Plasma β-Endorphins and Catecholamines Before and After Clonidine in Essential Hypertension and Pheochromocytoma

Abstract

To investigate the possible release of β-endorphins (βEN) from tumors and to investigate their possible involvement in the hypotensive mechanism of clonidine (CLO) in pheochromocytoma (PHEO), as compared with essential hypertension (EH), we studied 12 patients with PHEO, 17 patients with uncomplicated stable EH (SEH), nine patients with borderline EH (BEH), and seven healthy volunteers (N). All subjects were hospitalized and excreted normal amounts of sodium. Mean blood pressure (MAP) and plasma βEN, norepinephrine (NE), epinephrine (E), and dopamine (DA) were measured before and 180 min after an oral dose of 0.3 mg CLO. Following CLO, a significant (p < 0.01) decrease in MAP was present in all groups. Plasma NE and E decreased (p < 0.02 to p < 0.01) in N, BEH, and SEH, but not in PHEO. DA did not change in any group. Pretreatment βEN did not differ significantly between the groups, and following CLO it did not change in N or PHEO, while it increased significantly in BEH (p < 0.01) and in SEH (p < 0.02). Absolute changes in MAP correlated with those of βEN only in the SEH group. Changes in NE or E did not correlate with changes in MAP in either group. Likewise, changes in NE or E were not correlated with those of βEN, in N or EH, but a correlation between resting plasma E and resting βEN concentrations was demonstrated in PHEO. These results support a role of βEN in the hypotensive action of CLO in EH, but not in N or PHEO. They do not demonstrate unequivocally an increase of plasma βEN in PHEO, which could reflect release from tumors or other sources, but they do suggest that in patients with PHEO βEN and E might be released from a common source, possibly the tumor itself.