Acute effects of bromocriptine, cyproheptadine, and valproic acid on plasma adrenocorticotropin secretion in Nelson's syndrome.

Previous studies have found that bromocriptine, cyproheptadine, and valproic acid can reduce ACTH secretion in Nelson's syndrome, but none of these agents has achieved widespread use due to their failure to normalize ACTH in most patients. The current study was undertaken to determine whether these three agents, which act through different mechanisms, decrease plasma ACTH synergistically when administered together. Six adult female patients (mean age, 41 yr) with Nelson's syndrome were studied. ACTH was measured every 20 min for 8 h, 2 h before and 6 h after each of the following six treatments: placebo, bromocriptine (2.5 mg), cyproheptadine (8 mg), valproic acid (1 g), cyproheptadine plus valproic acid, and the combination of all three drugs. The sequence of treatments was determined randomly, and there was an interval of at least 2 days between each treatment. The hourly ACTH values were averaged, and the percent maximal suppression of plasma ACTH, relative to the baseline values before drug administration, was compared among the six treatments. Basal plasma ACTH levels in the six patients ranged from 40-3324 pmol/L (normal range, 1-8). The percent maximal suppression of ACTH after administration of placebo (6 +/- 11%), cyproheptadine (17 +/- 15%), valproic acid (37 +/- 10%) or the combination of cyproheptadine and valproic acid (19 +/- 14%) did not achieve statistical significance. Bromocriptine, on the other hand, caused a significant decrease in plasma ACTH (52 +/- 8%; P < 0.05), as did the combination of bromocriptine, cyproheptadine, and valproic acid (58 +/- 12%; P < 0.05). However, the combined effect of the three drugs did not significantly exceed the effect of bromocriptine alone. We conclude that at the doses studied, bromocriptine had the greatest acute effect in suppressing ACTH secretion in Nelson's syndrome, and that combined administration with valproic acid and cyproheptadine did not further increase this acute ACTH-suppressive effect.