Summary. Plasma testosterone, 5α-dihydrotestosterone (DHT), Δ4-androstenedione, dehydroepiandrosterone (DHA) and oestradiol-17β concentrations of crab-eating macaques after birth were analysed by RIA.
The profiles of plasma testosterone and DHT exhibited four phases: (1) a neonatal phase (0 to 3–4 months of age) with considerable synthetic testicular activity; (2) a phase of 'infancy' (generally up to 29 months of age) during which the values of both androgens were low; (3) a prepubertal phase (generally up to 43 months of age) when circulating values oscillated with wider individual variations, and (4) a pubertal phase when the concentrations increased in parallel and concomittantly with the onset of meiosis and the establishment of spermatogenesis. The testosterone values continued to increase, reaching adult values at about 5–6 years of age, whereas DHT levels tended to stabilize from 4–5 years. Relatively high androstenedione values during the neonatal phase decreased progressively until puberty, then increased again slowly up to the adult stage when they plateaued at about neonatal levels. The DHA levels were high during the first months, decreased at about 1 year, remained stable during infancy and prepuberty and then declined again during puberty. At about 5 years, the values were 28% of those in neonates. There was no evidence of an adrenarche before the first signs of sexual maturity were observed. Oestradiol-17β concentrations were high at birth and until 3 months, then decreased and remained steady from 1 year of age until adulthood, except at the onset of puberty (27–30 months of age) when high values were again noted.
Our results show that, during the neonatal period, the testis exhibited considerable secretory activity.