP. This inhibitory effect was not modified by indomethacin. Neither IL-6 nor TNF-alpha affected nitric oxide synthesis, as measured by [(14)C]citrulline production. The current results indicate that IL-6 stimulates GABA release from both hypothalamus and posterior pituitary by a mechanism mediated by prostaglandins. On the contrary, TNF-alpha inhibits GABA release from both tissues. These results suggest the possibility that GABAergic activity in the hypothalamic-pituitary axis could be involved in neuroendocrine responses to cytokines.
Asunto(s)
Hipotálamo Medio/metabolismo , Interleucina-6/farmacología , Neurohipófisis/metabolismo , Factor de Necrosis Tumoral alfa/farmacología , Ácido gamma-Aminobutírico/metabolismo , Animales , Inhibidores de la Ciclooxigenasa/farmacología , Hipotálamo Medio/efectos de los fármacos , Hipotálamo Medio/enzimología , Técnicas In Vitro , Indometacina/farmacología , Interleucina-6/antagonistas & inhibidores , Masculino , Potenciales de la Membrana/efectos de los fármacos , Óxido Nítrico/metabolismo , Óxido Nítrico Sintasa/metabolismo , Neurohipófisis/efectos de los fármacos , Neurohipófisis/enzimología , Potasio/agonistas , Potasio/antagonistas & inhibidores , Potasio/farmacología , Ratas , Ratas WistarRESUMEN
We studied the internalization and intracellular distribution of [3H] GABA in rat anterior pituitary cells. Electron microscopic autoradiography of anterior pituitary fragments or dispersed pituitary cells incubated with [3H] GABA showed that lactotrophs and, to a lesser extent, somatotrophs were the only cells that contained radioactive grains. Grain density analysis performed on dispersed pituitary cells after a pulse-chase experiment (10 min pulse and then change to a medium without radioactive GABA for various periods up to 2 h) revealed that GABA internalized by lactotrophs was distributed in various intracellular membranous organelles. Of the cell compartments examined, plasma membrane, Golgi apparatus, mitochondria and secretory granules had different time-dependent labeling patterns. The highest grain density values were associated with plasma membrane (at the first chase time) and the Golgi apparatus. Mitochondria and secretory granules also showed significant grain density values. A similar pattern of distribution was observed when fragments of prolactin-secreting pituitary adenomas were incubated with [3H] GABA. These results provide morphological data on the cellular specificity and intracellular distribution of GABA in anterior pituitary cells.
Asunto(s)
Microscopía Electrónica , Adenohipófisis/metabolismo , Adenohipófisis/ultraestructura , Ácido gamma-Aminobutírico/metabolismo , Animales , Autorradiografía , Compartimento Celular/efectos de los fármacos , Compartimento Celular/fisiología , Hormona del Crecimiento/metabolismo , Humanos , Masculino , Prolactina/metabolismo , Prolactinoma/metabolismo , Prolactinoma/patología , Prolactinoma/ultraestructura , Ratas , Ratas Wistar , Tritio , Ácido gamma-Aminobutírico/farmacologíaRESUMEN
The effect of glutamate (GLUT) and its ionotropic receptor agonists on K(+)-evoked GABA release from the neurointermediate lobe (NIL) was investigated in diestrus, ovariectomized, ovariectomized-estrogenized female rats and intact male rats. GLUT and N-methyl-D-aspartate (NMDA) increased K(+)-evoked GABA release from the NIL in all the experimental groups. This stimulatory effect of NMDA was blocked by specific NMDA receptor antagonists but not by non-NMDA receptor antagonists. However, kainate did not modify evoked GABA release from the NIL in any of these groups. Neither GLUT nor NMDA modified nitric oxide synthase activity. These results indicate that GLUT, acting through NMDA receptors, stimulates evoked GABA release from the NIL of female and male rats. This effect is not influenced by gonadal status and does not appear to be mediated by nitric oxide production.
