Rat testicular endogenous steroids and number of Leydig cells between the fetal period and sexual maturity.

Endogenous androgens (androstenedione, testosterone, 5 alpha-dihydrotestosterone and 5 alpha-androstane-3 alpha,17 beta-diol), and some of their C21 precursors (pregnenolone, progesterone and 17-hydroxyprogesterone) were measured in rat testes between Day 18.5 of pregnancy and Day 64 postpartum, and correlated with numerical densities of Leydig cells. The latter parameter showed an early maximum on Day 19.5 of the fetal period, a nadir on Day 15 postpartum, and a gradual increase thereafter. The two dominating androgens, testosterone and 5 alpha-androstane-3 alpha,17 beta-diol, had similar levels until 15 days of age, but the 5 alpha-diol predominated thereafter. The total steroid content per Leydig cell was highest on Day 18.5 of gestation (77 ng/10(6) cells). A decline started already in utero, and reached a nadir of 5 ng/10(6) cells on Day 29. Thereafter, a slight increase occurred with advancing age. It is concluded that: The fetal testis has highest Leydig cell and endogenous steroid concentrations. A nadir in these parameters is seen 2-4 wk postpartum. The Leydig cell concentration increases around puberty on Days 40-60, but only a slight concomitant increase occurs in steroids. A sharp decline in steroid content per Leydig cell occurs during the last fetal days, but the postnatal decline of testicular steroids is due to Leydig cell loss. The new Leydig cell generation after 15 days has a persistently low steroid concentration through puberty.(ABSTRACT TRUNCATED AT 250 WORDS)