5 alpha-reductase activity in human fetal testis.

Human fetal testis (32-weeks-old) homogenates were incubated with [3H]pregnenolone and [3H]progesterone in the presence of cofactors. 2. Following incubation, radioactive products were separated and identified by chromatographic procedures, derivative formation and recrystallization to constant 3H/14C ratio. 3. The enzyme activity of 5 alpha-reductase in the 10,000 g supernatant was measured. 4. The fetuses' testes convert about 30% of [3H]pregnenolone mainly to [3H]androst-5-ene-3 alpha, 17 beta-diol and [3H]-3 beta-hydroxyandrost-5-ene-17-one, and none or very small amounts of 5 alpha-reduced steroids could be measured. 5. Preincubation treatment of the 10,000 g supernatant (with charcoal or with 3-hydroxysteroid dehydrogenase preparation yields DHT as one of the metabolites which was identified, and a considerable 5 alpha-reductase activity which obeyed Michaelis-Menten kinetics was measured.