Steroid production by amago salmon (Oncorhynchus rhodurus) testes at different development stages

Developmental changes in the steroidogenic capacity of amago salmon (Oncorhynchus rhodurus) testicular fragments at six different stages during spermatogenesis and spermiation were examined using 18-hr incubations. Although both basal and chum salmon gonadotropin (SGA)-induced production of 11-ketotestosterone (11-ketoT) and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta-diOHprog) remained relatively low in testicular fragments isolated in August (GSI 1.06; primarily spermatocytes and spermatids in the testes) and September (GSI 2.33-4.85; many spermatids and spermatozoa in the testes), 11-ketoT production was two to three times higher than 17 alpha,20 beta-diOHprog production. In mid October (GSI 4.31; primarily spermatozoa in the testes, with a few spermatids remaining), SGA greatly stimulated 11-ketoT production with no further stimulation in late October (GSI 3.54; advanced spermiation). In contrast, SGA dramatically increased 17 alpha,20 beta-diOHprog production in late October and November (GSI 3.02), coincident with the period of active spermiation. A time course study showed that SGA caused a marked increase in production of 17 alpha,20 beta-diOHprog within the first 3 hr. Testes collected in August and September produced a considerable amount of 17 alpha,20 beta-diOHprog in the presence of an exogenous precursor, 17 alpha-hydroxyprogesterone. These results indicate that a shift in steroidogenesis from 11-ketoT to 17 alpha,20 beta-diOHprog occurs in the amago salmon testis immediately prior to or during the spermiation period and further suggest that mechanisms of gonadotropin action on 17 alpha,20 beta-diOHprog production in testes differ from those of ovaries (Y. Nagahama, 1987, Dev. Growth Differ. 29, 1-12).