A Study of 5α-Reductase in Human Fetal Brain

Abstract

To study 5α-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 Δ⁴-3-keto steroids under CO gas in the presence of excess NADPH.
A higher conversion of progesterone to 5α-pregnanedione was observed in the hypothalamus and cerebrum than in other tissues studied. The major portion of 5α-reductase in the cerebrum was localized in 800×g precipitate (crude nuclear fraction). Androstenedione and progesterone were found preferred substrate for 5α-reductase to 17α-hydroxyprogesterone or testosterone. Km of 5α-reductase for progesterone and androstenedione were 1.0×10^-5 M and 9.0×10^-6 M, respectively. The enzyme activity for progesterone was inhibited by estrone and androstenedione but not by estriol.