Developmental pattern of testosterone production by the rat testis.

We studied the steroidogenic activity of isolated Leydig cells derived from rats on fetal day 19 (F19) and postnatal (N) days 1, 12, 24, 34, 45 and adults. Leydig cells, isolated at all ages by the collagenase method, increased in number throughout development with a doubling time of 8 days. Testicular content and serum concentrations of testosterone showed parallel changes during development. Moderate values were found at the early stages (F19 and N1), with a nadir on day 12, followed by a progressive increment to reach maximal values in adulthood. A reduction in steroidogenic activity of the testis during neonatal life was confirmed by in vitro studies with isolated Leydig cells. Maximal activity was found in group F19; testosterone production diminished after birth to reach a minimum in group N34 and rose thereafter to adulthood. Leydig cells were responsive to hCG stimulation at all ages in the following order: N1 greater than N34 greater than F19 greater than N24 greater than N45 greater than adult. The present study demonstrates the existence of an active and hCG-responsive population of Leydig cells in the rat testis from fetal life to adulthood.