COMPARISON OF THE ABILITY OF THE THREE ENDOGENOUS GNRHS TO STIMULATE RELEASE OF FOLLICLE-STIMULATING HORMONE AND LUTEINIZING HORMONE IN CHICKENS

Authors: Proudman, John; SCANES, COLIN - IOWA STATE UNIVERSITY; JOHANNSEN, SARA - IOWA STATE UNIVERSITY; BERGHMAN, LUC - TEXAS A&M UNIVERSITY; Camp, Mary

Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2005
Publication Date: 8/8/2006
Citation: Proudman, J.A., Scanes, C.G., Johannsen, S.A., Berghman, L.R., Camp, M.J. 2006. Comparison of the ability of the three endogenous gnrhs to stimulate release of follicle-stimulating hormone and luteinizing hormone in chickens. Domestic Animal Endocrinology.

Interpretive Summary: The secretion of two important reproductive hormones, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), is controlled, in mammals, by a brain hormone known as gonadotropin releasing hormone (GnRH). In birds, there are three different GnRHs. One, cGnRH-I, is thought to be the physiological releasing hormone for LH. There is controversy as to whether any of the GnRHs cause the secretion of FSH in the bird. In the chicken, unlike mammals, FSH and LH are produced in separate cells and pulses of these hormones are largely secreted independently, suggesting that each may be controlled independently. In these experiments, we compared the abilities of three GnRHs to release LH and FSH in immature pullets and in mature roosters. We found that all three releasing factors will stimulate secretion of LH to varying degrees. Lamprey GnRH-III, which has been shown to selectively cause FSH release in some mammals, did not stimulate FSH secretion in roosters. Only chicken GnRH-II produced a significant increase in FSH secretion in roosters, and this increase was modest compared to its effect on LH. None of the releasing factors stimulated FSH secretion in 17-wk old females. We conclude that none of the releasing factors known to exist in the bird is either a specific or a potent stimulus for FSH secretion in the chicken, and that the mechanism by which independent FSH secretion occurs in the chicken remains unknown. This information will help scientists to better understand the factors controlling reproduction in poultry.

Technical Abstract: It is well established that GnRH can stimulate the release of LH and FSH in mammals. Two GnRHs have been found in the chicken hypothalamus, cGnRH-I and cGnRH-II. There is controversy as to whether either peptide can stimulate release of FSH in birds. The present studies compared the ability of cGnRH-I and -II to stimulate the release of FSH and LH in chickens. Lamprey (l) GnRH-III may be a specific releasing factor for FSH, as it selectively stimulates FSH release in rodents and cattle, and has been detected in the hypothalamus of rodents, sparrows, and chickens. Therefore, the ability of lGnRH-III to stimulate LH and FSH release was also examined. In our first experiment, the effects of cGnRH-I and -II were studied using 17-wk prepubertal females. Intravenous injection of cGnRH-II at 1 and 10 ug/kg b.w. significantly increased LH secretion more than did cGnRH-I. Neither peptide significantly increased plasma FSH levels. In our second study, we administered cGnRH-I, cGnRH-II or lGnRH-III to mature males maintained on a short photoperiod. cGnRH-II was again more potent than cGnRH-I in stimulating LH release, while lGnRH-III produced a modest LH rise. No GnRH peptide provided specific or potent stimulus to FSH secretion, although the high dose of cGnRH II modestly enhanced FSH levels in the adult male (P<0.05). Our results are not consistent with the view that lGnRH-III is a specific FSH-releasing hormone across multiple classes of vertebrates. We conclude that the mechanism by which independent release of FSH occurs in chickens remains unresolved.