title: Hypophysiotropic role of RFamide-related peptide-3 in the inhibition of LH secretion in female rats.
abstract: Gonadotropin-inhibitory hormone (GnIH), a newly discovered hypothalamic RFamide peptide, inhibits reproductive activity by decreasing gonadotropin synthesis and release in birds. The gene of the mammalian RFamide-related peptides (RFRP) is orthologous to the GnIH gene. This Rfrp gene gives rise to the two biologically active peptides RFRP-1 (NPSF) and RFRP-3 (NPVF), and i.c.v. injections of RFRP-3 suppress LH secretion in several mammalian species. In this study, we show whether RFRP-3 affects LH secretion at the pituitary level and/or via the release of GnRH at the hypothalamus in mammals. To investigate the suppressive effects of RFRP-3 on the mean level of LH secretion and the frequency of pulsatile LH secretion in vivo, ovariectomized (OVX) mature rats were administered RFRP-3 using either i.c.v. or i.v. injections. Furthermore, the effect of RFRP-3 on LH secretion was also investigated using cultured female rat pituitary cells. With i.v. administrations, RFRP-3 significantly reduced plasma LH concentrations when compared with the physiological saline group. However, after i.c.v. RFRP-3 injections, neither the mean level of LH concentrations nor the frequency of the pulsatile LH secretion was affected. When using cultured pituitary cells, in the absence of GnRH, the suppressive effect of RFRP-3 on LH secretion was not clear, but when GnRH was present, RFRP-3 significantly suppressed LH secretion. These results suggest that RFRP-3 does not affect LH secretion via the release of GnRH, and that RFRP-3 directly acts upon the pituitary to suppress GnRH-stimulated LH secretion in female rats.
authors.affiliation: Department of Obstetrics and Gynecology, The University of Tokushima Graduate School, Institute of Health Biosciences, Tokushima 770-8503, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Murakami
authors.forename: Toshiya
authors.initials: T
authors.lastname: Matsuzaki
authors.forename: Takeshi
authors.initials: T
authors.lastname: Iwasa
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Yasui
authors.forename: Minoru
authors.initials: M
authors.lastname: Irahara
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Osugi
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Tsutsui
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004435:Eating / Q000187:drug effects; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood* / Q000378:metabolism*; D008297:Male; D009479:Neuropeptides / Q000008:administration & dosage / Q000494:pharmacology*; D010052:Ovariectomy; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D009479:Neuropeptides; C416987:RFamide peptide; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone