Free and Conjugated Plasma and Urinary Dopamine in Human Hypertension*

Abstract

Plasma and urinary free and conjugated dopamine (DA) were determined, with the use of a new method of hydrolysis of conjugated catecholamines, in 29 patients with essential hypertension (EH), 4 with primary aldosteronism (PA), and 3 with phaeochromocytoma (normotensive phase), as well as in 16 control subjects. Plasma free DA is not detectable in most subjects. Mean conjugated plasma DA was found to be significantly elevated in EH, PA, and phaeochromocytoma patients [1.97 ± 0.3, 3.1 ± 0.3, and 3.3 ± 1.2 (SE) ng/ml, respectively, vs. 0.98 ± 0.1 ng/ml in control subjects]. Urinary free DA was lower in EH patients than in PA subjects. Total urinary DA was higher in PA patients than in control and EH subjects. After iv furosemide, there was less increase in the urinary excretion of sodium (P < 0.05) and free DA (P < 0.005) in EH patients than in controls. The elevated urinary free and total DA excretions in PA patients returned toward normal when their adrenal adenomas were removed. The elevated plasma total DA in several forms of hypertension is compatible with the existence of a dopaminergic vasodilator system, which is stimulated in hypertension as a compensatory mechanism. Since urinary free DA correlated with sodium excretion, the low DA excretion in EH suggests an intrinsic defect in a DA-modulated natriuretic mechanism in this condition. In PA patients, this mechanism appears to be activated to counteract the sodium-retaining action of the hyperaldosteronism. It returns to normal when the aldosterone-producing tumor is removed. (J Clin Endocrinol Metab48: 425, 1979)