Expression of Neural 5α-Reductase Messenger Ribonucleic Acid: Comparison to 5α-Reductase Activity during Prenatal Development in the Rat*

Abstract

The present study was designed to characterize the developmental pattern of 5.alpha.-reductase messenger RNA (mRNA) levels and ezyme activity in intact medial basal hypothalamic (MBH) and preoptic area (POA) tissue fragments of rats during fetal development. 5.alpha.-Reductase activity was determined using [3H]testerone as the substrate and quantifying, by TLC, the radiolabeled 5.alpha.-reduced metabolites (dihydrotesosterone [DHT] and 5.alpha.-androstane-3.alpha. 17.beta.-diol). Confirmation of the identity of the [3H]5.alpha.-DHT formed was demonstrated by recrystallization of the derivatized DHT to constant specific activity. Under saturating substrate conditions(1.7 .mu.M testosterone), there were no significant sex differences (male vs. female) detected in neural 5.alpha.-reductase during prenatal, perinatal, or neonatal development. 5.alpha.-Reductase activity was low but detectable at gestational day (GD) 15 (.apprxeq.10 pmol/h .cntdot. mg protein), increased over 3-fold to peak levels at GD 18, and then declined to moderate levels at GD 22 (.apprxeq.22 pmol/h .cntdot. mg protein) and 4 days after birth (.apprxeq.17 pmol/h .cntdot. mg protein). In addition, the developmental pattern of 5.alpha.-reductase mRNA expression in fetal MBH-POA tisue was determined by RNA blot hybridization, using a complementary DNA encoding the rat 5.alpha.-reductase enzyme. A single mRNA species was detected at 2.5 kilobase in MBH-POA tissue, which is similar in size to adult rat liver and prostate 5.alpha.-reductase mRNA. At GD 15, 5.alpha.-reductase mRNA was clearly detectable; the abundance increased on GD 17, remained at maximal levels at GDs 18, 19, and 20, and the decreased to moderate levels on GD 22. A correlation calculated between the normalized 5.alpha.-reductase mRNA levels and enzyme activities revealed a strong correspondence between mRNA abundance and enzyme activity values during prenatal development, r = 0.80, P = 0.056. These findings indicate that neural 5.alpha.-reductase activity may be developmentally regulated, and that the changes in 5.alpha.-reductase activity in MBH-POA tissue during late fetal development are regulated, in part, by the levels of mRNA encoding the 5.alpha.-reductase enzyme.