Absence of gonadotropin-induced desensitization of testosterone production in the neonatal rat testis.

The formation of testosterone and some of its precursors (pregnenolone, progesterone, 17-hydroxyprogesterone and androstenedione) was studied in response to hCG stimulation in neonatal (5-day-old) and adult (60-day-old) male rats. Evidence for a biphasic testosterone response was observed at both ages, with a sharp increase within the first hours, and a secondary peak at 2-3 days after the hormone injection, when monitored by intratesticular and serum steroid measurements. The decreased testosterone production between the two peaks coincided in the adult animals with a marked increase of progesterone and 17-hydroxyprogesterone production, in keeping with the known gonadotropin-induced lesions of testicular androgen production. In contrast, no increase in C21-form testosterone precursors could be observed in the neonatal rat. When in vitro testicular production of cAMP, testosterone and progesterone was studied at the two ages 24 h after the hCG injection, a decrease in extracellular cAMP and testosterone but an increase in progesterone was observed in the adult testis. In the neonate, cAMP production was decreased, but testosterone production stayed high, and progesterone production increased only marginally. The present results indicate that the adult-type steroidogenic lesions following in vivo hCG stimulation, resulting in decreased testosterone production and accumulation of C21 steroid precursors, are not operative during the fetal-neonatal growth phase of rat testis Leydig cells.