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DIURNAL FLUCTUATIONS OF TESTOSTERONE AND LH IN THE RAM: EFFECT OF HCG AND GONADOTROPHIN-RELEASING HORMONE

Summary.: To examine a possible relationship between the release of LH and increasing testosterone levels, blood samples were collected at 2-hr intervals for 24 hr from six mature rams with indwelling jugular cannulae. Although high levels of LH often preceded increases of testosterone, a consistent time relationship between these two hormones was not observed, nor was a diurnal rhythm established for either hormone. The following day, two rams were each injected intravenously with saline, 500 i.u. HCG, or 100 µg synthetic gonadotrophin-releasing hormone (Gn-RH) respectively. Immediately after the injection, blood was collected every 15 min for approximately 4 hr. After Gn-RH, the plasma LH rose 25- to 50-fold within 12 min and was elevated for more than 3 hr. A twofold rise of plasma testosterone followed this increase of LH and testosterone remained high until the end of the experiment. After HCG treatment, the level of testosterone rose threefold within 30 min and did not decline during the experiment, but there was no effect on the LH level. Saline treatment did not influence levels of LH or testosterone.

It was concluded that daily fluctuations of testosterone and LH may occur independently, and no pattern is common to all rams. Treatment with Gn-RH results in a rise in both the testosterone and LH levels, but only testosterone is affected by HCG.

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