DISTRIBUTION OF BLOOD-FLOW IN THE DOG KIDNEY .1. SATURATION RATES FOR INERT DIFFUSIBLE TRACERS, IODOANTIPYRINE-I-125 AND TRITIATED-WATER, VERSUS UPTAKE OF MICROSPHERES UNDER CONTROL CONDITIONS

Disparate reports on intrarenal blood flow distribution prompted a direct comparison between microspheres (Ms) and inert diffusible tracers (DT). The “tissue sampling technique” for estimating local flow with DT (Kety) was adapted for the dog kidney, using 125I‐iodoantipyrine (I‐Ap) and tritiated water (THO). Ms (15 μm) were injected 2–3 min prior to 10–15 s DT infusion made during continuous 1 s arterial blood sampling. Tracers were measured in 7 to 20 samples from each of the following zones: Outer, middle and inner cortex (C1, C2, C3), outer and inner halves of outer medulla (OM1, OM2), and inner medulla (IM). I‐Ap and THO gave closely similar flow distributions, and average total renal blood flow (RBF) of 3.90 and 3.78 as compared to 3.94 ml/min g with Ms. Flow in C2 (ml/min g) was similar with all tracers, and in per cent thereof average local flows were: C1 102, C3 70, OM1 34, OM2 12, and IM 2 with DT versus 117, 53, 12, 3, and 0 with Ms. Zonal flow fractions of total RBF obtained with DT were: C1 0.41, C2 0.33, and C3+medulla 0.26 versus 0.51, 0.33 and 0.16 with Ms. Thus, a Ms surplus in C1 relative to DT flow, representing 10% of total RBF, matched a Ms deficit in C3+medulla. This disparity might result from: (1) Failure of Ms to enter deep afferent arterioles in proportion to blood flow, (2) diffusion of DT from deep portions of the interlobular arteries, and/or (3) postglomerular inward flow of blood and DT. © 1979 Scandinavian Physiological Society