COMPARISON OF DIRECT WITH INDIRECT RENAL BLOOD FLOW, EXTRACTION OF INULIN AND DIODRAST, BEFORE AND DURING ACUTE RENAL NERVE STIMULATION

Abstract

Simultaneous detns. of extraction and excretion of inulin (IN) and diodrast (D), and unilateral renal venous blood flow (BF) measurements (rotameter) were made in anesthetized dogs. During control periods the directly measured and calculated (Fick) BF values agreed closely. The renal nerves to the ipsilateral kidney were stimulated with low frequency AC, and with the strength of stimulus used the following avg. decreases were observed: direct renal BF, 53%; E%IN (and filtration fraction) 38%; E%D, 17%; urine flow, 81%. Glomerular filtration and tubular secretion continued at a reduced rate although urine flow was greatly diminished. Because of the reduction in urine formation during nerve stimulation, IN and D clearances and calculated renal BF were from 1-70% of their true values and all exceeded the latter during recovery with the return of urine flow. A significant in vitro diffusion of D from red cells to plasma occurred within 2 min. after drawing samples. Using whole blood analyses, corrected E% values were obtained. Without correction for diffusion the E%D would have been 2-26% lower and calculated renal BF 3 to 55% higher than the actual values. Constriction of the afferent arterioles appeared to be the primary effect of renal nerve stimulation. There was little or no accompanying change in blood pressure. Dye injected into the aorta during unilateral nerve stimulation caused intense staining of the unstimulated kidney and a pale but diffuse staining of the stimulated kidney. In the expts. performed there was no evidence to suggest that the stimulation caused a shunting of blood from the outer renal cortex to the juxtamedullary areas.