Plasma beta-endorphins and catecholamines before and after clonidine in essential hypertension and pheochromocytoma

To investigate the possible release of beta-endorphins (beta EN) 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 beta EN, 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 less than 0.01) decrease in MAP was present in all groups. Plasma NE and E decreased (p less than 0.02 to p less than 0.01) in N, BEH, and SEH, but not in PHEO. DA did not change in any group. Pretreatment beta EN 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 less than 0.01) and in SEH (p less than 0.02). Absolute changes in MAP correlated with those of beta EN 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 beta EN, in N or EH, but a correlation between resting plasma E and resting beta EN concentrations was demonstrated in PHEO. These results support a role of beta EN in the hypotensive action of CLO in EH, but not in N or PHEO.(ABSTRACT TRUNCATED AT 250 WORDS)