Plasma Androgen Concentrations in Several Species of Old and New World Monkeys

Abstract

The concentration of unconjugated testosterone in peripheral blood plasma of adult male (14 kg) rhesus macaques was about 50% greater than that in plasma of adult male humans. The testosterone concentration in sexually immature monkeys (early adolescence, 5 kg) is of the order of 1/10 the adult level. In immature rhesus the ratio of testosterone to androstenedione was less than 1, whereas it was 3 or more in adult animals. The percentage binding of testosterone to proteins as measured by equilibrium dialysis with plasma diluted 1:5 was 96.2 % in mature animals; it was significantly (p<0.01) greater in immature rhesus (98.0%). On the other hand, maturation had no effect on the percentage binding of androstenedione anddehydroepiandrosterone. Despite the slight difference in testosterone binding between the 2 age groups, it would not appear that the large changes in androgen concentrations during sexual maturation of rhesus are due to changes in percentage binding to plasma proteins. Androgen concentrations and percentage binding have also been determined in spider monkeys, baboons, squirrel monkeys, capuchin monkeys and cynomolgus macaques. In those of the nonmacaques which were probably adult, the testosterone concentration tended to be higher than in humans and rhesus. Percentage binding of androgens varied but was consistent within a given species. (Endocrinology85: 941, 1969)