Adrenal 11-hydroxylase activity in a hypercortisolemic New World primate: adaptive intra-adrenal changes

The squirrel monkey, a representative New World primate, has high plasma cortisol and aldosterone concentrations when compared to Old World primates. We measured adrenal mitochondrial 11-hydroxylase (11-OHase) activity in squirrel monkeys and in two representative Old World species (cynomolgus and rhesus macaques) in an effort to explain these elevated plasma glucocorticoid and mineralocorticoid levels. The activity of 11-OHase was 5-fold higher in the squirrel monkey than in the Old World species tested. Calculated 11-OHase Vmax was different in the squirrel monkey and the cynomolgus. However, the Km values were similar in the New World primate when compared to cynomolgus. The ability of metyrapone to block 11-OHase was less in the former than in the latter. The data are consistent with the hypothesis that the squirrel monkey adrenal cortex possesses an increased number of 11-hydroxylase enzyme units compared to that of Old World primate species, and is therefore more efficient in producing cortisol. This difference in 11-OHase activity in the squirrel monkey, in addition to other previously reported adrenal steroidogenic enzyme alterations, may be adaptive in nature, favoring increased cortisol and aldosterone production in this and possibly other New World primate species.