Metabolism of pregnenolone in adrenal homogenates at low temperatures

Endogenous and radioactively-labelled exogenous pregnenolone was metabolized in adrenal homogenates (0.32 M sucrose, pH 6.8) of the rabbit, the cow and the ewe when kept at temperatures between 0 and+6°C. This process could be prevented by the addition of cyanoketone, an inhibitor of the enzyme 5-ene-3β -hydroxysteroid dehydrogenase complex. The activity of the enzyme at low temperatures can lead to erroneous conclusions when studying the subcellular distribution of steroids in tissues in which it is present. No metabolism of pregnenolone was observed in dog adrenal homogenates at low temperatures.