The effects of diethylstilbestrol (DES) before birth on the development of masculine behavior in juvenile female rhesus monkeys

Eight pregnant rhesus monkeys were injected with 100 /Lg diethylstilbestrol dipropionate (DESDP) from the 40th day of gestation until term, a long-term treatment. Male (n = 3) and female (n = 5) offspring were obtained. Five other pregnantfemales were injected with DESDP begin­ ning on the 115th day of gestation and continuing until either the 140th day or term-a relatively short-term treatment. Five female infants were obtained from these short-term treatments. Monkeys from the treated preg­ nancies were assigned randomly to mother-infant social groups containing untreated male and female infants the same age. They were observed in their peer groups each weekday from 3 to 12 months of age, and the display of mounting and play behavior was recorded for each subject. Results showed that DESDP significantly in­ creased the frequency of display of these juvenile behav­ iors only in long-term-treated females. However, one of the aspects of mounting that is characteristic of males (the ratio of complete to abortive mounts) was unaf­ fected even by the long-term treatment. Thus, DESDP­ treated females displayed a Iimited behavioral masculini­ zation. Whether this limitation was due to dosage and/ or timing or to a selective action of DESDP was not de­ termined. DESDP-treated males were not altered in any measurable way compared to untreated males. © 1996 Academie Press