Synthesis of 17,20alpha/beta-dihydroxy-4-pregnen-3-one and 5beta-pregnanes in spermatozoa of primary and 17alpha-methyltestosterone-induced secondary male grouper (Epinephelus coioides).

The in vitro metabolism of [3H]17-hydroxyprogesterone by spermatozoa of primary and 17alpha-methyltestosterone (MT)-induced secondary male grouper (Epinephelus coioides) has been examined. With only the labeled precursor, the four predominant 5beta-pregnanes (17, 20alpha-dihydroxy-5beta-pregnan-3-one; 5beta-pregnan-3alpha,17, 20alpha-triol; 3alpha,17-dihydroxy-5beta-pregnan-20-one; and 17hydroxy-5beta-pregnan-3,20-dione) accounted for 75% of the total product yield, with the remainder comprising 17, 20alpha-dihydroxy-4-pregnen-3-one (17,20alphaP) and traces (3%) of 17,20beta-dihydroxy-4-pregnen-3-one. This is the first report of the synthesis of these 5beta-pregnanes by teleost spermatozoa. The addition of excess unlabeled precursor caused a marked shift to the synthesis of only 17,20alphaP. The steroidogenic profile in spermatozoa of the primary and secondary males appears similar in both cases. The shift to 17,20alphaP synthesis at high substrate concentration may suggest a gonadotropin (GtH) control of 17, 20alphaP synthesis, involving the competition for 17P between the high-activity, low-capacity 5beta-reductases and the low-activity, high-capacity 20alpha-HSD. Poor spermiation in MT-induced males may thus be due to the lack of 17P arising from low GtH secretion in vivo in the secondary males.