Effects of volume expansion and parathyroid hormone on total renal blood flow and its intracortical distribution

Clearance and renal blood flow studies were performed during hydropenia, 2.5 and 10 percent steady-state saline expansion, and acute administration of parathyroid hormone (PTH) in chronically thyroparathyroidectomized (TPTX) dogs and during hydropenia and 10 percent expansion in intact dogs. Renal cortical blood flow distribution was measured with radioactive microspheres. In TPTX dogs, 2.5 percent expansion increased sodium excretion but did not alter total or intracortical blood flow. With 10 percent expansion, sodium excretion and juxtamedullary (zone 4) blood flow increased in both TPTX and intact dogs. There was no correlation between the changes in sodium excretion and zone 4 fractional blood flow in either group. Although the acute administration of PTH to TPTX dogs did not alter total or intracortical blood flow, control period hemodynamic data revealed an inner shift of flow in TPTX as compared to intact dogs. These results indicate that (1) massive (10 percent), but not mild (2.5 percent), volume expansion produces an inner shift of cortical blood flow; (2) this shift does not correlate with sodium excretion, nor is it influenced by thyroparathyroidectomy; and (3) PTH does not acutely alter renal blood flow distribution, but its chronic absence is associated with a shift of flow to the inner cortex.