3-alpha-hydroxysteroid dehydrogenase that converts 3-alpha-tetrahydroprogesterone (allopregnanolone) to dihydroxyprogesterone and 3-alpha-androstanediol to dihydroxyprogesterone (PubMed:11294878, PubMed:29541409). Also plays a role in the biosynthesis of retinoic acid from retinaldehyde (PubMed:11304534, PubMed:12618084). Can utilize both NADH and NADPH. 3beta-hydroxy-5alpha-pregnane-20-one + NAD(+) = 5alpha-pregnane-3,20-dione + H(+) + NADH 17beta-hydroxy-5alpha-androstan-3-one + NAD(+) = 5alpha-androstan-3,17-dione + H(+) + NADH 3alpha-hydroxy-5alpha-androstan-17-one + NAD(+) = 5alpha-androstan-3,17-dione + H(+) + NADH 5alpha-androstane-3alpha,17beta-diol + NAD(+) = 17beta-hydroxy-5alpha-androstan-3-one + H(+) + NADH all-trans-retinol + NAD(+) = all-trans-retinal + H(+) + NADH 3alpha-hydroxy-5alpha-pregnan-20-one + NAD(+) = 5alpha-pregnane-3,20-dione + H(+) + NADH Homotetramer. Associated with microsomal membranes. Highly expressed in trachea and epidermis. Detected at lower levels in spinal cord, bone marrow, brain, tongue, esophagus, heart, colon, testis, placenta, lung, skeletal muscle and lymph node. Belongs to the short-chain dehydrogenases/reductases (SDR) family.