Probably involved in steroid metabolism. Catalyzes the oxidation of androsterone (3alpha-hydroxy-5alpha-androstan-17-one) and 20beta-hydroxyprogesterone (4-pregnen-20beta-ol-3-one), and the reduction of progesterone (4-pregnen-3,20-dione). Shows a preference for NADH. Has no detectable activity for oxidation of L-3-hydroxybutyric acid and only an insignificant activity for reduction of acetoacetyl-CoA. androstan-3alpha,17beta-diol + NAD(+) = 17beta-hydroxyandrostanone + H(+) + NADH 3alpha-hydroxy-5alpha-androstan-17-one + NAD(+) = 5alpha-androstan-3,17-dione + H(+) + NADH (20R)-20-hydroxypregn-4-en-3-one + NAD(+) = H(+) + NADH + progesterone kcat is 7.6 min(-1) with androsterone as substrate. kcat is 4.3 min(-1) with 20beta-hydroxyprogesterone as substrate. kcat is 1.2 min(-1) with progesterone as substrate. Optimum pH is 6.0 for reductase activity. Lipid metabolism; steroid degradation. Homotetramer (PubMed:12524453). Homodimer (PubMed:11807257). Belongs to the short-chain dehydrogenases/reductases (SDR) family.