Impaired renorenal reflexes in spontaneously hypertensive rats.

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Abstract
In normotensive Sprague-Dawley rats stimulation of renal mechanoreceptors and chemoreceptors by increasing ureteral pressure and retrograde ureteropelvic perfusion with 0.9 M NaCl results in a contralateral inhibitory renorenal reflex response with contralateral diuresis and natriuresis. Since efferent renal nerve activity is increased in spontaneously hypertensive rats (SHR) and renal denervation delays the onset of hypertension in SHR in association with increased diuresis and natriuresis, the present study was undertaken to examine whether renorenal reflexes were altered in SHR compared with normotensive Wistar-Kyoto rats (WKY). In WKY mean arterial pressure was 113 .+-. 2 mm Hg and remained unchanged during renal mechanoreceptor and chemoreceptor stimulation. Increasing ureteral pressure 35 mm Hg increased ipsilateral afferent renal nerve activity 4.5 .+-. 1.7 resets/min, decreased contralateral efferent renal nerve activity 3.2 .+-. 0.8 resets/min, and increased contralateral urine flow rate 33 .+-. 4% and urinary sodium excretion 49 .+-. 8%. Similarly, retrograde ureteropelvic perfusion with 0.9 M NaCl increased ipsilateral afferent renal nerve activity 2.5 .+-. 0.6 resets/min, decreased contralateral efferent renal nerve activity 2.4 .+-. 1.1 resets/min, and increased contralateral urine flow rate 39 .+-. 5% and urinary sodium excretion 38 .+-. 8%. Stimulating renal mechanoreceptors and chemoreceptors to the same extent in SHR failed to increase ipsilateral afferent renal nerve activity, decrease contralateral efferent renal nerve activity, and produce a contralateral diuresis and natriuresis. It is concluded that renorenal reflexes are impaired in SHR. Failure of ipsilateral afferent renal nerve activity to increase during renal mechanoreceptor and chemoreceptor stimulation indicates a peripheral defect at the level of the renal sensory receptors. This abnormality in the renorenal reflex control of renal function may contribute to hypertension in SHR by promoting excess sodium and water retention.