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This study investigates the release of Neuropeptide Y from eight human pheochromocytomas. Profil immunoreactive Neuropeptide Y (Ir-NPY) levels during the management of surgery were compared with these of norepinephrine (NE) while hemodynamics were monitored. Plasma IrNPY and NE levels increased during tumor manipulation and returned to near normal one hour after operation. However, Ir-NPY levels remained high just after tumor resection while NE levels were significantly decreased. At tumor manipulation and just after tumor resection, plasma Ir-NPY levels were correlated with the systemic vascular resistances (SVR) (r = 0.74; P<0.04 and r = 0.86; P<0.006 respectively). No correlation was found either between plasma Ir-NPY and NE levels or between plasma NE levels and SVR. The release of Ir-NPY from tumor tissue, studied by a superfusion method, exhibited a significant correlation with the plasma Ir-NPY concentrations at the time of corresponding tumor resection (r = 0.95; P<0.007). Chromatographic analysis showed that Ir-NPY in plasma and outflow migrate as human NPY (1-36). These results confirmed that in pheochromocytoma, plasma NPY mainly originates from the tumor and argue for an important role of NPY in pheochromocytoma hypertension as indicated by the correlation between the Ir-NPY levels and the SVR.

The presence of functional receptors for human atrial natriuretic hormone in human pheochromocytomas was recently reported. The present study reports the binding of hANH as measured by Scatchard analysis in 4 human adrenal glands and in 5 human pheochromocytomas. Binding assays using [3H]ANH revealed a single class of high-affinity binding sites for hANH in both tissues. Human pheochromocytomas present a lower number of binding sites than normal human adrenal gland (Bmax of 7.1 +/- 2.1 vs 33.6 +/- 6.9 fmol/mg protein, respectively). However, the decreased number of ANH receptors was not paralleled by modifications of tissular cyclic GMP (cGMP). Moreover, plasma hANH concentrations in 7 patients with pheochromocytomas (20.2 +/- 2.7 pmol/l) were statistically higher than those obtained in 25 normal control humans (8.1 +/- 0.6 pmol/l, p less than 0.001). We also demonstrated the presence of immunoreactive ANH in the tumour itself.