The antiglucocorticoid and antiprogestin steroid RU 486 suppresses the adrenocorticotropin response to ovine corticotropin releasing hormone in man

Abstract

The glucocorticoid and progesterone antagonist RU 486 normalizes the clinical and biochemical features of hypercortisolism in patients with nonpituitary Cushing's syndrome, presumably by antagonizing the action(s) of cortisol. Since RU 486 has progesterone agonist activity in addition to its progesterone antagonist action, the possibility that it might have some glucocorticoid agonist action did not seem unreasonable. To test this hypothesis we examined the effects of RU 486 on pituitary ACTH secretion in 10 patients with primary adrenal insufficiency in whom glucocorticoid replacement was withheld for 36 h. Each patient received, in randomized sequence 3-7 days apart, an oral dose of placebo, RU 486 (20 mg/kg), cortisol (0.1 mg/kg), or a combination of RU 486 and cortisol at 1800 h. Two hours later, an iv bolus dose of ovine CRH (1 microgram/kg) was administered, and plasma ACTH levels were measured serially for 3 h. RU 486 suppressed ovine CRH-stimulated ACTH secretion, albeit less than cortisol. Its glucocorticoid agonist effect was calculated to be approximately 1/250th that of cortisol on a weight basis. Additionally, RU 486 partially antagonized cortisol-induced suppression of ACTH secretion. These findings suggest that RU 486 is a partial glucocorticoid agonist and offer some insight as to its action in patients with Cushing's syndrome. Whether this degree of glucocorticoid agonist activity is adequate to support life, however, is not known.

PIP: The purpose of this study was to assess the glucocorticoid agonist activity of the antiprogestin steroid RU-486 by examining its ability to exert a glucocorticoid-like negative feedback effect on pituitary adrenocorticotropic hormone secretion. 10 patients with nonpituitary Cushing's syndrome, from whom cortisol therapy had been withheld for 36 hours, were given an oral dose of either a placebo, cortisol, or 20mg/kg of RU-480. 2 hours later, they were given an intravenous injection of lug/Kg of ovine corticotropin-releasing hormone. Blood samples were taken 15 minutes before the injection, at the time of the injection, and 15, 30, 60, 90, 120, and 180 minutes afterwards to measure adrenocorticotropic hormone and cortisol levels. Blood samples from the patients who received the RU-486 showed that RU-486 had suppressed the ovine corticotropin-releasing hormone-stimulated secretion of adrenocorticotropic hormone. However, the RU-486-induced suppression of the secretion of adrenocorticotropic hormone was only 80% that of the suppression induced by .1 mg/kg of cortisol, i.e., RU-486 had only 1/250 the glucocorticoid agonist effect of cortisol. RU-486, therefore, is a partial glucocorticoid agonist, but the effect is not of sufficient magnitude to prevent adrenal insufficiency in patients with nonpituitary Cushing's syndrome.