Acidosis and hypercalciuria: renal mechanisms affecting calcium, magnesium and sodium excretion in the sheep

Abstract

1. Observations were made on the excretion of calcium and magnesium by the sheep's kidney following manipulation of the acid-base status.2. Intravascular administration of a synthetic solution resembling saliva abolished the naturally occurring acidosis in sheep during feeding, and it also prevented the normal onset of post-prandial hypercalciuria and hypermagnesiuria.3. Non-respiratory acidosis (induced by infusion of hydrochloric acid) and respiratory acidosis arising from inhalation of 6% (v/v) CO(2) in air both caused an acute increase in calcium excretion.4. Measurement of filtered loads showed that feeding exerted an effect on the functional characteristics of the sheep's kidney. The renal clearances of calcium and magnesium increased, whereas sodium clearance decreased.5. Experimental conditions were arranged so that variations in acid-base status could be imposed at a time when the filtered load of calcium was declining.6. With hydrochloric acid-acidosis the renal excretion of calcium increased, despite a steady fall in the filtered load. With sodium bicarbonate alkalosis, the filtered load and the renal excretion of calcium decreased in unison.7. These variations in calcium excretion were not accompanied by corresponding changes in the excretion of sodium.8. It is concluded that the renal tubules in the sheep are sensitive to acid-base status and that they respond to a lowering of the blood pH by decreasing the tubular reabsorption of filtered calcium.