ELECTRICALLY-INDUCED VASOMOTOR RESPONSES AND THEIR PROPAGATION IN RATRENAL VESSELS IN-VIVO

1. Vasomotor responses (VMR) induced by local electrical stimulation w ere studied in the vasculature of the split hydronephrotic rat kidney by in vivo microscopy. 2. Unipolar pulses, which mere applied by a mic ropipette positioned close to the vessel wall, elicited local and prop agated VMR. Depolarizing and hyperpolarizing currents caused vasoconst riction and vasodilatation, respectively. 3. The magnitude of VMR coul d be controlled within seconds by variation of pulse frequency, pulse width and voltage. VMR were abolished by slight retraction of the stim ulating micropipette. Repetitive electrical stimulation resulted in re producibly uniform VMR. 4. Propagated VMR decayed with increasing dist ance from the stimulation site. They decayed more rapidly in the upstr eam than in the downstream flow direction in interlobular arteries. Th e longitudinal decay was well approximated by an exponential function with significantly different length constants of 150 +/- 40 mu m (upst ream, n = 5) and 420 +/- 90 mu m (downstream, n = 8). 5. Our results s how that vasomotor responses, which are initiated by changes in membra ne potential, are propagated over distances of potential physiological importance in interlobular arteries.