Rhesus monkeys, if pregnant with a daughter fetus and if injected with testosterone during a critical period, give birth to a baby with female internal reproductive organs (two ovaries, uterus, and fallopian tubes) and male external reproductive organs (a well-developed empty scrotum and a clitorine penis). These masculinized female (hermaphroditic) monkeys have been extensively studied over the last twenty years by various researchers in different laboratories.
Prenatal androgen does not render such monkeys acyclic, as it does the female rat. There is, however, a delay in menarche associated with prenatal androgen, though subsequent ovarian function can be entirely normal and ovulation occurs. Whether the incongruency between rodents and primates on this variable is due to timing, dosage, or species differences is not known. Possibly there is a mechanism in the primate that protects the brain-pituitary systems which regulate ovulation from the damaging effects of steroid hormones present in fetal life.
The behavior of masculinized female monkeys resembles that of normal male monkeys and deviates from that of normal female monkeys. Specifically, masculinized females in the juvenile period resemble males in frequency of mounting and thrusting behavior, rough-and-tumble play, and threat and dominance behavior. Only those androgenized females whose mothers have been injected with testosterone for a long period during gestation persistently retain the spontaneous display of mounting behavior through adolescence. However, when hermaphroditic females are ovariectomized in adulthood and injected with testosterone, they mount stimulus females and can even achieve intromission and the equivalent of ejaculation with emission. Apparently, the degree of behavioral masculinization in rhesus monkeys depends in part on the total duration and amount of fetal exposure to androgen. Although prenatal exposure to androgen is one variable associated with masculinized behavior, it is not the only one. Goldfoot, in a review of the literature on nonhuman primate (primarily rhesus) sexual behavior, makes it clear that the expression of sexual behavior is determined by an intricate and as yet unexplained balance of hormonal and social environmental variables which act throughout the animal’s life cycle.
There has not yet been reported in primates a counterpart to the XY male rat fetally de-androgenized by the antiandrogen, cyproterone acetate. In human beings, however, there are several syndromes of fetal deandrogenization and of androgenization as well. In the interest of space, only two syndromes, the adrenogenital syndrome and the androgen-insensitivity syndrome will be used here, since they illustrate all of the principles involved.