Metabolism of testosterone in vitro by brain and pituitary slices of a seawater turtle ( Chelonia mydas mydas) and a freshwater turtle ( Podocnemis expansa)

Abstract

The metabolism of [4- 14C]-testosterone was studied in the midbrain, pituitary and hypothalamus of two turtles, the Chelonia mydas mydas (sea turtle, male) and Podocnemis expansa (freshwater turtle, female). [4- 14C]-Testosterone was incubated for l h (pH 7.5, 25°C) in a Krebs-Ringer tris-buffer medium with slices of mesencephalon, pituitary and hypothalamus obtained from Chelonia mydas mydas and mesencephalon and pituitary obtained from Podocnemis expansa. After extraction of the steroids with etherchloroform, the metabolites were separated and identified by column chromatography on Sephadex LH-20, thin-layer and radio gas chromatography. The principal metabolite isolated in all incubations was 4-androstene-3,17-dione, which was identiified as free as well as methoxime derivative. A great number of metabolites were isolated in the incubations carried out with mesendephalon in both turtles. Besides 4-androstene-3,17-dione and two unidentified steroids, the following 5α-reduced steroids were isolated and identified: 5α-dihydrotestosterone, androsterone, and 5α-androstane-3α,17β-diol. These results indicate that the occurrence of 5α-reductase activity in the mesencephalon is not limited to mammalian vertebrates.