AUGMENTATION OF THE RENAL TUBULAR DOPAMINERGIC ACTIVITY BY ORAL CALCIUM SUPPLEMENTATION IN PATIENTS WITH ESSENTIAL-HYPERTENSION

We studied the effect of oral calcium supplementation on renal tubular dopaminergic activity in patients with mild to moderate essential hyp ertension. Fifteen patients aged 45 to 68 years (nine men and six wome n, mean age 59 +/- 7 [SD]) participated in the study. We orally admini stered calcium (1.0 g per day for 1 week) during hospitalization. The change in 24-h blood pressure (BP), measured by ambulatory BP monitori ng, and extretions of electrolytes and catecholamines were investigate d before and after 1 week of oral calcium supplementation. The mean va lues of 24-h systolic and diastolic BP showed no significant changes b y calcium loading. Daily urinary excretion of free dopamine, sodium cl earance (C(Na)), fractional excretion of sodium (FE(Na)), and urinary volume were significantly increased by oral calcium supplementation. U rinary excretions of epinephrine and norepinephrine and creatinine cle arance showed no significant changes by oral calcium treatment. C(Na) and FE(Na) showed significant correlations with urinary excretion of f ree dopamine. These results suggest that oral calcium supplementation induces natriuresis partly through augmentation of renal tubular dopam inergic activity.