Renal blood flow varies during normal activity in conscious unrestrained rats

The extent to which renal blood flow (RBF) varied during normal daily activity and its dependence on renal nerve activity were studied in unrestrained rats. RBF (measured with a pulsed Doppler flow probe) and behavior pattern (observed with a video camera) were recorded during both phases of the light-dark cycle (n = 11). RBF was highest (100%) when the rat was fully relaxed and apparently asleep (9% time) but was significantly lower (P less than 0.01) during the remainder of the time. When quiescent but not fully relaxed, RBF was 89.7 +/- 0.3% of the maximum; when alert and completely still, it was 74.1 +/- 0.8%; and when grooming, it was 63.7 +/- 0.9%. Mean daily RBF was 80% of maximum flow. During saline infusion into cuffs around the renal arteries, RBF was reduced to 38.4 +/- 0.7% of maximum flow by gentle handling. When the infusion was changed to Xylocaine (5%), which blocked transmission in the renal nerve, similar treatment reduced RBF to 80.2 +/- 0.7% with ipsilateral and to 94.7 +/- 0.7% with bilateral infusions. We conclude that RBF varies considerably in unrestrained animals under normal conditions and that the variations largely result from changes in renal nerve activity.