Asunto(s)
Estradiol/farmacología , Ácido Glutámico/farmacología , N-Metilaspartato/farmacología , Neurohipófisis/fisiología , Receptores de N-Metil-D-Aspartato/fisiología , Ácido gamma-Aminobutírico/metabolismo , 2-Amino-5-fosfonovalerato/farmacología , Animales , Maleato de Dizocilpina/farmacología , Antagonistas de Aminoácidos Excitadores/farmacología , Femenino , Masculino , Ovariectomía , Neurohipófisis/efectos de los fármacos , Potasio/farmacología , Quinoxalinas/farmacología , Ratas , Ratas WistarRESUMEN
We have previously reported that neurokinin A (NKA), a tachykinin closely related to substance P, increases the release of prolactin (PRL) from the anterior pituitary gland of male rats, but not from pituitaries of ovariectomized (OVX) female rats. In this study, we evaluated the influence of estrogens in the action of NKA on PRL secretion in female rats. NKA stimulated the in vitro release of PRL from pituitary glands of OVX-chronically estrogenized rats, and of proestrus and estrus rats, but had no effect in anterior pituitaries of diestrus rats. In addition, we observed that cultured anterior pituitary cells of OVX rats responded to NKA only when they were incubated for 3 days in the presence of estradiol 10(-9) M. This effect was blocked by L-659,877, an NK-2 receptor antagonist. We also studied the action of NKA on PRL release during lactation. The response of anterior pituitary cells to NKA was variable over this period. The maximal sensitivity to NKA was observed at day 10 of lactation. Furthermore, the blockade of endogenous NKA by the administration of an anti-NKA serum to lactating rats reduced the PRL surge induced by the suckling stimulus. These results show that the responsiveness of the anterior pituitary gland of female rats to NKA is modulated by the endocrine environment, and suggest that NKA may participate in the control of PRL secretion during the estrus cycle and lactation.
Asunto(s)
Estradiol/farmacología , Neuroquinina A/farmacología , Adenohipófisis/metabolismo , Prolactina/metabolismo , Animales , Técnicas de Cultivo de Célula , Células Cultivadas , Estro/metabolismo , Femenino , Lactancia/metabolismo , Técnicas de Cultivo de Órganos , Ovariectomía , Péptidos Cíclicos/farmacología , Adenohipófisis/efectos de los fármacos , Ratas , Receptores de Neuroquinina-2/antagonistas & inhibidoresRESUMEN
TNF-alpha plays a critical role in the cascade of neuroendocrine events during inflammation and septic shock. It also affects the release of pituitary hormones and acts as a growth factor in immune and nonimmune cells. The aim of the present study was to investigate the release of TNF-alpha from rat anterior pituitary cells and the effect of the steroid medium on its release. Cultured anterior pituitary cells from lactating rats spontaneously released TNF-alpha. The presence of lipopolysaccharide (LPS, 0.1 microg/mL) in the culture medium significantly increased TNF-alpha release and inhibited prolactin release. Chronic estrogenization of ovariectomized rats or the presence of 17 beta-estradiol in the culture medium also increased TNF-alpha release. LPS significantly stimulated TNF-alpha release in all groups and abrogated the estrogen-induced prolactin release. We also investigated the effect of TNF-alpha on prolactin release. The presence of TNF-alpha (50 ng/mL) in the culture medium inhibited prolactin release from anterior pituitary cells. These data show that anterior pituitary cells in culture release TNF-alpha and that this release is stimulated by estrogens. Our results also indicate that LPS inhibits prolactin release in an estrogenic environment, suggesting that TNF-alpha could affect pituitary hormone release during endotoxemia.
