INVOLVEMENT OF STEROID HORMONES IN GONADOTROPIN-INDUCED TESTICULAR MATURATION IN MALE JAPANESE EEL (ANGUILLA JAPONICA)

In the cultivated male Japanese eel, spermatogonia are the only germ cells present in the testis. Five weekly injections of human chorionic gonadotropin (HCG) induced spermatogenesis and spermiogenesis. This was accompanied by a marked increase in serum levels of ll-ketotestosterone and testosterone; the increase in the former was much greater than that of the latter. These results suggest that the action of HCG in inducing testicular development in male eel is mediated by the production of ll-ketotestosterone in the testis. Despite the appearance of spermatozoa in the testis, HCG injections produced very little milt. Serum levels of 170:,20,6’-dihydroxy-4-pregnen-3-one (l7a,20[i’-DP), a steroid which has been shown to be effective in inducing oocyte maturation and spermiation in several teleosts, remained very low throughout the period of HCG treatment. However, in virro incubation studies showed that HCG-treated testes were able to convert exogenous 17a-hydroxyprogesterone to l7a,20[>’-DP, indicating that these testes possess 20,6’-hydroxysteroid dehydrogenase. Injections of 17a, 20/1°-DP to these males significantly raised milt volume and decreased spermato-crit values. l7a,20,8-DP injections also markedly increased the percentage of motile sperm and the duration of sperm motility, concomitant with a significant increase in the pH of the sperm duct, but not that of the testis. Taken together, these results suggest that l7a,20,8-DP plays an important role in inducing final testicular maturation and sperm motility in male eel, the latter action of the steroid being mediated probably through an increase in the sperm duct pH. It is concluded that incomplete testicular and sperm maturation by HCG injections is due in part to the failure of the testis to produce l7cx,20[>’-DP in response to HCG stimula-tion.