Oscillations of tubular pressure, flow, and distal chloride concentration in rats.

Previous experiments have shown oscillations in proximal tubular pressure in halothane-anesthetized rats. Such oscillations should be due to oscillations in flow rate and should cause periodic oscillations in both distal tubular chloride concentration and distal tubular pressure. The purpose of the study was to test these predictions. In halothane-anesthetized Sprague-Dawley rats, distal tubular chloride activity was measured with Cl- -sensitive electrodes, and late proximal flow rate was measured by pulse injection of boluses of solutions containing rhodamine dextran. Bolus velocity was detected by videomicroscopy. The time resolution was 2 s. All four variables oscillated with the same frequency, approximately 35 mHz. The amplitude of the flow and the chloride oscillations were 28 and 10%, respectively, of the mean values. Proximal fluid velocity led proximal pressure by 1.5 +/- 0.4 s, whereas distal chloride activity lagged proximal pressure by 8.9 +/- 0.8 s. The distal pressure lagged the proximal pressure by 1.05 +/- 0.38 s. It is concluded that there is a significant variation in distal chloride activity, the magnitude of which appears to be sufficient to account for the observed flow variations through the operation of the tubuloglomerular feedback mechanism.