Pre- and postglomerular resistance changes in the isolated perfused kidney

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Abstract
The objective of the present study was to evaluate the relative roles of pre- and postglomerular vascular resistance changes in the autoregulation phenomenon. Experiments were performed on isolated dog kidneys perfused during ureteral occlusion. Ureteral pressures were assumed to approximate Bowman capsule extravascular pressure. As renal artery pressure was progressively elevated through the autoregulatory range, ureteral, intrarenal venous, and tissue pressures were measured; glomerular and peritubular capillary pressures were estimated, and pre- and postglomerular resistances were calculated. Results indicate that autoregulation of renal blood flow is brought about by the combined effects of increased tissue pressure and Bowman capsule extravascular pressure. Progressive increases in postglomerular resistance are responsible for the rise in ‘over-all’ renal resistance. Data provide evidence for the absence of the ‘myogenic reflex’ as a causal factor in autoregulation. Results are in agreement with previous reports of Winton and Gómez regarding glomerular pressure estimations and renal segmental resistance calculations.