Evaluation of sts 557 17 alpha cyano methyl 17 beta hydroxy estra 4 9 10 dien 3 one as a post coital contraceptive in the baboon papio cynocephalus

Castracane V. D.; Goldzieher J. W.

A postcoital interceptive action of STS-557 [17.alpha.-cyanomethyl-17.beta.-hydroxyestra-4,9(10)-diene-3-one], a synthetic progestin, was reported in the mouse, rat and baboon. The effects in the baboon were reinvestigated with a modification of the original protocol: prolongation of the mating period from 6-48 h. The time of mating was determined by observation of the perineal sex skin and the pattern of plasma estradiol in the periovulatory period. STS-557 (0.4 mg) was administered 6 h after the initiation of mating, which was continued for an additional 42 h. Controls received an empty gelatin capsule in the same mating protocol. Conception rate in the control baboons (n = 20) was 25%; in the STS-557-treated baboons (n = 18) it was 22%. There was also no difference in the pattern of plasma estradiol and progesterone in control vs. treated baboons, either in pregnant or in nonpregnant animals. All pregnancies were normal. In light of the earlier report of effective postcoital action in the baboon from a single administration of STS-557 after a breeding period limited to 6 h, the effect of a single dose apparently is brief, and may not be clinically useful.