Pubertal endocrinology of the baboon: adrenarche.

The concentration of the adrenal steroids dehydroepiandrosterone (DHA) and dehydroepiandrosterone sulfate (DHA-S) was measured by radioimmunoassay in plasma of 134 baboons (Papio cynocephalus) from 0 to 17 yr of age. Plasma androstenedione (delta 4-A) was also measured in 289 baboons encompassing the same age range. The concentration of DHA was persistently high from birth to adulthood, exceeding 700 ng/dl at all ages. This differs markedly from the human pattern in which DHA concentrations fall below 50 ng/dl following regression of the fetal adrenal. Plasma DHA-S declined rapidly during the first 2 yr of life, causing a significant age-related decline in the ratio of DHA-S:DHA, a pattern not seen in man. Plasma delta 4-A declined during the first 3 yr, but remained greater than 100 ng/dl. delta 4-A then rose sharply at age 4, the time of gonadal maturation in the baboon. Thus, the baboon differs from man primarily in the persistent elevation of plasma DHA and delta 4-A prior to puberty. It remains to be determined whether this difference reflects fundamentally different mechanisms regulating adrenal androgen secretion or merely the closer temporal juxtaposition of fetal adrenal regression and adrenarche due to the more rapid sexual maturation of the baboon.