The effect of ketoconazole on steroidogenesis. II. Adrenocortical enzyme activity in vitro.

The activity of five adrenocortical steroidogenic enzymes, 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD), 17-hydroxylase (17-OHase) 17,20 desmolase (17,20D), 21-hydroxylase (21-OHase) and 11-hydroxylase (11-OHase), were measured in vitro in purified mitochondria or microsomes from rhesus monkey (Macaca mulata) and human adrenal tissue in the presence and absence of graded concentrations of ketoconazole. Rhesus 3 beta-HSD activity was unaffected by ketoconazole at concentrations up to 5000 microM. However, human adrenal 3 beta-HSD was inhibited by approximately 40% (p less than .01) at concentrations of 500 microM and by 80% at 100 microM. 17-OHase and 17,20D were significantly inhibited in the human at 5 microM (p less than .001) and in the rhesus monkey at 50 microM (p less than .001). A similar inhibitory effect was found on microsomal 21-OHase, with significant inhibition at 5 microM ketoconazole in the human and rhesus monkey (p less than 0.001). Mitochondrial 11-OHase was also significantly inhibited by ketoconazole in both the human (p less than .005) and rhesus (p less than .001) at 2.0 microM. These results represent documentation of the specific adrenal steroidogenic steps affected by ketoconazole and confirm the observations that this imidazole derivative is a powerful inhibitor of enzymes in the glucocorticoid pathway.