A Homolog of Mammalian PRL-Releasing Peptide (Fish Arginyl-Phenylalanyl-Amide Peptide) Is a Major Hypothalamic Peptide of PRL Release in Teleost Fish

Abstract

Two PRL-releasing peptides (PrRP20 and PrRP31) were recently identified from mammalian hypothalamus by an orphan receptor strategy, and a C-terminal RF (arginyl-phenylalamyl-) amide peptide (RFa), structurally related to mammalian PrRP, was also identified from the brain of the Japanese crucian carp (C-RFa) by an intestine-contracting assay. However, to date there have been no reported studies that have examined the PRL-releasing effects of RFa in fish. In the present study we determined the cDNA, primary structure, and function of a homolog of the mammalian PrRP20 in the chum salmon, Oncorhynchus keta. An RFa cDNA encoding a preprohormone of 155 amino acids was cloned from the hypothalamus of chum salmon by 3'- and 5'-rapid amplification of cDNA ends. A native RFa was purified from an acid extract of salmon hypothalami by a Sep-Pak C(18) cartridge, affinity chromatography using anti-synthetic C-RFa, and reverse phase HPLC on an ODS-120T column. The salmon RFa proved to be identical with C-RFa on the basis of elution position on reverse phase HPLC. Immunocytochemical staining in rainbow trout, Oncorhynchus mykiss, revealed that C-RFa-immunoreactive cell bodies were located in the posterior part of hypothalamus and C-RFa-immunoreactive fibers were abundant from the hypothalamus to the ventral telencephalon. A small number of immunoreactive fibers were projected to the pituitary and terminated close to the PRL cells in the rostral pars distalis and to the somatolactin (SL) cells in the pars intermedia. The hypophysiotropic effects of the fish homolog were determined on the release of PRL, SL, and GH from the pituitary of the rainbow trout. Plasma PRL and SL levels were increased at 3 and 9 h, respectively, after ip injection of the synthetic C-RFa into the rainbow trout at doses of 50 and 500 ng/g body weight. In contrast, plasma GH levels were decreased after 1 h at 500 ng/g body weight. Perifusion of the trout pituitaries with synthetic C-RFa at concentrations of 10 pM to 100 nM demonstrated maximum PRL release at 100 pM and maximum SL release at 10 and 100 nM. However, GH release was not affected. These data are the first to demonstrate that a homolog of mammalian PrRP (fish RFa) is a major hypothalamic peptide of PRL release in teleost fish.

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.…”

Expression of prolactin-releasing peptide and prolactin in the euryhaline mudskippers (Periophthalmus modestus): prolactin-releasing peptide as a primary regulator of prolactin

“…Immunocytochemical staining of PrRP was carried out with anti-synthetic C-RFa serum using a Histofine immunostaining kit (Nichirei, Tokyo, Japan) basically as described by Moriyama et al (2002). Anti-synthetic C-RFa serum was diluted 1:5000 with 0·1 M phosphate buffer (pH 7·4) containing 0·75% NaCl and 0·3% Triton X-100.…”

Structurally conserved C-RFa revealed prolactin releasing activity in vitro and gene expression changes in pituitary of seasonally acclimatized carp

“…The deduced preprohormone precursor present 95% and 89% similarity to crucian carp and zebrafi sh respectively, while the mature peptide presented 100% identity to all fi sh bioactive C _ RFa (Kwong and Woo 2008;Montefusco-Siegmund et al 2006;Moriyama et al 2002;Seale et al 2002). The conservation over 400 MYA in sequence and structure of teleost C-RFa to mammalian PrRP (60%) strongly suggests a pivotal role for this hypothalamic peptide in vertebrates.…”

“…A similar C-RFa peptide was identifi ed in chum salmon (Oncorhynchus keta), Atlantic salmon (salmo salar), tilapia (Oreochromis mossambicus) and silver sea bream (Sparus sarba) (Kwong and Woo 2008;Montefusco-Siegmund et al 2006;Moriyama et al 2002;Seale et al 2002). The cDNA encoding the preprohormones encodes a putative bioactive peptide of 20 amino acids, identical in all the teleost species studied and 65% similar to homologous human PrRP20 (h-PrRP).…”