Steroid metabolism in the testes of the breeding and nonbreeding three-spined stickleback, Gasterosteus aculeatus.

Steroid metabolism in the testes of sticklebacks was studied in vitro by tissue incubations with [3H]pregnenolone or [3H]androstenedione as precursors. In males in full reproductive condition (nesting), [3H]pregnenolone was mainly converted via progesterone and 17 alpha-hydroxyprogesterone into androstenedione, 11 beta-hydroxyandrostenedione, and 11-ketoandrostenedione. The latter was the largest product formed. The main products from the [3H]androstenedione incubation, 11 beta-hydroxyandrostenedione and 11-ketoandrostenedione, confirm these findings. The rate of androgen synthesis, especially of 11-ketoandrostenedione, was much lower after the end of the breeding season.