PLASMA TESTOSTERONE IN BULLS

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Abstract
Injections of 375–6000 IU HCG to 10 bulls, 7 months of age, gave no dose related response in plasma testosterone measured in samples collected during the following 9 h. However, an increase in the dose of HCG was followed by 1) an increase in maximal testosterone values (r = + 0.9), 2) an extension of the period between injection and maximal value, and 3) an increased duration of the response. Single iv or im injections of 6000 IU PMSG to 4 bulls led to initial elevations of plasma testosterone to about the spontaneous diurnal maxima, followed by a prolonged additional elevation to approximately 2 to 3 times this level. Values decreased to pre-treatment levels on days 16–18 following im injection and 20–22 days following iv injection. In dose-response studies 750–12 000 IU PMSG gave similar response in plasma testosterone measured in samples collected 4 and 5 h after the injection, while a dose-dependent response in plasma testosterone was found with regard to maximal values as well as duration of the effect. When comparing the plasma testosterone response following the two gonadotrophins some differences were found. Injections of 6000 IU of the two gonadotrophins showed that PMSG required longer time to cause any effect upon plasma testosterone than HCG. A dose of 375 IU HCG was sufficient to evoke a prolonged effect while 750 IU PMSG was not. However, when a sufficient PMSG dose to evoke a prolonged effect was used, the duration of the effect was markedly longer after PMSG administration than after a similar HCG-dose.