Relationship between proximal sodium reabsorption and excretion of calcium, magnesium and phosphate

Abstract

Relationship between proximal sodium reabsorption and excretion of calcium, magnesium and phosphate. The relationship between sodium reabsorption by the proximal tubule, measured by micropuncture techniques, and the urinary excretion of calcium, magnesium, and phosphate was determined following a number of experimental maneuvers known to increase sodium excretion. Following intravenous infusion of saline or Ringer's solution and the renal arterial infusions of acetylcholine and prostaglandin E1, proximal sodium reabsorption was significantly decreased while the fractional clearances of Na, Ca, Mg and PO4 were significantly increased. Following the intravenous infusion of hyperoncotic albumin and the renal arterial infusion of parathyroid hormone, proximal sodium reabsorption was significantly decreased and the fractional clearances of Na and PO4 were significantly increased. The fractional clearances of Ca and Mg were not increased following these infusions. Following the renal arterial infusion of bradykinin and prostaglandin E2, there was no significant change in proximal sodium reabsorption or in the fractional clearance of PO4 while the fractional clearances of Na, Ca and Mg were significantly increased. It was concluded that changes in the fractional clearance of PO4 are related to decreases in sodium reabsorption by the proximal tubule. Changes in the fractional clearances of Ca and Mg were not consistently associated with changes in proximal sodium reabsorption, suggesting that the excretion of these ions is primarily controlled by nephron segments distal to the proximal tubule