A study of 5 alpha-reductase in human fetal brain

To study 5 alpha-reductase activity in the human fetal tissues, hypothalamus, cerebrum, skin, liver, kidney, small intestine, lung, adrenal and placenta of aborted fetuses at mid gestation were obtained and incubated with labeled delta 4-3-keto steroids under CO gas in the presence of excess NADPH. A higher conversion of progesterone to 5 alpha-pregnanedione was observed in the hypothalamus and cerebrum than in other tissues studied. The major portion of 5 alpha-reductase in the cerebrum was localized in 800 X g precipitate (crude nuclear fraction). Androstenedione and progesterone were found preferred substrate for 5 alpha-reductase to 17 alpha-hydroxyprogesterone or testosterone. Km of 5 alpha-reductase for progesterone and androstenedione were 1.0 X 10(-5) M and 9.0 X 10(-6) M, respectively. The enzyme activity for progesterone was inhibited by estrone and androstenedione but not by estriol.