A Novel Amphibian Hypothalamic Neuropeptide: Isolation, Localization, and Biological Activity

Abstract

Neuropeptides similar to the molluscan cardioexcitatory Phe-Met-Arg-Phe-NH2 have been identified in several vertebrates and characterized by the RFa motif at their C terminus (RFa peptides). In this study, we sought to identify an amphibian hypothalamic RFa peptide that may regulate secretion of hormones by the anterior pituitary gland. An acid extract of bullfrog hypothalami was passed through C-18 reversed-phase cartridges, and then the retained material was subjected to HPLC, initially using a C-18 reversed-phase column. RFa immunoreactivity was measured in the eluted fractions by a dot immunoblot assay employing an antiserum raised against RFa. Immunoreactive fractions were subjected to further cation exchange and reversed-phase HPLC purification. The isolated peptide was a novel RFa peptide and shown to have the sequence Ser-Leu-Lys-Pro-Ala-Ala-Asn-Leu-Pro-Leu-Arg-Phe-NH2. The cell bodies and terminals containing this peptide were localized immunohistochemically in the suprachiasmatic nucleus and median eminence, respectively. This RFa peptide stimulated, in a dose-related way, the release of GH from cultured pituitary cells, its threshold concentration ranging between 10(-9) and 10(-8) M. This peptide did not have any appreciable effect on the secretion of PRL and gonadotropins. It was ascertained that the peptide was also effective in elevating the circulating GH level when administered systemically. Thus, the amphibian hypothalamus was revealed to contain a novel functional RFa peptide that stimulates GH release. This peptide was designated frog GH-releasing peptide.

Seasonal effects of GnIH on basal and GnRH-induced goldfish somatotrope functions

“…These results indicate that gGnIH can reduce GH release, at least in part, by direct actions on basal GH secretion and by inhibition of GnRHstimulated GH release at the level of the pituitary cells. These results differ from those observed for amphibians and male rats, where the GnIH homolog (fGRP and RFRP3 respectively) stimulates GH secretion in vivo (Koda et al 2002, Johnson et al 2007. Whether the inhibitory effects of i.p.…”

“…In frogs, a GnIH ortholog (termed frog growth hormone-releasing peptide (fGRP)) stimulates GH release in vitro and in vivo (Koda et al 2002, Ukena et al 2003. Similarly, the rat GnIH ortholog RFRP3 increases the levels of GH in plasma (Johnson et al 2007).…”

Identification of 26RFa, a hypothalamic neuropeptide of the RFamide peptide family with orexigenic activity

“…Dunnett's t test; * , P Ͻ 0.05; ** , P Ͻ 0.01. RFRP-1 stimulate prolactin secretion (9,11,14); in birds, GnIH inhibits luteinizing hormone release (15); in amphibians, R-RFa activates growth hormone secretion (33); and in fish, Carassius RFamide increases prolactin and somatolactin secretion (34). Here, we show that 26RFa provokes a massive increase in cAMP formation by rat pituitary cells whereas NPFF and frog R-RFa have little or no effect.…”

Gonadotropin-inhibitory hormone in Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii): cDNA identification, transcript localization and functional effects in laboratory and field experiments

“…Immunohistochemical analysis was performed using the antiserum against quail GnIH raised in a rabbit as described previously (Tsutsui et al 2000, Koda et al 2002. In brief, anesthetized adult female sparrows were perfused with PBS (pH 7·3) followed by fixative solution (4% paraformaldehyde in PBS).…”