Evidence for cleavage of [26-14C]cholesterol side-chain by human foetal membranes in vitro.

With a view to establish the hitherto undescribed role of cholesterol in foetal-membranous steroidogenesis, homogenates of term chorion pars reflexa and amnion pars reflexa and pars placentaris collected from 6 women after spontaneous labour at term (38 to 41 weeks gestation) were incubated with [26-14C]cholesterol. Using reverse-isotope dilution analysis, [14C]isocaproic acid was isolated and characterized. This conversion constitutes strong evidence that C-20, 22-desmolase activity, normally present in the adrenal, gonadal and placental tissues, is present in the homogenates of both membranes. The efficiency of the enzymic conversion suggests that the chorion possesses a more active desmolase system compared to that of the amnion.