Progesterone metabolism in the microsomal fraction of the testis, head kidney, and trunk kidney from the rainbow trout

Abstract

In the present study on male rainbow trout, well-defined microsomal fractions from gonad, trunk kidney, and head kidney were used to study enzymes active on progesterone. The metabolites produced were identified by mass spectrometric analysis. In the testis the main metabolite was 17α-hydroxyprogesterone which is an intermediate in the steroid biosynthetic pathway. 17α-Hydroxyprogesterone was also identified in incubations from head and trunk kidney. The 17α-hydroxylase activity was higher in the head kidney than in the trunk kidney which probably reflects the presence of steroid producing interrenal cells in this part of the kidney. The conversion of progesterone to 17α-hydroxylated products in the testis and head kidney was NADPH dependent and inhibited by carbon monoxide, indicating the participation of cytochrome P450 monooxygenase in this reaction. NADH supported the reaction to some extent (27% of the NADPH-dependent activity) in the testis but not in the head kidney. In addition to 17α-hydroxyprogesterone the head and trunk kidney microsomes gave rise to 16α- and 6β-hydroxyprogesterone. These activities were low or absent in testis microsomes. Progesterone 5α-reductase activity was only detected in trunk kidney microsomes.