Role of serum Ca, parathyroid hormone, and NaCl infusion on renal Ca and Na clearances.

MASSKY, SHAUL G., JACK W. COBURN, LLOYD W. CHAPMAN, AND CHARLES R. KLEEMAN. Role of serltm Ca, parathyroid hormone, and NaCl infusion on renal Ca and Na clearances. Am. J. Phvsiol. 214(6): 1403-1409. . 1968.-The effect of changes in serum calcium and parathyroid hormone (PTH) levels was studied in 15 thyroparathyroidectomized (T-PTX) dogs receiving CaClz and/or NaCl infusion in different sequences and rates and, in some, parathyroid extract (PTE). In T-PTX dogs calcium clearance (Co.) was 4-6 times greater than sodium clearance (C,,) with CCn/CNa of 5.10 =t 0.94 (mean & SE). After PTE, Cca fell and Ces/CNa returned to normal. During CaClz infusion both calcium and sodium excretion increased, but Cca was disproportionately higher than CNa at all levels of serum calcium. During calcium infusion natriuresis occurred despite acute reduction in GFR and filtered sodium. Saline infusion to hypoor normocalcemic T-PTX dogs restored Co, /C Na to normal. During hypercalcemia, the high C&,/C,, was not influenced by saline infusion or PTE administration. The results indicate that: 1) the normal interdependence between Cclt and CNa is altered by PTH, 2) renal sodium reabsorption is depressed during calcium infusion, and 3) during hypercalcemia, either increased filtered calcium or high extracellular or tubular fluid calcium concentration may primarily alter the relation between Ccn and C Nn-