Summary. Pregnant guinea-pigs were given cyproterone acetate intramuscularly from the 15th to the 40th day post coitum (p.c.). The dose for each group was 50, 75 or 100 mg/kg/day. On the 46th day p.c., the fetuses were removed and the internal and external genitalia of the genetically female guinea-pigs were examined. Virilization effects were seen in all the female fetuses examined ; there was stimulation of the epididymal tubules, development of the Wolffian ducts and prostate, but no stimulation of the seminal vesicles. There was distinct virilization of the external genitalia; the vagina was considerably shortened in favour of the sinus urogenitalis. The balanopreputial fold was completely closed over in some animals, resembling that normally found in the external genitalia of male guinea-pig fetuses. It was not possible to influence the differentiation of the gonads or the Müllerian ducts. These effects were not dose-dependent, and it was not possible to reach any conclusions about this paradoxical masculinizing action of cyproterone acetate, although a number of possible explanations are discussed.
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Gräf et al. (1974) studied this question.