Age Related Changes in Serum Levels of Gonadotropins and Testosterone in Infantile Male Rhesus Monkeys1

The developmental patterns of gonadotropin and testosterone levels in serum were studied in 6 male monkeys bled at frequent intervals for the first several months after birth. Serum luteinizing hormone (LH) levels were measured using an in vitro bioassay (the rat interstitial cell-testosterone assay; RICT) and, in some instances, a radioimmunoassay. Follicle stimulating hormone (FSH) and testosterone were measured by immunoassay alone. Serum concentrations of testosterone, FSH and biologically active LH were elevated during the first 3–4 months of life in all 6 animals studied. Thereafter, circulating concentrations of these hormones declined to relatively low or undetectable levels. Thus, the results of this study demonstrate that the hypophyseal-testicular axis of the male monkey is quite active during the early neonatal period.