Effect of 17 beta-estradiol, testosterone, and 11-ketotestosterone on 17,20 beta-dihydroxy-4-pregnen-3-one production in the rainbow trout testis.

The principal hormone related to spermiation in Oncorhynchus mykiss is 17,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta OHP). In the present study we analyzed the possible paracrine/autocrine effects of three other testicular steroids (17 beta-estradiol, 11-ketotestosterone, and testosterone) on the synthesis and secretion of this progestin in male rainbow trout. Pieces of testis at various stages of spermatogenesis were incubated for 24 or 48 hr with one of these steroids (5 to 800 ng ml-1) either alone or with the gonadotropin GtH II. Following incubation, 17,20 beta OHP was measured by RIA in the culture media. In vitro, only 17 beta-estradiol (E2) decreased 17,20 beta OHP secretion repeatedly and significantly when doses higher than or equal to 50 ng ml-1 were used. This effect was observed mainly at the spermiating stage and under gonadotropic stimulation. In turn, E2 did not seem to modify the testicular capacity to convert 17-hydroxyprogesterone into 17,20 beta OHP. In vivo, the circulating levels of E2 decreased at the beginning of spermiation, concomitantly with an increase of 17,20 beta OHP in plasma. These in vitro and in vivo data suggest a possible role for E2 in the regulation of 17,20 beta OHP secretion by testes, in particular during the spermiating period.