Renal blood flow distribution at varying perfusion pressure in the alloperfused dog kidney

Tissue blood flow (TBF), its percent distribution and glomerular blood flow (GBF) were measured using labelled microspheres 15 micrometer in diameter (M) and chicken red blood cells (CRBC) at perfusion pressures (PP) of 17.3, 12.8 and 8.0 kPa (130, 95 and 60 mm Hg) in isolated alloperfused dog kidneys. Renal blood flow (RBF) was never interrupted during the isolation. Experiments with M showed a marked inequality of the tissue blood flow in different parts of the renal cortex at a constant PP of 17.3 kPa. TBF was highest in the outermost quarter and lowest in the juxtamedullary one. Using CRBC, a homogeneous TBF was observed in the outer 3/4 of the renal cortex with a lower flow in the innermost quarter. With M, a typical percent "redistribution" of TBF and GBF into the inner cortical regions was indicated during PP reduction. With CRBC, this phenomenon was observed only at PP below the range of RBF autoregulation (8.0 kPa) and was much less conspicuous than with M. The smaller size and higher elasticity of CRBC as compared with M, may result in a more realistic reflection of cortical blood flow distribution. The GBF of outermost superficial glomeruli decreases, even with CRBC, with each PP reduction, the difference exhibiting only a 5% significance level. The lower limit of BF autoregulation in these glomeruli seems to be somewhat higher than that of total RBF autoregulation.