Gonadal in Vitro Androstenedione Metabolism and Changes in Some Plasma and Gonadal Steroid Hormones during Sex Inversion of the Protandrous Sea Bass, Lates calcarifer

Abstract

Steroidogenesis in the gonad of the protandrous sea bass, Lates calcarifer, was examined in vitro in spermiating testis, previtellogenic ovary, and transitional gonads. Gonadal tissues were incubated with tritiated androstenedione. Metabolites were analyzed by thin-layer chromatography, high-performance liquid chromatography, microchemical reactions, and crystallization to constant specific activity. 17β-Hydroxysteroid dehydrogenase, 5β-reductase, and 3α-hydroxysteroid dehydrogenase activities were found in all of the sex types. On the other band, 11β-hydroxysteroid dehydrogenase and 11β-hydroxylase activities were found only when testicular tissue was present, i.e., in testis and early transitional gonad. A low aromatase activity leading to estrone synthesis was detected in the previlellogenic ovary. In late transitional gonads, a major metabolite (metabolite X) was suggestively identified as a 3-ester of 17β-estradiol according to its chemical and immunological characteristics. Levels of 17β-estradiol (E2), the metabolite X, testosterone (T), and 11-ketotestosterone (11 KT) were also measured by radioimmunoassay in plasma, before (January and February) and during (March and April) the sex inversion process. Plasma E2 was virtually undetectable (means below 25 pg/ml), although higher levels of metabolite X were found in transitional fish (485 ± 432 pg/ml in March). Throughout this period, plasma levels of T and 11KT and the androgens/estrogens ratio were significantly higher in males than in transitional fish, where these levels decreased during the sex inversion period. The level of in vitro synthesis of metabolite X was high in transitional gonads, but their concentrations were very low (0.07 ± 0.09 ng of equivalent E2/g in transitional gonads against 0.22 ± 0.37 ng of equivalent E2/g in testes and 2.16 ± 2.7 ng of equivalent E2/g in ovaries).