Effects of hypercalcemia on calcium and phosphate ultrafilterability and tubular reabsorption in the rat
Harris, C.A.; Sutton, R.A.; Dirks, J.H.
American Journal of Physiology 233(3): F201-F206
1977
ISSN/ISBN: 0002-9513 PMID: 910914 Document Number: 123931
Micropuncture and clearance studies were carried out on Munich-Wistar rats in order to determine the effects of hypercalcemia on glomerular ultrafilterability and tubular reabsorption. Direct punctures of surface glomeruli showed that Ca infusion decreased the percentage of ultrafilterable Ca from 60-47% and decreased the percentage of ultrafilterable phophate from 98-78%. The Ca infusion increased total plasma Ca from 5.7 .+-. 0.1-9.2 .+-. 0.3 meq/l and plasma phosphate from 6.6-8.0 mg/100 ml. The glomerular ultrafilterability of both Ca and phosphate were inversely correlated with plasma Ca, consistent with the formation of nonultrafilterable Ca-phosphate complexes in the plasma. Addition of Ca to rat plasma in vitro increased plasma Ca from 5.3-11.5 meq/l and decreased ultrafilterability of Ca through artificial membranes from 55-42%. Ultrafilterability of phosphate decreased from 96-42%. Hypercalcemia decreased proximal reabsorption by an undefined mechanism, the TF/P or fractional phosphate excretion was observed.