Opioid Modulation of Normal and Pathological Human Chromaffin Tissue
To evaluate whether opioid receptor blockade might modulate sympathetic-adrenal activity, we studied the effects of placebo or naloxone administration on plasma cate-cholamine (CA) levels in a group of 13 normal subjects and 15 hypertensive patients suspected to have a pheochromocytoma. Diagnostic evaluation confirmed the presence of pheochromo-cytoma in 9 patients. Among these, 4 had a unilateral epinephrine (E)-secreting tumor, 3 had bilateral E-secreting tumors due t o multiple endocrine adenomatosis type Ha, and 2 had a unilateral norepinephrine (NE)-secreting tumor. In each subject studied, CA secretion was evaluated by calculating the area (0–30 min) under the plasma hormone curves after placebo or naloxone administratibn. In normal subjects naloxone caused a significant increase (P < 0.005) of E secretion, whereas NE did not change. Similarly, in the group of hypertensive patients, E secretion increased after naloxone (P < 0.01). In pheochromo-cytoma patients naloxone caused a significant increase in E (P < 0.05) and NE (P < 0.01) secretion from E-producing tumors but no increase in the patients with NE-secreting pheochromo-cytomas. The study suggests that CA secretion from normal and pathological chromaffin tissue is modulated by endogenous opioids; this modulation seems particularly evident in patients with E-secreting pheochromocytoma.