Effects of different steroid-biosynthesis inhibitors on the testicular steroidogenesis of the toad Bufo arenarum

Abstract.

Testis fragments from Bufo arenarum were incubated with [7(n)-³H]pregnenolone (P5), [1,2-³H]dehydroepiandrosterone (DHEA) and [1,2,6,7-³H]testosterone (T), and different steroid-biosynthesis inhibitors. The inhibitors used were: cyanoketone (CNK), spironolactone (SPNL) and finasteride (FIN). CNK significantly increased the recovery of 3β-hydroxy-5-ene steroids while SPNL reduced the metabolism of P5 and the production of C19-steroids. The metabolism of C19-substrates was only modified by CNK, which reduced the transformation of DHEA without modifying the metabolism of T. To determine the degree of inhibition exerted by the inhibitors used, the activities of the enzymes were estimated as the percentage of their contribution to the total steroid metabolism. CNK strongly inhibited the activity of hydroxysteroid dehydrogenase/isomerase if its contribution was estimated using both P5 and DHEA. If the analysis was made considering both activities associated to cytochrome P450 17α-hydroxylase, C17–20 lyase (P450_c17), it became evident that SPNL inhibited both of them. The percent contribution of 17β-hydroxysteroid dehydrogenase (17βHSD) activity diminished in the presence of CNK only if it was estimated considering P5 and DHEA metabolism. SPNL produced a significant inhibition of 17βHSD when its contribution was estimated considering P5 metabolism. However, SPNL was insufficient if DHEA or T were considered. The effect of SPNL on the contribution of 17βHSD could be due to the reduction of C19-substrates. The activity of 5α-reductase was inhibited by CNK only if results from P5 and DHEA were considered.