Role of intrarenal venous pressure in the regulation of renal vascular resistance.

P REPORTS have accounted for autoregulation of renal blood flow on the basis of increases in extravascular pressure" which act as compressing forces on the renal vascular bed. Renal tissue pressures ranging between 2 and 120 mm. Hg have been found to approximate closely the pressures in deep renal veins of a caliber exceeding 0.73 mm. diameter. As a result of these investigations, the concept has been developed that the major driving force for blood flow through the mass of kidney tissue is the difference in pressure between the renal artery and the deep intrarenal veins, which includes virtually all of the renal substance. Another important component of resistance is the contribution of Bowman capsular extravascular pressure to autoregulation by virtue of its additive effect to the generalized renal interstitial pressure. It has been proposed that the net sum of these extravascular forces not only serves to maintain the renal blood flow within narrow but variable limits but, by means of a local feedback, accounts for the regulation of the glomerular filtration rate. The mechanism of autoregulation is accounted for primarily on the basis of rising intrarenal venous pressures, the "prevenous" resistance being relatively constant through the autoregulatory range. Earlier workers, including Winton,among others,' ° have rejected or discounted the tissue-pressure theory of autoregulation, and a recent report by Waugh has attempted to invalidate this explanation of autoregulation on the basis of recorded tissue pressures and intrarenal venous pressures that purport