Distribution of blood flow in the dog kidney IV. Reversed net inward postglomerular capillary flow in the cortex after blocking interlobular arteries by 50 μm microspheres

Simultaneous measurement of glomerular flow by 15 μm microspheres (Ms) and postglomerular capillary flow by ¹²⁵I‐iodoantipyrine (I‐Ap) suggest that about 10% of total RBF flow inward through the entire cortex in the postglomerular capillaries of the dog kidney. This flow fraction might be variable (Clausen et al. 1978, 1980) and perhaps even reversible. To test this possibility we injected 50 μm Ms into the renal artery in order to obstruct interlobular arteries and produce a selective reduction of outer cortical glomerular blood flow and postglomerular pressure. The 50 μm Ms reduced total RBF by 50%. In the outer cortex, postglomerular flow measured by I‐Ap was significantly less reduced than glomerular flow as measured by 15 μm Ms: Whereas the inward flow fraction from inner cortex to the medulla was maintained, about 5% of RBF now drained from midcortex to outer cortex. This observation support the theory of a variable net postglomerular capillary flow of radial direction in the cortex of the dog kidney.