Abnormal tubular handling of sodium and water induced by atrial natriuretic peptide in essential hypertension

Atrial natriuretic peptide (ANP) was given as an intravenous bolus injection (2.0 micrograms kg-1) to 12 essential hypertensive patients (EH) and 13 normotensive control subjects (C) in order to study the effect of ANP on renal glomerular and tubular function using the lithium clearance technique. Urinary sodium excretion (EH, + 370% vs. C, + 120%; P less than 0.001) and urine volume (EH, + 137% vs. C, + 62%; P less than 0.01) increased significantly more in EH than in controls after ANP injection. Glomerular filtration rate, renal plasma flow, and plasma concentrations of angiotensin II, aldosterone and arginine vasopressin remained almost unchanged after ANP injection, whereas the filtration fraction increased to the same extent in both groups. Both proximal (EH, - 15% vs. C, - 5%; P less than 0.01) and distal fractional reabsorption (EH, - 12% vs. C, - 5%; P less than 0.01) of sodium decreased more markedly after ANP in EH than in controls. The increase in plasma cGMP and urinary excretion of cGMP was the same in the two groups. Mean blood pressure decreased and heart rate increased to the same extent in both groups. It is concluded that the increase in urinary sodium excretion and urine volume induced by ANP bolus injection is exaggerated in EH due to a more pronounced reduction in the reabsorption of sodium and water in both the proximal and the distal tubule.