Renal clearance of magnesium in sheep given citric acid and(or) potassium chloride.

Two experiments were conducted. The first tested the hypothesis that KC1 or citric acid or both increase plasma clearance of Mg by lowering tubular reabsorption of Mg in the kidney. Plasma and urinary responses in mature ewes to intraruminal KC1, citric acid, KC1 + citric acid and a water control were evaluated in a 4 • 4 Latin square design. An IV injection of Mg (300 mg) at time 0 was used to promote interactions between circulating treatments and plasma Mg, thereby providing a magnification of changes in the tubular reabsorption mechanism. Plasma and urine analysis revealed increased (P<.05) plasma Mg clearances (in relation to control values) due to citric acid and KC1 + citric acid. Increases due to KC1 were noted; however, results were variable. Glomerular filtration rates (creatinine clearances) did not differ (P>.05) between treatments. Only the KC1 treatment tended to cause an increased filtered load of plasma Mg; citric acid and KC1 + citric acid tended to cause reductions in the net tubular reabsorption of Mg. Exp. 2 was designed to test the same "renal antagonists" when plasma Mg was decreased to levels below "normal" (< 1.7 mg/100 ml). Four mature ewes fed a Mg-deficient diet were given the same treatments as in Exp. 1 without an IV injection of Mg. Treatment responses were evaluated through a paired comparison with the previous day, when ewes were not treated. Increases in urinary Mg above control values were induced by KC1 and KC1 + citric acid; however, the magnitude of responses varied. Urinary P and