Steroid metabolism in fetal tissues. III. Conversion of testosterone to 5alpha-dihydrotestosterone in human fetal gonads.

Testes and ovaries of 25 human fetuses obtained between the 17th--40th week of gestation were examined in vitro for 5alpha-reductase activity by a double isotope method. In 14 fetal testes, conversion of testosterone to 5alpha-dihydrotestosterone ranged between 1.04 to 4.26% (2.80% +/- 0.31 SEM) and in 11 fetal ovaries a conversion rate of 0.20 to 2.91% (1.09% +/- 0.22 SEM) was found. The difference was statistically significant (p less than 0.001). This was also confirmed by studying the gonads of twins. The data support previous studies indicating that human fetal testes and ovaries are different in their steroid metabolic activities. Age dependency could not be demonstrated.