Impaired Renorenal Reflexes in Two-Kidney, One Clip Hypertensive Rats

In normotensive rats, stimulation of renal mechanoreceptors by an increase in ureteral pressure results in a contralateral inhibitory renorenal reflex response with contralateral natriuresis. Similar effects are produced by stimulation of renal chemoreceptors by renal pelvic perfusion with 0.9 M NaCl. However, in spontaneously hypertensive rats the renorenal reflex responses to renal mechanoreceptor and chemoreceptor stimulation are impaired. The present study was performed to examine whether the renorenal reflexes were altered in two-kidney, one clip hypertensive rats, a model of hypertension in which it has been suggested that the afferent renal nerves contribute to the enhanced peripheral sympathetic nervous activity. A 0.2 mm silver clip was placed around one renal artery 4 weeks before the study. At the time of study, mean arterial pressure was 156 ±4 mm Hg. Renal mechanoreceptor and chemoreceptor stimulation of either the nonclipped or clipped kidney failed to affect ipsilateral afferent renal nerve activity, contralateral efferent renal nerve activity, and contralateral urine flow rate and urinary sodium excretion. Renal denervation of the nonclipped kidney increased ipsilateral urinary sodium excretion from 0.65 ±0.13 to 1.50±0.42 μmol/min/g and decreased contralateral urinary sodium excretion from 0.18 ±0.03 to 0.13 ±0.03 μmol/min/g (p < 0.05). Thus, denervation of the nonclipped kidney resulted in a similar contralateral excitatory renorenal reflex response as in normotensive rats. However, denervation of the clipped kidney increased both ipsilateral and contralateral urinary sodium excretion, from 0.14±0.04 to 0.27±0.5 μmol/min/g and from 1.29±0.33 to 2.09±0.59 μmol/min/g (p < 0.01), respectively. Taken together these data suggest that the lack of inhibitory renorenal reflexes from the clipped kidney may enhance efferent sympathetic nervous activity and thereby contribute to the hypertension in two-kidney, one clip hypertensive rats.