Biopotency and site of action of drugs affecting testicular steroidogenesis.

The effect of etomidate (an anaesthetic), epostane (WIN 32729; an inhibitor of ovarian and adrenal steroidogenesis) and cyproterone acetate (an antiandrogen) on testosterone secretion from mouse Leydig cells stimulated with LH (5 i.u./l) was tested. The concentration of drug which inhibited testosterone secretion by 50% was 11.5 +/- 1.1 (S.E.M.) mumol/l for cyproterone acetate, 1.2 +/- 0.2 mumol/l for etomidate and 0.23 +/- 0.03 mumol/l for epostane. The effect of all three drugs on testicular steroidogenesis was completely reversible. Thus testicular cells which had been washed after exposure to a greater than 95% inhibitory dose of drug responded in a similar manner to hormone stimulation as cells similarly washed and which had not been exposed to the drug. The sites of the antisteroidogenic effect of epostane, etomidate and cyproterone acetate were established using a method based on the sequential stimulation by the exogenous precursor steroids of the various steps leading to the biosynthesis of testosterone. It was concluded that etomidate acts at the sequence between LH binding and pregnenolone production, epostane acts at 3 beta-hydroxysteroid dehydrogenase and cyproterone acetate inhibits 3 beta-hydroxysteroid dehydrogenase and C17,20-lyase.