Effect of the benzodiazepines diazepam, des-N-methyldiazepam and midazolam on corticosteroid biosynthesis in bovine adrenocortical cells in vitro; location of site of action.

Diazepam and midazolam inhibited cortisol and aldosterone synthesis in bovine adrenal cells in vitro. The biologically active metabolite des-N-methyldiazepam did not. Midazolam was a more potent inhibitor (IC50: 6 micrograms/ml) than diazepam (IC50: 13 micrograms/ml) in ACTH-stimulated cells. Both compounds inhibited steroidogenesis at several points in the biosynthetic chain; the greatest effects were on 17 alpha hydroxylation and 21 hydroxylation. Diazepam had a relatively greater effect on 17 alpha hydroxylation; midazolam on 21 hydroxylation. Both were less potent inhibitors of 11 beta hydroxylation and had little apparent effect on side chain cleavage. Thus microsomal hydroxylation is more vulnerable to benzodiazepines than mitochondrial hydroxylation. It is suggested that the drugs act by competing with steroid mixed function oxidases for cytochrome P-450. The plasma concentrations required for these effects are high in relation to therapeutic levels but may be achieved, for example, during acute infusions or when they are used in combination with imidazole drugs such as cimetidine.

In vivo and in vitro studies of the site of inhibitory action of omeprazole on adrenocortical steroidogenesis.

The site of omeprazole inhibition of adrenal steroidogenesis has been sought in vivo by analyzing the patterns of urinary steroid metabolite excretion after 6 days of treatment with placebo/omeprazole. Excretion rates of androsterone, aetiocholanolone, dehydroepiandrosterone, 11 beta hydroxyandrosterone, tetrahydrocortisone, tetrahydrocortisol and alpha cortolone were reduced, indicating a block at an early step in steroidogenesis, possibly cholesterol side-chain cleavage. In vitro studies have confirmed this finding by measuring conversion of added precursors to cortisol in isolated bovine adrenocortical cells. Cortisol synthesis from added 20 alpha hydroxycholesterol was inhibited by 83% in the presence of 100 micrograms omeprazole/ml. Conversion from pregnenolone and progesterone and their 17 alpha hydroxylated derivatives was inhibited by 20-40% whereas cortisol production from added 11 deoxycortisol was not affected. These data suggest that omeprazole primarily inhibits cholesterol cleavage and does not inhibit 3 beta hydroxysteroid dehydrogenase, 17 alpha hydroxylase or 11 beta hydroxylation; 21 hydroxylase activity may be marginally attenuated.