INCORPORATION OF ACETATE-1-C14INTO TESTOSTERONE AND 3β-HYDROXYSTEROLS BY THE CANINE TESTIS1

Abstract

Acetate-1-C¹⁴ was infused into the spermatic arteries of dogs at a constant rate before and after human chorionic gonadotropin was injected into the spermatic circulation to one testis. The blood from the spermatic vein was collected and the amounts and specific radioactivities of testosterone in successive samples were determined. In several experiments gonadotropin-stimulated and unstimulated testes were removed at the end of the collection, the various particulate fractions separated by high speed centrifugation and the specific activity of the digitonin-precipitable material in each determined. The specific activity of the testosterone rose very soon after the introduction of the gonadotropin. In most cases the output of testosterone also increased, but even in those cases where this did not occur the specific activity was higher. The pool of intermediates between acetate and testosterone, therefore, seemed to be quite small in the actively secreting testis and the point of action of human chorionic gonadotropin appeared to be before the rate limiting step in testosterone biosynthesis. There was no correlation between the specific radioactivity of the various digitonin-precipitable fractions and that of testosterone before and after gonadotropin. The specific activity of the testosterone after the gonadotropin injection was always higher than any digitonin precipitable fraction, and in most cases this was true before gonadotropin injection. If cholesterol is an obligatory intermediate in the biosynthesis of testosterone in the testis, the pool involved is only a minor portion of any of the fractions separated.