In-vitro and in-vivo responses to chicken LHRH-I and chicken LHRH-II in male turkeys (Meleagris gallopavo)

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Abstract
Stimulation of male turkey hypophyses in vitro with chicken (c)LHRH-I, cLHRH-II or porcine (p)LHRH (0·1 μmol/l) using a perifusion technique caused an increase in the release of LH. In this system, cLHRH-II was approximately 2·5-fold more potent than cLHRH-I and pLHRH which were equipotent. The difference was due to a greater amplitude of the response but not to a prolonged action. Hypophyseal desensitization to a subsequent stimulation was induced when the interval between stimulations was 30 min, but did not occur when lengthened to 60 or 120 min. Injection of a single dose of cLHRH-I or -II in vivo at doses of 10 and 0·1 nmol/kg body weight stimulated increases in the plasma concentration of LH and testosterone initiated within 1 or 10 min after injection respectively. As in vitro, cLHRH-II induced greater responses, which were dose-related, than did cLHRH-I. However, this difference could be attributed to a greater potency of cLHRH-II and to a more prolonged action. At the 10 nmol/kg dose, the shape of the LH response to cLHRH-II changed; it consisted of an initial increase during 10 min after injection, followed by a more sustained phase during which LH levels were still increasing between 20 and 60 min after injection. In contrast, after an injection of cLHRH-I at doses of 10 or 0·1 nmol/kg or cLHRH-II at a dose of 0·1 nmol/kg, LH levels were at a peak within 5 min and thereafter declined gradually. This decrease in LH may therefore simply be related to the disappearance of the LHRH from the circulation or to other unknown actions of cLHRH-II, when high doses are used. Journal of Endocrinology (1992) 132, 387–393

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