Increased calcium excretion after saline administration to hypertensive subjects.

Abstract

Abstract The renal excretion of sodium and calcium was examined in hypertensive and normotensive subjects following saline infusion and oral water loading. In addition to an exaggerated increase in sodium clearance in the hypertensive subjects, calcium clearances were also significantly higher in these subjects than in those whose blood pressure was normal. After infusion of saline the relationship between sodium and calcium clearances remained constant despite widely varying rates of sodium clearance. Regression lines relating calcium clearance to sodium clearance were the same in the 2 groups. Urine volume and free water clearance were higher in the hypertensive subjects, indicating diminished sodium reabsorption in the proximal tubule. Free water clearance per unit volume was diminished in the hypertensive subjects and the minimum urinary sodium concentration was higher, findings in keeping with previous reports indicating defective sodium reabsorption in Henle's loop following saline infusion in hypertensive subjects. These findings establish the interrelationship between sodium and calcium excretion in another clinical and experimental situation. The parallel increases in sodium and calcium clearances provide evidence in human beings that the reabsorption of calcium and sodium is linked in the proximal tubule and in the loop of Henle, a relationship established in animal experiments. These data also provide further evidence of decreased sodium reabsorption in the proximal tubule and loop of Henle after saline administration to hypertensive subjects.