Quantitative aspects of autoregulation in the canine kidney

Autoregulatory changes in series connected vascular resistances were studied in the normal canine kidney. Two sets of observations were made: a) ureter pressure was increased by ureteral obstruction and b) arterial pressure was decreased by aortic clamping. It was assumed that in both experimental panels the decrement in intrarenal resistance is solely due to dilatation of the preglomerular vessels. Proximal tubular pressure is thought to equal deep venous (wedged) pressure under free flow and ureteral pressure under stop flow conditions. Calculation of the glomerular filtration coefficient yielded the same value in both sets of observations: k similar to 2 ml/min/100 g per 1 mm Hg effective filtration pressure. Glomerular capillary pressure rises steeply and roughly parallels arterial pressue below the autoregulatory range (about 40-80 mm Hg), whereas in the autoregulatory range (about 90-150 mm Hg) its value is stabilized at 74 plus or minus 1 (S.E.)mm Hg. Afferent resistance is negligible in the hypotensive range and increases progressively in the normotensive range. Changes in efferent and venular resistance are insignificant in the whole pressure range considered, i.e. 40 to 150 mm Hg.