Hyposthenuria in hypercalcemia. A possible role of intrarenal blood-flow (IRBF) redistribution.

Abstract

The intrarenal blood flow (IRBF) distribution has been studied in dogs during acute and chronic calcium intoxication, using clearance technique,85Kr disappearance curves, autoradiograms, and silicone rubber injections. The purpose of this study was to determine whether a modification of the IRBF could be responsible for the decrease of the cortico-medullary osmotic gradient and the hyposthenuria generally observed in these conditions. Acute hypercalcemia was produced in 12 dogs by infusing a solution of CaCl2 into the left renal artery. 20 min after starting infusion (PCa in renal vein = 7.34 mEq/l), the urinary osmolarity and the TcH2O were slightly decreased on the experimental side (P<0.05). C.PAH was also depressed (P<0.005), while E.PAH remained constant. The85Kr curves and the autoradiograms reflected a redistribution of IRBF toward the deeper region of the kidney. In 10 dogs chronically intoxicated with vitamin D, (PCa=6.68 mEq/l) the U.osm and TcH2O were markedly depressed (P<0.001). Renal tissue analysis showed a significant fall of the cortico-medullary osmotic gradient of Na. In parallel, a decrease in C.PAH was observed.85Kr curves demonstrated a significant redistribution of IRBF with a decrease of the percent of initial radioactivity in the cortex. Autoradiograms and silicone rubber vascular casts also demonstrated a vasodilatation of the vasa recta of the medulla. These data therefore support the conclusion that a redistribution of IRBF contributes to the hyposthenuria observed during hypercalcemia.