The skin of the male African catfish, Clarias gariepinus: A source of steroid glucuronides

Abstract

Steroid metabolism in the skin of mature male African catfish, Clarias gariepinus, reared in the laboratory, was studied in vitro by tissue incubations with [3H]pregnenolone, [3H]dehydroepiandrosterone, [3H]17α-hydroxyprogesterone, [3H]androstenedione, [14C]11β-hydroxyandrostenedione, and [3H]testosterone as precursors. While pregnenolone was not converted to any other steroid, dehydroepiandrosterone was transformed mainly to 5-androstene-3α, 17α-diol. The products of 17α-hydroxyprogesterone incubations were 5β-pregnane-3α, 17α-diol-20-one, 5β-pregnane-3α,17α, 20β-triol, and 5β-pregnan-17α-of-3,20-dione. The major steroids of androstenedione incubations were etiocholanolone, testosterone, and androsterone. Testosterone was converted mainly to etiocholanolone and androstenedione, and only small quantities of 11β-hydroxytestosterone, 11-ketotesterone, and 11-ketoandrostenedione were the metabolites found in 11β-hydroxyandrostene-dione incubation. These results demonstrated the presence of the enzymes 5α- and 5β-reductases and 3α-, 11β-, 17β-, and 20β-hydroxysteroid dehydrogenases in the skin. From enzymehistochemical results it appeared that the steroid conversions take place in the epithelial cells. Moreover, the presence of UDP-glucose dehydrogenase, an enzyme involved in the synthesis of glucuronic acid, in these cells indicates the possibility of steroid glucuronide formation. Indeed significant amounts of water-soluble steroid conjugates, particularly 5β-dihydrotestosterone- and testosterone-glucuronide, were found in the incubations with androstenedione and testosterone, indicating the presence of the UDP-glucuronosyl transferase in the catfish skin. In the light of these results, a role of the skin of African catfish in the production of semiochemicals having pheromonal properties is discussed.