Heterogeneity of intracortical peritubular plasma flow in the rat kidney

The 86 Rb-accumulation technique was adapted to the study of intracortical peritubule plasma flow patterns in the rat kidney. A rapid intravenous bolus of 86Rb (50 micronCi) was given to anesthetized nondiuretic rats. One kidney pedicle was tied at 6 s, the other at 12 s. In group I (1o rats) [3H]PAH clearance was measured prior to the 86Rb bolus. In group II (six rats) 86Rb and [3H]PAH (100 micronCi) were given together. The kidneys were snap-frozen, then sliced at -6 degrees C. There were no differences in renal plasma flow (RPF) as measured by either tracer in either group, no differences in the intracortical distribution of [3H]PAH and 86Rb, and no changes in the 86Rb distribution between 6 and 12 s. Tissue plasma flow (TPF) as measured by 86Rb in ml/min per g was 3.88 +/- 0.22 (SE) (142% of RPF/g kidney wt) for cortex 1 (outermost), 3.90 +/- 0.21 for cortex 2, 3.26 +/- 0.14 for cortex 3 (P less than 0.025), 2.17 for cortex 4 (P less than 0.001), 1.34 for cortex-medulla junction (P less than 0.001), and 0.88 +/- 0.07 for outer stripe (P less than 0.001). Peritubular capillary plasma flow, derived as TPF minus GRF/g in each slice, fell progressively from cortex 1 to outer stripe. This is thought to represent lower perfusion rate of "medullary rays."