Distribution of blood flow in the dog kidney. III. Local uptake of 10 mum and 15 mum microspheres during renal vasodilation and constriction.

Recent studies indicate that intrarenal distribution of blood flow measured with microspheres (Ms) during control conditions depends on Ms size. We therefore compared local flow in outer and middle cortex (C1 and C2) and inner cortex plus the medulla (C3M) using 10.5-12.0 and 13.9-15.0 mum Ms (Ms 10 and Ms 15). One pair of Ms 10 and Ms 15 was injected during control and a second pair at 80% increased or 50% decreased total renal vascular conductance (RVC), as induced by infusion of acetylcholine (Ach) and angiotensin II (Ang) or noradrenaline (NA). All zones participated in dilation and constriction, as indicated by both Ms sizes. Ms 15 underestimated C3M flow as compared to Ms 10, by 19% during control or Ang, and by 3% during Ach (P less than 0.02). The C3M flow fractions increased during Ach and decreased during Ang, whereas NA gave greatly variable results, on average no change. Renal Ms extraction averaged 97.0 +/- 3% for Ms 10, 98.6 +/- 2.4% (S.D.) for Ms 15. About 8% of Ms 10 and less than 1% of Ms 15 were located in peritubular capillaries in each cortical zone. Neither total Ms extraction nor zonal extraglomerular Ms fraction changed over the present RVC range. Thus, the Ms 10 to Ms 15 differences as well as the observed redistribution must be due to differences in local entry of Ms into the afferent arterioles. However, steric restriction of Ms at arteriolar inlets did not play a significant role. The measured redistribution of fractional flow could in part be due to skimming of Ms at arteriolar inlets along the interlobular arteries (i.l.a.), depending on the C3M flow fraction, Ms size and i.l.a. diameter. If the observed fractional flow redistributions were solely due to variable Ms skimming, Ms 15 underestimated C3M flow by 53%, Ms 10 by 43%, during Ang as compared to Ach. Although Ms 10 and Ms 15 may correctly indicate the direction of fractional glomerular flow redistribution, at least Ms 15 overestimates this phenomenon quantitatively.