A comparison of the luteinizing hormone-releasing activities of synthetic chicken luteinizing hormone-releasing hormone (LH-RH), synthetic porcine LH-RH, and buserelin, and LH-RH analogue, in the domestic fowl

Abstract

The luteinizing hormone-releasing activities of synthetic chicken luteinizing hormone-releasing hormone (chLH-RH), synthetic porcine LH-RH (pLH-RH), and an analogue of LH-RH (buserelin, d-Ser-(Bu t) 6-des-Gly 10-LH-RH ethylamide) were compared in the domestic fowl. In adult cockerels, intravenous injections of 0.5 or 1 μg chLH-RH/kg released the same amount of LH as the same doses of pLH-RH; subcutaneous injections of 0.5 or 1 μg buserelin/kg were about twice as effective as the same doses of pLH-RH. In laying hens, injections of 1, 10, 20, and 50 μg buserelin induced more sustained releases of LH than the corresponding doses of pLH-RH. Daily injections of 1 or 10 μg buserelin/bird or of 10 μg pLH-RH/bird for 12 days synchronized the timing of most ovipositions showing that the injections of releasing hormone could induce preovulatory surges of LH. In contrast with mammals, daily injections of buserelin in laying hens did not reduce pituitary responsiveness to the analogue. It is concluded that the structural difference between mammalian and chicken LH-RH does not affect their LH-releasing activities in the domestic fowl. Although the LH-releasing activity of buserelin in the hen is greater than that of pLH-RH, the difference in activity is not as great as that observed in most mammals. This view is strengthened by the finding that chronic treatment with buserelin, which exerts an antagonistic effect on ovulation in mammals, does not do so in the domestic hen.