Contraceptive potentiality of STS-557--a feasibility study in male bonnet monkey (Macaca radiata)

STS-557 (17 alpha-cyanomethyl-17 beta-hydroxy-estra-4, 9(10)-diene-3-one) was administered (i.m.) to two groups (4 in each group) of adult male bonnet monkeys at a daily dose of 10 mg/monkey for 12 weeks (first group) and 5 mg/monkey for 14 weeks (second group). Treatment with the 10 mg dose resulted in a significant decline in the count, motility, acrosin and hyaluronidase activities and the fertilizing ability (zona-free hamster egg penetration assay) of spermatozoa by the 6th week of initiation of treatment. The circulating level of STS-557 was low after one week and increased from the 2nd week of treatment when the serum level of testosterone was significantly reduced. Complete recovery was observed by the 11th week after withdrawal of treatment. The treatment with the 5 mg dose had minor and inconsistent effect on the motility, hyaluronidase and acrosin activity, and the fertilizing ability of spermatozoa in addition to the blood level of testosterone. STS-557 may have the potentiality to be used as a chemical contraceptive in the male but compensation for the reduced level of blood testosterone may be necessary.