Effects of prenatal antiandrogen treatment on masculinization and defeminization of guinea pigs.

Gonadectomized (gdx) guinea pigs which had received the antiandrogen flutamide prenatally were tested for female-typical and male-typical sexual behavior in adulthood. In tests for lordosis behavior, gdx males and females were injected with estradiol benzoate and progesterone. Prenatally flutamide-treated females showed a longer mean lordosis response than control females. This was true whether they were given either a high or a low dose of EB. No male ever showed a lordosis response. In tests for male-typical sexual behavior, gdx adult males were treated with testosterone propionate and tested with stimulus females. The prenatally flutamide-treated males showed significantly decreased levels of ejaculation, a lower intromission rate and a decreased percentage of mounts which included pelvic thrusts, when compared to control males. Mount rate and rate of pericopulatory behavior did not differ between the flutamide and control males. The fact that prenatal administration of flutamide increased female-typical behavior in adult females suggests that the female guinea pig is normally partially defeminized by androgens in utero. The male guinea pig appears to be resilient to attempts to block defeminization with prenatal antiandrogens. However, some aspects of masculinization can be blocked.