Asunto(s)
Lipopolisacáridos/farmacología , Adenohipófisis/metabolismo , Prolactina/metabolismo , Factor de Necrosis Tumoral alfa/metabolismo , Animales , Células Cultivadas , Estradiol/farmacología , Femenino , Lactancia , Ovariectomía , Adenohipófisis/efectos de los fármacos , Ratas , Ratas WistarRESUMEN
The purpose of the present study was to examine the in vitro effect of L-glutamate and its agonists on basal and potassium-evoked GABA release from incubated mediobasal hypothalamus (MBH) of intact, ovariectomized (OVX) and OVX-estrogenized female rats. L-glutamate (100 microM) decreased evoked GABA release from MBH of intact female rats in diestrus. NMDA and quisqualate (10 and 100 microM) modified neither basal nor evoked hypothalamic GABA release of intact rats. However, kainate (10 and 100 microM) decreased hypothalamic basal and evoked GABA release of intact rats. Kainate induced no changes in basal or in evoked GABA release from hypothalami of OVX rats, but decreased GABA release in chronically estrogenized rats. DNQX (6,7-dinitroquinoxaline-2,3-dione), a non-NMDA receptor antagonist, failed to affect GABA release but blocked the inhibitory effect of kainate. The kainate effect was not Mg2+-sensitive and was not inhibited by D-AP5 (D(-)-2-amino-5-phosphonopentanoic acid), an NMDA-specific receptor antagonist. Kainate induced no changes in nitric oxide synthase activity in MBH of either intact or estrogenized rats. These data indicate that kainate decreases GABA release from MBH of female rats through a non-NMDA receptor subtype, and provide evidence to support the view that kainate-mediated decrease of the hypothalamic GABAergic tone is affected by estrogens.
Asunto(s)
Aminoácidos Excitadores/farmacología , Ácido Glutámico/farmacología , Hipotálamo/efectos de los fármacos , Ácido gamma-Aminobutírico/metabolismo , Animales , Depresión Química , Diestro , Implantes de Medicamentos , Estradiol/administración & dosificación , Estradiol/farmacología , Agonistas de Aminoácidos Excitadores/farmacología , Antagonistas de Aminoácidos Excitadores/farmacología , Femenino , Hipotálamo/metabolismo , Interneuronas/citología , Interneuronas/efectos de los fármacos , Ácido Kaínico/farmacología , N-Metilaspartato/farmacología , Proteínas del Tejido Nervioso/metabolismo , Óxido Nítrico Sintasa/metabolismo , Ovariectomía , Quinoxalinas/farmacología , Ácido Quiscuálico/farmacología , Ratas , Ratas Wistar , Receptores de Glutamato/efectos de los fármacos , Receptores de Glutamato/fisiología , Receptores de N-Metil-D-Aspartato/efectos de los fármacos , Receptores de N-Metil-D-Aspartato/fisiologíaRESUMEN
The effect of nitric oxide donors on intracellular calcium concentration [Ca2+]i was studied in anterior pituitary cells using ratiometric FURA 2 fluorescence measurements. Sodium nitroprusside (NP) induced a transient decrease in [Ca2+]i, after which [Ca2+]i returned to, or even increased over basal values. S-Nitroso glutathione (GSNO) induced a similar decrease. NP also inhibited high [Ca2+]i achieved by depolarization with 25 mM K+. The inhibitory effect of NP was partially blunted by pretreatment with methoxy-verapamil, and in calcium free buffer, and was not altered by thapsigargin. Interestingly, in calcium free buffer there was a significant stimulatory effect of NP, which was partially blunted by thapsigargin. We conclude that NO donors modify [Ca2+]i in anterior pituitary cells. The action is biphasic, with an initial decrease in [Ca2+]i probably related to a decrease of Ca2+ influx through VDCC, and an increase evidenced in calcium free buffer in which the inhibitory component is absent, and partially depends on thapsigargin sensitive calcium stores.
