Identification of the second gonadotropin-releasing hormone in chicken hypothalamus: evidence that gonadotropin secretion is probably controlled by two distinct gonadotropin-releasing hormones in avian species.

TLDR

Avian hypothalamus contains the previously reported [Gln8]LHRH peptide. The peptide was characterized by chymotryptic and thermolytic digestion followed by amino acid and terminal analyses, and its structure was confirmed by comparison with a synthetic decapeptide. A novel peptide, chicken GnRH‑II, was isolated, its full decapeptide sequence determined, and it was shown to be 32 % as potent as mammalian LHRH but eight times more potent than chicken LHRH, suggesting that two distinct GnRHs regulate gonadotropin secretion in birds.

Abstract

A new peptide having gonadotropin-releasing activity distinct from the known luteinizing hormone-releasing hormones ( LHRHs ) has been identified in a chicken hypothalamic extract. The existence of [Gln8]LHRH in avian hypothalamus has been reported previously. The new molecular species of gonadotropin-releasing activity, named chicken gonadotropin-releasing hormone II (chicken GnRH-II), has been isolated recently in a yield of 7 micrograms, starting from 10,000 chicken hypothalami. Structural analyses have been performed on the peptide fragments derived from chymotryptic and thermolytic digests of chicken GnRH-II by amino acid analyses and terminal analyses. The full sequence of chicken GnRH-II has been determined to be: pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2. A synthetic decapeptide with the above sequence was verified to be chromatographically identical to natural chicken GnRH-II. For further structural confirmation, chymotryptic and thermolytic peptides from synthetic and natural chicken GnRH-II also were identified. Thus, the structure of chicken GnRH-II has been definitely established. The gonadotropin-releasing potency of chicken GnRH-II was about 32% of that of mammalian LHRH and 8 times more potent than chicken LHRH, as estimated from the bioassay with rat anterior pituitary cells. Our results indicate that gonadotropin secretion is probably controlled by two distinct GnRHs , at least in avian species.