Evaluation of the Cell Separation Hypothesis of Autoregulation of Renal Blood Flow and Filtration Rate

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Abstract
Renal blood flow (RBF) and glomerular filtration rate (GFR) were measured in anesthetized normal and anemic dogs at normal and reduced renal arterial pressures. Reductions in pressure were produced by inflation of a balloon catheter positioned fluoroscopically above the origins of the renal arteries. Sampling of renal venous blood via a catheter inserted under fluoroscopic visualization allowed a calculation of renal blood flow by the Fick equation, utilizing PAH excretion and blood values. Control values of GFR and RBF progressively declined during the course of most experiments. After correction of data to constant control values, it was found that autoregulation of GFR and RBF was present in both normal and anemic animals to approximately the same degree. These findings are in contrast to the reports of Pappenheimer and Kinter, who found a reduction or loss of autoregulation in acutely anemic cats, and in a few anemic dogs. In accord with the findings of Pappenheimer and Kinter, we found a reduction in PAH extraction in the anemic animals. However, we failed to find a correlation between PAH extraction and arterial pressure, which argues against their thesis of cell separation as a cause of autoregulation. In a separate series of experiments it was found that plasma volume expansion by dextran or plasma was usually associated with a reduction in PAH extraction but that there was no apparent correlation between the extent of the expansion of plasma volume and the extent of the reduction in PAH extraction.