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Calcio/metabolismo , Donantes de Óxido Nítrico/farmacología , Adenohipófisis/metabolismo , Animales , Tampones (Química) , Calcio/administración & dosificación , Bloqueadores de los Canales de Calcio/farmacología , Galopamilo/farmacología , Glutatión/análogos & derivados , Glutatión/farmacología , Líquido Intracelular/metabolismo , Cinética , Masculino , Nitroprusiato/farmacología , Compuestos Nitrosos/farmacología , Potasio/farmacología , Ratas , Ratas Wistar , S-Nitrosoglutatión , Tapsigargina/farmacologíaRESUMEN
The role of vasoactive intestinal peptide (VIP) in the regulation of dopamine (DA) concentration in mediobasal hypothalamus (MBH), posterior and anterior pituitary of ovariectomized (OVX) estrogenized rats was studied using passive immunization against VIP with a specific antiserum (a-VIP). Chronic estradiol administration decreased DA concentration in MBH, and in posterior and anterior pituitary, compared to OVX control rats. DA tissue concentration increased following a-VIP administration to control and estrogenized OVX rats. In vitro study of VIP and a-VIP on DA release from MBH in chronically estrogenized OVX rats showed that estrogens decreased DA evoked-release from MBH;a-VIP increased DA evoked-release from MBH of control OVX and estrogenized rats. VIP decreased DA evoked-release from MBH of OVX rats, but had no effect on estrogenized rats. VIP decreased DA tissue concentration in MBH of OVX control but not of estrogenized rats. It is suggested that VIP decreases DA synthesis and release from hypothalamic neurons in female rats, and that VIP partially mediates the inhibitory effect of long-term estrogen administration on DA release from MBH.
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Dopamina/metabolismo , Estrógenos/fisiología , Sistema Hipotálamo-Hipofisario/metabolismo , Ovariectomía , Péptido Intestinal Vasoactivo/fisiología , Animales , Femenino , Hipotálamo Medio/metabolismo , Inmunización Pasiva , Adenohipófisis/metabolismo , Neurohipófisis/metabolismo , Ratas , Ratas Wistar , Péptido Intestinal Vasoactivo/inmunologíaRESUMEN
The anterior pituitary gland is a site of nitric oxide (NO) production and action, suggesting a local regulatory function. We recently reported that NO inhibits in vitro prolactin release. The aim of the present study was to establish the mechanism of action of NO on prolactin release and to determine whether NO is involved in the inhibitory effect of GABA on prolactin release. Since NO exerts its action through cGMP by activating guanylate cyclase in different tissues, we examined the effect of sodium nitroprusside (NP), a NO releaser, on intrapituitary cGMP levels. Incubation of anterior pituitary glands with 0.5 mM NP 4-fold increased intrapituitary cGMP content, but decreased intrapituitary cAMP levels. In addition, we studied the effect of NP on prolactin release in the presence of LY 83583, an inhibitor of guanylate cyclase activity and 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of phosphodiesterase activity. 10 microM LY 83583 and 0.5 mM IBMX blocked the inhibitory effect of NP on prolactin release. (10(-3) M) 8Br-cGMP, an analogue of cGMP, mimicked the effect of NP on prolactin release. On the other hand, NO seems to be involved in the inhibitory effect of GABA on prolactin release since hemoglobin, a scavenger of NO, and Nw-nitro-L-arginine methyl ester, an inhibitor of NO synthase (NOS), blocked the pituitary response to GABA. Moreover, GABA (10(-6) M) stimulated NOS activity by almost 50%. GABA increased intrapituitary cGMP levels and decreased cAMP. Dopamine stimulated NOS activity weakly. These observations suggest that NO, acting through the guanylate cyclase-cGMP pathway, inhibits prolactin secretion. In addition, NO may be involved in the inhibitory effect of GABA and dopamine on prolactin release.
Asunto(s)
GMP Cíclico/metabolismo , Dopamina/farmacología , Óxido Nítrico/metabolismo , Prolactina/metabolismo , Ácido gamma-Aminobutírico/farmacología , 1-Metil-3-Isobutilxantina/farmacología , Aminoquinolinas/farmacología , Animales , AMP Cíclico/metabolismo , GMP Cíclico/análogos & derivados , GMP Cíclico/farmacología , Inhibidores Enzimáticos/farmacología , Hemoglobinas/farmacología , Masculino , NG-Nitroarginina Metil Éster/farmacología , Neurotransmisores/metabolismo , Inhibidores de Fosfodiesterasa/farmacología , Hipófisis/efectos de los fármacos , Hipófisis/metabolismo , Prolactina/efectos de los fármacos , Ratas , Ratas WistarRESUMEN
We have studied the in vitro effects of neurokinin A (NKA) on anterior pituitary GABA concentration and GABA release from the mediobasal hypothalamus and the neurointermediate lobe of male and ovariectomized female (OVX) rats. NKA significantly decreased the anterior pituitary GABA concentration, while the presence of a specific anti-NKA serum in the incubation medium increased the GABA concentration in this gland. By contrast, NKA did not modify basal or K(+)-evoked GABA release from the mediobasal hypothalamus of male or OVX rats. However, NKA decreased basal and K(+)-evoked GABA release from the neurointermediate lobe. Since GABA inhibits both prolactin (PRL) secretion from the anterior pituitary and the release of several putative PRL-releasing factors from the neurointermediate lobe, the decrease in anterior pituitary GABA concentration and the reduction in tubero-hypophyseal GABAergic activity induced by NKA may contribute to the stimulatory effect of this peptide on PRL secretion.
