PRIMARY STRUCTURE OF SOLITARY FORM OF GONADOTROPIN-RELEASING-HORMONE (GNRH) IN CICHLID PITUITARY - 3 FORMS OF GNRH IN BRAIN OF CICHLID AND PUMPKINSEED FISH

GnRH is a decapeptide family with at least nine distinct structures. V ertebrates, except for most placental mammals, have more than one of t hese GnRH forms within the brain. We report chromatographical and immu nological evidence that three forms of GnRH are in the brains of both cichlid (Haplochromis burtoni) and pumpkinseed (Lepomis gibbosus) fish es. We argue that the three forms correspond to those previously descr ibed as sea bream GnRH (sbGnRH), chicken GnRH-II and salmon GnRH. In c ontrast, only one GnRH form was present in the pituitary of the cichli d and is identified as sbGnRH by amino acid sequence. This is the firs t report in which the primary structure of GnRH is determined from pit uitary tissue. The N-terminus was identified by monitoring the digesti on of the peptide by pyroglutamate aminopeptidase with matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS). The amida tion of the C-terminus was established using an esterification procedu re for monitoring with MALDI-MS. This report supports the idea that th ree forms of GnRH within one species is widespread in the order Percif ormes. The present study establishes sbGnRH as the third GnRH form in H. burtoni and predicts that sbGnRH is synthesized in preoptic neurons , then transported to the pituitary in the preoptic-hypophyseal axons for the release of one or both gonadotropins.