COMPARISON OF RENAL CLEARANCES WITH DIRECT RENAL BLOOD FLOW UNDER CONTROL CONDITIONS AND FOLLOWING RENAL ISCHEMIA

Abstract

Renal blood flow calculated from the renal plasma clearance of p-aminohippuric acid (PAH) and hematocrit volume avgs. 91% of whole renal blood flow measured simultaneously by a direct method in anesthetized dogs. This confirms the postulate that PAH clearance at low plasma concns. is a reasonably accurate measure of renal plasma flow under control conditions. Following a 20 min. period of complete renal ischemia, there occurs a prolonged period of increased renal vascular resistance, evidenced by a reduction of vol. of direct blood flow. It is suggested that the increased renal vascular resistance is largely the result of arteriolar vaso-constriction. Renal tubular impairment results from the anoxemia created by renal arterial occlusion, as evidenced by reduction in the plasma extraction ratio of PAH and by decrease in the concentration ratio (U/P) of creatinine at reduced urine flows. These changes are reflected in a greater percentile reduction in the clearances of PAH and creatinine than simultaneous direct blood flow, resulting in discrepancies in the renal clearances of these substances.