Production of estradiol by the fetal rat testis

Testes from 17- to 20-d-old rat fetuses were cultured in vitro for various time intervals in Medium 199 alone or with added gonadotrophins. Estradiol released into the culture media was determined by radioimmunoassay. A basal estradiol secretion rate was inexistant or undetectable at all stages studied. In early stages (17 and 18 d) there was no difference in the stimulatory effect of FSH or LH at the same concentration. At 19 d, the prevalence of FSH became apparent. At 20 d, a significant action of FSH was noted after only 3 h culture time. 1-Methyl-1, 4-androstadiene-3,17-dione, an aromatase inhibitor, markedly depressed FSH-stimulated estradiol secretion. In the 20-d old testis, stimulation of estradiol production by FSH was more rapid and reached a higher level than by (Bu)2cAMP. It is suggested that the difference in the action of LH and FSH reflects the difference in the time of appearance of the corresponding receptors in the developing fetal testis.