A simple in vitro approach to the estimation of the biopotency of drugs affecting adrenal steroidogenesis.

Dispersed guinea-pig adrenal cells can be maximally stimulated to secrete cortisol by adrenocorticotrophin (ACTH greater than 50 ng/l). Further, this stimulation appears to be specific to ACTH alone, with other naturally occurring chemicals (e.g. steroids, protein hormones) at supra-physiological concentrations being without effect on cortisol production. The effect of drugs of differing structure and therapeutic function (aminogluthethimide, metyrapone, trilostane, 17-ketotrilostane, danazol, epostane, megestrol acetate, stanozolol and etomidate) on ACTH-stimulated (50 ng/l) cortisol production has been tested in this system. All the drugs depressed steroid output in a similar dose-related fashion. The concentration of drug which inhibited cortisol output by 50% was (mumol/l, mean +/- SEM): etomidate 0.097 +/- 0.002: epostane 0.44 +/- 0.02: 17-ketotrilostane 0.55 +/- 0.04: trilostane 1.3 +/- 0.1: metyrapone 3.5 +/- 0.6: megestrol acetate, 11 +/- 2: danazol 22 +/- 2: aminogluthethimide 41 +/- 5: stanozolol 50 +/- 4. Thus, etomidate, an anaesthetic, is more potent than the established anti-steroidogenic drugs metyrapone, aminogluthethimide and trilostane. Further, direct anti-steroidogenic effects have been demonstrated for megestrol acetate and stanozolol for the first time. We conclude that this technique offers a promising new approach to the assessment of biological potency of drugs affecting endocrine tissues.