Neuroendocrinology

The membrane progesterone receptors (mPRα, -β, -γ, -δ, -ε) are known to mediate rapid non-genomic progesterone functions in different cell types. However, the functions of these receptors in the pituitary have not been reported to date. Here we show that the expression of mPRα was the highest among the mPRs in the rat anterior pituitary gland. Immunostaining of mPRα was detected in somatotrophs, gonadotrophs and lactotrophs. Interestingly, 63% of mPRα-positive cells within the pituitary were lactotrophs suggesting that mPRα is involved in controlling prolactin (PRL) secretion in the pituitary. To test this hypothesis, rat pituitaries were incubated (1h) with either progesterone (P4) or the mPRα specific agonist Org OD 02-0. PRL secretion was then measured by radioimmunoassay (RIA). Results of this experiment revealed that both P4 and Org OD 02-0 decreased PRL secretion. Moreover, results from the GH3 cell line (CCL-82.1 ) showed that P4 and Org OD 02-0 inhibited PRL release, but the...

In 2000, we discovered a novel hypothalamic neuropeptide that actively inhibits gonadotropin release in quail and termed it gonadotropin-inhibitory hormone (GnIH). GnIH peptides have since been identified in most representative species of gnathostomes. They all share a C-terminal LPXRFamide (X = L or Q) motif. GnIH can inhibit gonadotropin synthesis and release by decreasing the activity of GnRH neurons as well as by directly inhibiting pituitary gonadotropin secretion in birds and mammals. To investigate the evolutionary origin of GnIH and its ancestral function, we identified a GnIH precursor gene encoding GnIHs from the brain of sea lamprey, the most ancient lineage of vertebrates. Lamprey GnIHs possess a C-terminal PQRFamide motif. In vivo administration of one of lamprey GnIHs stimulated the expression of lamprey GnRH in the hypothalamus and GTHβ mRNA in the pituitary. Thus, GnIH may have emerged in agnathans as a stimulatory neuropeptide that later diverged to an inhibitory ne...