Microcirculation of the renal papilla of rats under control conditions and after temporary ischemia.

Blood flow velocities were measured and, with the help of vessel diameters, volume flow rates were calculated in the ascending and descending vasa recta of the renal papilla of young rats using microkymography. Measurements were done under control conditions, and one or three days after temporary ischemia of the kidney (one hr of renal artery occlusion). To test whether the osmolality of the final urine which surrounds the papilla influences the papillary microcirculation, the papillary surface was rinsed with 300 or 1500 mOsm solutions. However, the rinse fluid osmolality had no effect on blood flow. Flow velocity in descending vasa recta(hypertonic rinse fluid) averaged 0.60 +/- 0.04 SEM mm/sec under control conditions, 0.68 +/- 0.08 mm/sec one day after temporary ischemia, and 0.73 +/- 0.04 mm/sec three days after temporary ischemia. The corresponding blood flow rates are 9.3 +/- 1.0, 8.3 +/- 1.2, and 10.5 +/- 1.5 nl/min; these values are not significantly different from each other. Flow rate in the ascending vasa recta was 6.4 +/- 0.6 nl/min under control conditions and 9.3 +/- 1.2 nl/min one day postischemia. The significance increase in ascending vasa recta blood flow after ischemia was probably due to an increase in the permeability of the papillary epithelium. An exact quantitative comparison between blood inflow and outflow from the papilla is not possible at present, because it is not yet clear to what extent the number of ascending vasa recta outnumber the descending vasa recta.