EFFECT OF SYNTHETIC LUTEINIZING HORMONE RELEASING HORMONE ON PLASMA LUTEINIZING HORMONE IN THE FEMALE DOMESTIC FOWL, GALLUS DOMESTICUS

SUMMARY A dose of 20 μg luteinizing hormone releasing hormone (LH-RH) was injected i.v. into laying hens at different times in relation to ovulation and into immature hens of different ages. In laying hens a small but significant increase in plasma LH was consistently observed similar in height but shorter in duration than the natural pre-ovulatory surge of LH. The response was markedly less than that seen in cockerels injected with LH-RH. The time of injection of LH-RH in relation to ovulation did not affect the response unless it was administered immediately after the pre-ovulatory LH peak, when no release of LH occurred. The release of LH which normally occurs 4–7 h before ovulation was, however, unaffected by a rise in plasma LH stimulated by injection of LH-RH a short time previously. The lack of response to LH-RH in the 3 h before ovulation may be due to a depletion of the pituitary reserve of available LH since the normal pre-ovulatory peak of LH is more prolonged than that induced by LH-RH. In no case was premature ovulation seen after i.v. administration of LH-RH. After LH-RH injection a striking increase in plasma LH, similar in magnitude to that in the cockerel, was observed in immature hens aged 11 weeks, but the response decreased with age until at 21 weeks, when basal levels of LH had increased, no response occurred. This would appear to be an important modification of the pituitary response to releasing hormone which coincides with the maturation of the hypothalamic-pituitary-gonadal system at the onset of sexual maturity.