SIDE-CHAIN CLEAVAGE OF 4-CHOLESTEN-3-ONE, 5-CHOLESTEN-3-ALPHA-OL, BETA-SITOSTEROL, AND RELATED STEROIDS IN ENDOCRINE TISSUES FROM RAT AND MAN

Fourteen 4-14C-labeled C27- and C29-steroids were incubated with mitochondria prepared from rat adrenals, ovaries, testes and placenta and fortified with NADPH. Of the 11 C27-steroids, 6 were available also with 26-14C-label. The main purpose was to study which of the substrates tested could be converted to C21- and/or C19-steroids. When experiments with a 4-14C- and a 26-14C-labeled steroid were run in parallel, the metabolites not labeled in 26-14C-experiments but in 4-14C-experiments, were considered as steroids containing a side-chain shorter than that of the C27-substrate. Identifications were also based on chromatography data (TLC and GLC combined with radioactivity detection). In the rat, cholesterol and .beta.-sitosterol were converted into C21- and C19-steroids in mitochondria from all tissues tested. 5-Cholesten-3.alpha.-ol was converted into the 3.alpha.-epimer of pregnenolone in the adrenal and ovarium 8500 g sediment. 4-14C-Labeled 4-cholesten-3-one was converted in the testes to labeled androstenedione, without the presence of labeled C21-steroids. Using the conditions employed in studies with testis mitochondria, adrenal 8500 g sediments were able to metabolize 4-cholesten-3-one into progesterone and 17.alpha.-hydroxyprogesterone. Other C27- and C29-steroids tested, yielded polar metabolites to different degrees. None of those metabolites was identified as a C21- or C19-steroid. Pregnenolone and progesterone were shown to be formed from cholesterol and .beta.-sitosterol in mitochondria prepared from human adrenals, testes and term placentae.