ANALYSIS OF THE DYNAMICS OF RENAL VASCULAR-RESISTANCE AND URINE FLOW-RATE IN THE CAT FOLLOWING ELECTRICAL-STIMULATION OF THE RENAL NERVES

In ten sino-aortic denervated, vagotomized and aneasthetized cats, ren al efferent nerves were stimulated for 30 s with trains of constant cu rrent pulses at frequencies in the range 5-30 Hz. The arterial pressur e, heart rate, urine flow rate (electronic drop counter) and renal blo od flow (electromagnetic technique) were recorded. Subsequent computer processing gave the true means of renal artery pressure (MRAP) and re nal blood flow (MRBF) and hence the renal vascular resistance (MRVR), over each cardiac cycle. Recovery of MRVR after the end of stimulation exhibited two distinct time constants. The fast component had a time constant of 2.03 +/- 0.26 s and represented 60.2 +/- 1.71% of the reco very. The time constant of the slower component was 14.1 +/- 1.9 s and represented 36.0 +/- 1.6% of the recovery. The relationship between M RVR and stimulus frequency was sigmoidal with maximum sensitivity at s timulus frequencies of 12.6 +/- 0.76 Hz. Changes in urine flow rate, i n contrast, followed a hyperbolic function with maximum response sensi tivity occurring at very low stimulus frequencies. Changes in urine fl ow rate were 50% complete at stimulus frequencies of 5 Hz. Identificat ion of two distinct components in the relaxation phase of renal vascul ar resistance leads to a reasonable hypothesis that 60% of total renal vascular resistance may lie proximal to the glomerulus, whereas 36% m ay be accounted for by the efferent arterioles.