RESUMO
It appears that PACAP has a direct action on somatotrophs to release GH. The intracellular signal transduction mechanisms for PACAP might be similar to but partly distinct from those for GRH. PACAP might play a role in GH secretion induced by serotoninergic mechanisms but not in ultradian rhythm of GH secretion in the rat. PACAP can stimulate PRL release from the pituitary in rats possibly through indirect paracrine effect. In addition, PACAP might participate in regulation of PRL secretion via hypothalamic VIP.
Assuntos
Hormônio do Crescimento/metabolismo , Neuropeptídeos/fisiologia , Adenoma/metabolismo , Animais , Células Cultivadas , Humanos , Hipotálamo/química , Hipotálamo/efeitos dos fármacos , Hipotálamo/fisiologia , Neuropeptídeos/análise , Neuropeptídeos/farmacologia , Polipeptídeo Hipofisário Ativador de Adenilato Ciclase , Hipófise/química , Hipófise/efeitos dos fármacos , Hipófise/fisiologia , Neoplasias Hipofisárias/metabolismo , Prolactina/metabolismo , Receptores de Polipeptídeo Hipofisário Ativador de Adenilato Ciclase , Receptores do Hormônio Hipofisário/análise , Receptores do Hormônio Hipofisário/fisiologiaRESUMO
Immunoreactive galanin and galanin message associated peptide (GMAP) were detectable in rat hypothalamus in the concentration of 563 +/- 23 and 14.3 +/- 3.1 fmol/hypothalamus, respectively. gamma-Aminobutyric acid (GABA) elicited a dose-related increase in galanin release from rat hypothalamic fragments, which was inhibited by picrotoxin, a GABA antagonist. Growth hormone (GH) secretion from rat anterior pituitary cells were stimulated by rat galanin, but not by GMAP. These findings suggest that hypothalamic galanin, but not GMAP, may play roles in GH secretion induced by GABAergic mechanisms in the rat.
Assuntos
Galanina/farmacologia , Hormônio do Crescimento/metabolismo , Hipotálamo/efeitos dos fármacos , Fragmentos de Peptídeos/farmacologia , Ácido gama-Aminobutírico/farmacologia , Análise de Variância , Animais , Antagonistas GABAérgicos/farmacologia , Galanina/metabolismo , Hipotálamo/metabolismo , Masculino , Picrotoxina/farmacologia , Adeno-Hipófise/efeitos dos fármacos , Adeno-Hipófise/metabolismo , Ratos , Ratos Wistar , Estimulação QuímicaRESUMO
Pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) stimulated GH secretion in superfused rat anterior pituitary cell in vitro and in conscious male rats in vivo. PACAP-38-induced GH secretion was inhibited by PACAP-(6-38), an N-terminal-deleted analog, at 100-fold concentrations of PACAP-38 both in vitro and in vivo. In contrast, a GH-releasing hormone antagonist did not affect the action of PACAP-38 to stimulate GH release in vitro. Plasma GH increase induced by i.v. injection of 5-hydroxy-L-tryptophan (1 mg/100 g BW), a precursor of serotonin, was blunted by PACAP-(6-38) (1 nmol/100 g BW, i.v.), whereas spontaneous pulsatile GH secretion in conscious male rats, which is governed by hypothalamic GH-releasing hormone and somatostatin, was not affected by repeated i.v. injection of PACAP-(6-36). These findings suggest that PACAP-(6-38) is a potent antagonist of PACAP-38 to stimulate GH secretion both in vivo and in vitro. Taken together with the facts that PACAP-38 is highly concentrated in the hypothalamus and that is released into the hypophysial portal blood, our present findings suggest that PACAP-38 might play a stimulatory role on GH secretion induced by serotoninergic mechanisms in the rat.