Novel fish hypothalamic neuropeptides stimulate the release of gonadotrophins and growth hormone from the pituitary of sockeye salmon

We recently identified a cDNA encoding three novel fish hypothalamic neuropeptides, having LPXRF-NH2 from the goldfish brain. In this Study, to clarify the physiological functions of these three LPXRFamide peptides (gfLPXRFa-1, -2, and -3), we analysed the localisation and hypophysiotrophic activity of these peptides using sockeye salmon, Oncorhynchus nerka, in which immunoassay systems for several interior pituitary hormones have been developed. gfLPXKFa-immunoreactive cell bodies were detected in the nucleus posterioris periventricularis of the hypothalamus and immunooreactive fibres were distributed in various brain regions and the pituitary. We also detected gfLPXRFa-immunoreactivity in the pituitary by competitive enzyme-linked immunosorbent assay combined with reversed-phase HPLC. These three gfLPXRFamide peptides stimulated the release of FSH, LH and GH, but did not affect the release of prolactin (PRL) and soiatolactin (SL) from cultured pituitary cells ' These results suggest that novel fish hypothalamic LPXR- Famide peptides exist in the brain and pituitary of sockeye salmon and stimulate the release of gonadotrophins and GH from the pituitary.