Responsible for the reduction of the oxo group on the C-3 of 5alpha-androstane steroids. Catalyzes the conversion of dihydrotestosterone to its inactive form 5alpha-androstanediol, that does not bind androgen receptor/AR. Does not function as an isomerase. a 3beta-hydroxysteroid + NADP(+) = a 3-oxosteroid + H(+) + NADPH 5alpha-androstane-3beta,17beta-diol + NADP(+) = 17beta-hydroxy-5alpha-androstan-3-one + H(+) + NADPH Steroid metabolism. High levels in adrenal gland, kidney and male liver (at protein level). Low levels in female liver (at protein level). Expressed in ovaries (at protein level). Belongs to the 3-beta-HSD family.