The differential regulation of the intranuclear progestin in mouse kidney and prostate-seminal vesicles.

This study was designed to confirm the identity of the enzyme involved in the appearance of a nuclear metabolite of 6a-methyl progesterone (6MP) in mouse kidney but not in prostate-seminal vesicle. 6MP and progesterone competed for metabolism by the kidney enzyme. Using progesterone as substrate, the results of recrystallization of the product with 20a-hydroxy progesterone supported the identification of the enzyme as 20a-hydroxysteroid dehydrogenase (20aHSD). The enzyme had a substrate specificity similar to that reported for 20aHSD in other tissues. Renal enzyme activity was higher in female than in male CD-1 mice while activity was generally lower and without a sex difference in a random bred colony. Renal enzyme activity varied slightly with the estrous cycle, being highest at proestrus and lowest on day 2 of diestrus. Little enzyme activity was detected in prostate-seminal vesicles. It appears that 20aHSD is an important factor in regulating the differential presence of the 20a-metabolite of 6MP in kidney and prostate-seminal vesicle nuclei.