Developmental Pattern of Testosterone Synthesis by Fetal Rat Testes in Response to Luteinizing Hormone*

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Abstract
The capacity of fetal testes from rats aged 14.5-20.5 days to synthesize testosterone and respond to LH [luteinizing hormone] was studied in vitro. Synthetic capacity was measured as rate of appearance of radioimmunoassayable testosterone in the incubation medium with or without added LH. In the absence of LH, testes retained 20-25% of total testosterone synthesized. Testosterone in the medium increased with tissue weight and time of incubation and was not metabolized to other steroids. Testicular development from 14.5-20.5 days was characterized by an increased capacity to synthetize testosterone and to respond to LH. Both parameters appear on day 15.5 of gestation. Testosterone synthesis may be under gonadotropic regulation.