Abstract In 25 patients with essential hypertension and 9 control subjects we have studied the effects of central hypervolemia during water immersion on both renin-angiotensin-aldosterone system and renal function (diuresis volume and urine excretion of Na, k and osmoles). Reduction of blood pressure, plasma renin activity and aldosterone was found to be similar in both groups; renal excretion of water, Na, K and osmoles was significantly higher in the hypertensive group compared to the controls. These urinary features may be related to a reduced proximal tubular reabsorption by cardiorenal reflex due to cardiopulmonary volume receptors stimulation without any change of GFR measured as the creatinine clearance. The urinary pattern, observed during water immersion in hypertensive group without any change of plasma sodium, osmolality or protein concentration, was comparable to "exaggerated natriuresis"; this may suggest that also "exaggerated natriuresis" is due either to renal vasodilatation or to renal tubular sympathetic activity reduction secondary to a cardiorenal reflex by cardiopulmonary volume expansion.
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