Seasonal changes in the activity of 11 beta-hydroxysteroid dehydrogenase in toad testes

In mammals, glucocorticoids (GC) are inactivated by the oxidative activity of 11beta-hydroxysteroid dehydrogenase (11beta-HSD). To study that mechanism in the testes of Bufo arenarum, 11beta-HSD activity and plasma corticosterone (B) were determined in toads from pre- (PR), post- (P), and reproductive (R) periods. Toad 11beta-HSD is NAD(+)-dependent and strongly inhibited by glycyrrhetinic acid. V(max) is higher in the P period (1.37 vs. R: 0.13 and PR: 0.26 pmol/min-mg protein), whereas K(m) values (around 200 nM) remain constant. Plasma B concentrations (R: 178; PR: 61; P: 114 nM) are close to K(m) values, suggesting that, under baseline conditions, 11beta-HSD could protect testes against GC action.