The authors studied 15 patients at risk for central adrenocortical insufficiency to evaluate the role of naloxone in establishing the integrity of the hypothalamic-pituitary-adrenal axis. Each patient was admitted to the General Clinical Research Center for 2 days. Naloxone, 125 μg/kg body weight, was administered intravenously, and plasma adrenocorticotropic hormone (ACTH) and cortisol concentrations were measured at -15, 0, 30, 45, 60, 90, and 120 minutes. Metyrapone, 30 mg/kg body weight, was administered orally at 11 PM on the second day of hospitalization. Plasma ACTH, cortisol, and 11-deoxycortisol concentrations were measured at 8 AM pre- and postmetyrapone. The results of the metyrapone test were used to distinguish patients who had central adrenal insufficiency from those who were normal. In 11 patients who had a normal metyrapone test, the plasma ACTH level increased from 6 ± 1 pmol/L at baseline to 11 ± 2 pmol/L 30 minutes after naloxone administration. The plasma cortisol increased from 191 ± 21 nmol/L at baseline to 379 ± 47 nmol/L 45 minutes after naloxone administration. In four patients with central adrenal insufficiency, the plasma ACTH and cortisol concentrations did not increase after naloxone administration. Reliance solely on the individual ACTH and cortisol responses to naloxone would have permitted a correct decision regarding glucocorticoid replacement therapy in 14 (93%) of 15 patients. Naloxone stimulation testing may have a role in the clinical evaluation of patients with suspected central adrenocortical insufficiency.
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