Time-studies of the changes in the sex-dependent activities of enzymes of hepatic steroid metabolism in the rat following gonadectomy.

The activities of cytoplasmic 3 alpha- and 17 beta-hydroxysteroid dehydrogenase, microsomal 3 alpha- and 3 beta-hydroxysteroid dehydrogenase and microsomal 5 alpha-reductase of rat liver were determined at different time points after gonadectomy on day 75 of life. Following testectomy the activities in male rats assume female values. However this change is relatively slow, 10--14 days being necessary for significant trends in individual activities to develop, and 40--60 days before the final level of activity is reached. The changes in enzyme activities after ovariectomy are only slight. The change in microsomal 5 alpha-reductase activity following gonadectomy of male rats is biphasic, the activity increasing initially to the normal female level before falling to the intermediate "neonatally androgen-imprinted" level. The reaction of 17 beta-hydroxysteroid dehydrogenase activity to testectomy and ovariectomy indicates that in the course of several years, during which we have investigated the behaviour of this enzyme in Chbb/THOM rats, the regulation of its activity has changed from one of oestrogen dependency to one of androgen dependency.