title: Lamprey GnRH-III acts on its putative receptor via nitric oxide to release follicle-stimulating hormone specifically.
abstract: Lamprey gonadotropin-releasing hormone-III (l-GnRH-III), the putative follicle-stimulating hormone (FSH)-releasing factor (FSHRF), exerts a preferential FSH-releasing activity in rats both in vitro and in vivo. To test the hypothesis that l-GnRH-III acts on its own receptors to stimulate gonadotropin release, the functional activity of this peptide at mammalian (m) leutinizing hormone (LH)RH receptors transfected to COS cells was tested. l-GnRH-III activated m-LHRH receptors only at a minimal effective concentration (MEC) of 10(-6) M, whereas m-LHRH was active at a MEC of 10(-9) M, at least 1,000 times less than that required for l-GnRH-III. In 4-day monolayer cultured cells, l-GnRH-III was similarly extremely weak in releasing either LH or FSH, and, in fact, it released LH at a lower concentration (10(-7) M) than that required for FSH release (10(-6) M). In this assay, m-LHRH released both FSH and LH significantly at the lowest concentration tested (10(-10) M). On the other hand, l-GnRH-III had a high potency to selectively release FSH and not LH from hemipituitaries of male rats. The results suggest that the cultured cells were devoid of FSHRF receptors, thereby resulting in a pattern of FSH and LH release caused by the LHRH receptor. On the other hand, the putative FSH-releasing factor receptor accounts for the selective FSH release by l-GnRH-III when tested on hemipituitaries. Removal of calcium from the medium plus the addition of EGTA, a calcium chelator, suppressed the release of gonadotropins induced by either l-GnRH-III or LHRH, indicating that calcium is required for the action of either peptide. Previous results showed that sodium nitroprusside, a releaser of nitric oxide (NO), causes the release of both FSH and LH from hemipituitaries incubated in vitro. In the present experiments, a competitive inhibitor of NO synthase, L-NG-monomethyl-L-arginine (300 micro M) blocked the action of l-GnRH-III or partially purified FSHRF. The results indicate that l-GnRH-III and FSHRF act on putative FSHRF receptors by a calcium-dependent NO pathway.
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone; D006728:Hormones / Q000378:metabolism*; D066298:In Vitro Techniques; D007798:Lampreys; D008297:Male; D051379:Mice; D009569:Nitric Oxide / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D051381:Rats; D017207:Rats, Sprague-Dawley; D011966:Receptors, LHRH / Q000235:genetics / Q000378:metabolism*; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D006728:Hormones; D009842:Oligopeptides; D011966:Receptors, LHRH; C448022:gonadotropin-releasing hormone-III; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D007987:Gonadotropin-Releasing Hormone; D005640:Follicle Stimulating Hormone; D011761:Pyrrolidonecarboxylic Acid