Decreased calcium and magnesium urinary excretion during prostaglandin synthesis inhibition in the rat.

The effect of endogenous renal prostaglandins on calcium and magnesium reabsorption was investigated. Renal tubular handling of calcium and magnesium was studied by clearance methods in anesthetized Sprague-Dawley and Brattleboro rats, either intact or thyroparathyroidectomized (ATPTX), before and during prostaglandin synthesis inhibition by meclofenamate, indomethacin, or piroxicam infusion. These three inhibitors had similar effects on calcium and magnesium excretion: A significant decrease in absolute and fractional excretions of both cations was observed in intact Sprague-Dawley rats, and in ATPTX rats of both strains, but not in intact Brattleboro rats. These results suggest an inhibitory effect of prostaglandins on vasopressin-, glucagon-, but not PTH-mediated calcium and magnesium reabsorption. This effect is likely to occur in the thick ascending limb of Henle, which is both a target site for these polypeptidic hormones, and a segment where the bulk of calcium and magnesium is reabsorbed.