The in vitro metabolism of radioactive progesterone and testosterone by the gonads of the protandrous Rhabdosargus sarba at various sexual phases.

The in vitro steroidogenic capacity of the gonadal tissue in the protandrous Rhabdosargus sarba was studied. Testicular and ovarian tissues from various sexual phases were used either separately or combined. With progesterone as precursor, high yield of 5 beta-reduced metabolites, and no 11-ketotestosterone or 11 beta-hydroxytestosterone were found. The production of 5 beta-pregnan-3 alpha-ol-20-one and 5 beta-pregnane-3,20-dione was very high in incubations with testicular tissue from intersexes or males and was low in those with ovarian tissue only. The production of 17 alpha-hydroxyprogesterone was high in the female but was low in other sexual phases. With testosterone as precursor, 11-ketotestoterone and 11 beta-hydroxytestosterone were identified. The latter was the most abundant and prominent polar steroid in all incubations. 5 beta-Reductase activity was high in the male and relatively low in the female. 5 alpha-Reduced products, however, were absent. There was an increase in the production of androstenedione as the animal underwent sex reversal. The significance of this change in steroidogenesis in this protandrous fish is at present under investigation. Experimental results also indicated that in the intersexual gonad there may be interaction between the testicular component and the ovarian component in steroidgenesis.