Pituitary and testicular functions in sexually mature rhesus monkeys under high-dose LRH-agonist treatment.

Treatment with high doses of LRH-agonists leads to a down-regulation of testicular LH/hCG receptors and is accompanied by a suppression of spermatogenesis in some laboratory animals. In order to test whether this may provide an approach to male fertility control, 4 adult rhesus monkeys were treated with very high doses of LRH-agonist, D-Ser(TBu)6-LHR-ethylamide (100 micrograms daily) for 10 weeks during the breeding season. There was a decrease in testicular volume after 3 weeks of treatment. Serum LH and testosterone levels were suppressed. Sperm counts were stimulated during the first 6 weeks of treatment. At the end of treatment sperm counts, although lower, were still in the normal range. The chronic treatment schedule resulted in a decrease in pituitary responsiveness to an acute challenge with 4 micrograms agonist iv, indicating a desensitization of the pituitary. However, the testosterone response remained unchanged. This study using extremely high doses of the agonist indicates that, compared to the rat, male primates are far more resistant to the suppressive effects of LRH-agonists.