Sex Dependency of Steroid Retention in Rat‐Liver Slices Incubated with Testosterone

The hepatic retention of steroids which occurs during the incubation of [4‐ 14 C]testosterone with rat liver slices is demonstrated to be a sex‐specific phenomenon. After an incubation time of 30 min, slices from female animals can be shown to have retained significantly more [4‐ 14 C] steroid than slices from male animals. The tissue/medium distribution ratio is 13 for the males and 30 for the females. Δ 4 ‐5α‐Hydrogenase activity of the liver tissue can be regarded as the driving force for the retention of steroids derived from testosterone turnover. Namely, the steroid retention is positively correlated with the testosterone hydrogenation rate. The Δ 4 ‐hydrogenating activity of the female exceeds that of the male by a factor of 1.73; this is the same factor by which the hepatic retention of the female exceeds that of the male. In contrast, there is an inverse correlation between the production rate of hydroxylated C 19 O 2 ‐metabolites and the extent of retention. When compared to the female animal, slices from the male possess a higher hydroxylating activity accompanied by a much lower retention. The majority of metabolites isolated from tissue have a retention which is proportional to their production rate; however, the proportionality factor varies from metabolite to metabolite. Thus, for each individual metabolite, the slice is able to maintain a specific concentration gradient against the medium. For these metabolites the retention is sex‐specific only in so far as their production rate is sex‐specific. The retention of testosterone and androstenedione is independent of their production rate. They are found in the incubation medium of both sexes, but only in the tissue of males.