Lysine vasopressin stimulation of cortisol secretion in patients with adrenocorticotropin-independent macronodular adrenal hyperplasia.

We present two patients with Cushing's syndrome due to ACTH-independent macronodular adrenal hyperplasia who showed marked plasma cortisol response to lysine-8-vasopressin (LVP) injection (from 930 and 731 pmol/L to 2177 and 1920 pmol/L, respectively), while plasma ACTH levels remained undetectable. The ACTH independence of cortisol secretion in the two patients was determined from the following endocrinological findings. Plasma cortisol levels were not increased by corticotropin-releasing hormone injections and were not suppressed by high dose (16 mg) dexamethasone administrations. The plasma ACTH levels, measured by two independent sensitive immunoassays, were persistently undetectable even after corticotropin-releasing hormone injection, metyrapone administration, and bilateral adrenalectomy. The particular pathological finding of the two cases, atrophic lesions in nonnodular parts of the adrenal cortexes, also indicated ACTH independence of the macronodular hyperplasia. In vitro examination revealed a direct effect of LVP on cortisol secretion from the adrenal cells of the macronodules. We also examined seven patients with Cushing's syndrome caused by adrenal adenoma and found a statistically significant plasma cortisol response to LVP injection. The direct effect of LVP was also demonstrated in cultured adenoma cells. In conclusion, we discovered a direct adrenal effect of LVP on cortisol secretion in patients with ACTH-independent macronodular hyperplasia and, to a lesser extent, in patients with cortisol-producing adrenal adenoma. The cortisol response to LVP may serve to facilitate their diagnosis and choice of therapy.