Influence of Coexisting Hypothalamic Messengers on Growth Hormone Secretion from Rat Anterior Pituitary Cells in vitro

Abstract

An increasing number of messengers have recently been found to coexist with growth hormone (GH)-releasing factor (GRF) in hypothalamic neurons. In view of a possible cosecretion of these substances with GRF into the portal circulation, the effect of synthetic rat hypothalamic GRF(1–43) alone, or together with dopamine (DA), L-dopa, γ-aminobutyric acid (GABA), neurotensin (NT) or galanin (GAL) on GH release was investigated by using dispersed rat anterior pituitary cells in monolayer culture. GRF in concentrations of 10^-16–10^-7M stimulated GH release from somatotrophs in a dose-related manner. DA (10^-5 M), L-dopa (10^-8 and 10^-5-M) and GABA (10^-9 and 10^-5M) did not affect basal GH release, whereas DA, but not L-dopa or GABA, significantly suppressed GRF-induced GH secretion. However, the inhibitory effect of DA on GRF-stimulated GH secretion was not observed in the presence of somatostatin (10^-6M).NT (10^-6M) and GAL (10^-6M) did not change basal GH release. GAL, but not NT, inhibited GRF-stimulated GH release, but the addition of NT abolished the inhibitory actions of both GAL and DA. These results indicate that substances, probably coreleased with GRF from the same nerve endings, interact in the regulation of GH secretion at the pituitary level.

Effect of Growth Hormone (GH)-Releasing Peptide (GHRP) on the Release of GH from Cultured Anterior Pituitary Cells in Cattle.

“…Moreover, GH secretion induced by GHRH, GHRP, and PACAP from rat pituitary cells was inhibited by SRIF in vitro [11,23]. Furthermore, the inhibitory effect of SRIF on GHRH-induced GH secretion has been reported in in vitro studies in rats [2,24], in chickens [25], and also in vivo in young bulls [26]. The present study is in agreement with the demonstration that GHRP may be a useful probe to use in investigating the GH secretory mechanisms as reported by Badger et al [20], in their study on rat pituitary cells.…”

“…These two hypothalamic peptides are released from nerve endings in the median eminence and reach the anterior pituitary via the hypophysial-portal circulation [1][2][3]. Moreover, it has been reported that GHRH and SRIF regulate mitotic activities of GH-producing cells and that the effect of GHRH is possibly mediated by cyclic AMP [4].…”

Galanin is an estrogen-inducible, secretory product of the rat anterior pituitary.

“…Several studies have shown that galanin administered to animals increases pituitary secretion of prolactin and GH (6)(7)(8)(9)(10)(11)). Galanin appears to mediate these effects at the hypothalamic level, and recent studies showed no direct effect of galanin on cultured pituitary cells (6,12,13). However, these studies used pGal and, therefore, do not exclude a direct effect of the homologous peptide on rat prolactin-and GH-producing cells.…”

“…Intravenous pGal injection in humans stimulates GH release and augments the GH release induced by exogenous GH-releasing hormone (10, 11). pGal has little stimulatory effect on the release of these hormones in isolated pituitary preparations (6,(12)(13)(14), and there is evidence that its effects are exerted indirectly via the release of dopamine (for prolactin) and somatostatin (for GH) (8,11,15). Intracerebroventricular pGal increases luteinizing hormone release in ovariectomized rats treated with exogenous estrogen and progesterone (16).…”

Paradoxical GH response to TRH during status epilepticus in man

“…Dopamine also inhibits GH secretion from cultured pituitary cells, i.e. at the pituitary level (37,38). In contrast, the systemic administration of dopamine results in GH increment (27), probably due to the activation of hypothalamic hormones stimulating GH release.…”