Manipulation of postnatal testosterone levels affects phallic and clitoraldevelopment in infant rhesus monkeys

Male primates exhibit marked elevation of circulating testosterone levels d uring the early postnatal period. The aim of this project was to test wheth er experimental manipulation of circulating testosterone levels in male and female infant rhesus monkeys affected development of the external genitali a during the first six months of life. Four groups of infants were studied. Seven control male infants exhibited high circulating testosterone levels during the first three months of life. Seven males were treated with a GnRH agonist (avorelin) from the first week of life onwards, which suppressed t he postnatal testosterone surge. Ten control :females exhibited low circula ting testosterone levels during the early postnatal period. Administration of testosterone to 10 females resulted in high circulating levels in these infants. Fortnightly blood samples and genital measurements were taken from all infants during the first six months of life. Growth of the penes of av orelin-treated males was significantly retarded when compared to control ma les. Average length of the penis at six :months of age was significantly (p = 0.012) smaller for avorelin-treated males (25.2 +/- 2.8 mm) than for con trol males (37.3 +/- 3.0 mn). Avorelin-treated males attained only around 5 0% detachment of the prepuce from the glans of the penis, while control mal es averaged 90% detachment. Treatment of females with testosterone resulted in significant growth of the clitoris in comparison to control females. Th e growth rates of the penes of control males and clitorides of testosterone -treated females were similar and greatest during the first two months of l ife. Gain in body weight was not affected by either hormonal manipulation. It is concluded that manipulation of circulating testosterone levels during the early postnatal period affects penile and clitoral development of infa nt rhesus monkeys. This postnatal period may therefore represent an importa nt stage in penile development in primates.