SEXUAL-MATURATION IN MALE RHESUS-MONKEYS - IMPORTANCE OF NEONATAL TESTOSTERONE EXPOSURE AND SOCIAL RANK

In a 5-year longitudinal study, we examined the effect of disrupting t he neonatal activity of the pituitary-testicular axis on the sexual de velopment of male rhesus monkeys. Animals in a social group under natu ral lighting conditions were treated with a GnRH antagonist (antide), antide and. androgen, or both vehicles, from birth until 4 months of a ge. In antide-treated neonates, serum LH and testosterone were near or below the limits of detection throughout the neonatal period. Antideandrogen-treated neonates had subnormal serum LH, but above normal tes tosterone concentrations during the treatment period. From 6 to 36 mon ths of age, serum LH and testosterone were near or below the limits of detection. Ten of 12 control animals reached puberty during the breed ing season of their 4th year, compared with five of 10 antide- and thr ee oi eight antide+androgen-treated animals. Although matriline rank w as balanced across treatment groups at birth, a disruption within the social group during year 2 resulted in a marginally lower social ranki ng of the two treated groups compared with the controls. More high (78 %) than low (22%) ranking animals reached puberty during year 4. Durin g the breeding season of that year, serum LH, testosterone and testicu lar volume were positively correlated with social rank. Thus the lower social rank of treated animals may have contributed to the subnormal numbers of these animals reaching puberty during year 4. However, of t hose animals achieving puberty during year 4, the pattern of peripuber tal changes in serum testosterone and testicular volume differed betwe en control and antide-treated animals. The results appear to suggest t hat the disruption of normal activity of tile neonatal pituitary testi cular axis retarded sexual development, but that social rank is a key regulatory factor in setting the timing of sexual maturation in male r hesus monkeys. The effect of neonatal treatment with antide and low so cial rank on sexual development could not be reversed by neonatal expo sure to greater than normal concentrations of androgen.