Asunto(s)
Sistema Hipotálamo-Hipofisario/efectos de los fármacos , Hipotálamo Medio/fisiología , Neuroquinina A/farmacología , Adenohipófisis/fisiología , Ácido gamma-Aminobutírico/metabolismo , Animales , Femenino , Hipotálamo Medio/efectos de los fármacos , Sueros Inmunes , Técnicas In Vitro , Cinética , Masculino , Neuroquinina A/inmunología , Ovariectomía , Adenohipófisis/efectos de los fármacos , Potasio/farmacología , Ratas , Ratas WistarRESUMEN
Previous research indicates that norepinephrine and dopamine stimulate release of luteinizing hormone (LH)-releasing hormone (LHRH), which then reaches the adenohypophysis via the hypophyseal portal vessels to release LH. Norepinephrine exerts its effect via alpha 1-adrenergic receptors, which stimulate the release of nitric oxide (NO) from nitricoxidergic (NOergic) neurons in the medial basal hypothalamus (MBH). The NO activates guanylate cyclase and cyclooxygenase, thereby inducing release of LHRH into the hypophyseal portal vessels. We tested the hypothesis that these two catecholamines modulate NO release by local feedback. MBH explants were incubated in the presence of sodium nitroprusside (NP), a releaser of NO, and the effect on release of catecholamines was determined. NP inhibited release of norepinephrine. Basal release was increased by incubation of the tissue with the NO scavenger hemoglobin (20 micrograms/ml). Hemoglobin also blocked the inhibitory effect of NP. In the presence of high-potassium (40 mM) medium to depolarize cell membranes, norepinephrine release was increased by a factor of 3, and this was significantly inhibited by NP. Hemoglobin again produced a further increase in norepinephrine release and also blocked the action of NP. When constitutive NO synthase was inhibited by the competitive inhibitor NG-monomethyl-L-arginine (NMMA) at 300 microM, basal release of norepinephrine was increased, as was potassium-evoked release, and this was associated in the latter instance with a decrease in tissue concentration, presumably because synthesis did not keep up with the increased release in the presence of NMMA. The results were very similar with dopamine, except that reduction of potassium-evoked dopamine release by NP was not significant. However, the increase following incubation with hemoglobin was significant, and hemoglobin, when incubated with NP, caused a significant elevation in dopamine release above that with NP alone. In this case, NP increased tissue concentration of dopamine along with inhibiting release, suggesting that synthesis continued, thereby raising the tissue concentration in the face of diminished release. When the tissue was incubated with NP plus hemoglobin, which caused an increase in release above that obtained with NP alone, the tissue concentration decreased significantly compared with that in the absence of hemoglobin, indicating that, with increased release, release exceeded synthesis, causing a fall in tissue concentration. When NO synthase was blocked by NMMA, the release of dopamine, under either basal or potassium-evoked conditions, was increased. Again, in the latter instance the tissue concentration declined significantly, presumably because synthesis did not match release. Therefore, the results were very similar with both catecholamines and indicate that NO acts to suppress release of both amines. Since both catecholamines activate the release of LHRH, the inhibition of their release by NO serves as an ultra-short-loop negative feedback by which NO inhibits the release of the catecholamines, thereby reducing the activation of the NOergic neurons and decreasing the release of LHRH. This may be an important means for terminating the pulses of release of LHRH, which generate the pulsatile release of LH that stimulates gonadal function in both male and female mammals.