Essential hypertension with low conjugated catecholamines imitates pheochromocytoma.

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Abstract
The correlation between the degree of conjugation of plasma norepinephrine (NE) and epinephrine (E), and the clinical features of sympathetic hyperactivity, was studied in 38 essential hypertensive patients. The patients were separated into 2 groups: 15 with subnormal plasma conjugated NE + E, i.e., < 0.23 ng/ml (group 1), and 23 patients above this limit (group 2). Patients clinically suspected of pheochromocytoma represented 93% of the patients in group 1, but only 21% in group 2. Group 1 patients, compared to those of group 2, had: higher baseline plasma free NE + E (P < 0.02); an increase in plasma-free NE + E in response to stressful sampling (P < 0.05) and a more pronounced response (P < 0.05) to glucagon administration; higher free NE + E and DA [dopamine] in the regional samples received during catheterization while conjugated NE and/or E were usually absent; and a higher spread between maximum and minimum blood pressure and a higher maximum pulse rate recorded, as well as the index of sympathotonia. All patients combined had the maximum pulse rate correlated negatively (P < 0.005) with conjugated NE + E but positively (P < 0.005) with free NE + E. The clinical and biochemical similarity to pheochromocytoma was particularly striking in some group 1 patients who had a selective defect in E conjugation. The association of subnormal conjugated plasma NE and/or E with moderately elevated plasma NE + E, and a more frequent pseudopheochromocytoma presentation, may result from inadequate conjugation and hence inactivation of NE and/or E. Excessive free catecholamines would account for the clinical symptoms and for the fact that the patients are well controlled by treatment with .beta.-adrenergic blocking agents, alone or in combination with .alpha.-blockers. Awareness of the existence of this variety of essential hypertension can obviate unnecessary surgery for wrongly suspected pheochromocytoma.