Facilitatory role of efferent renal nerve activity on renal sensory receptors

The effects of decreasing and increasing efferent renal nerve activity (ERNA) on the renorenal reflex responses to stimulation of renal mechanoreceptors (MR) (increased ureteral pressure) or renal chemoreceptors (CR) (retrograde ureteropelvic perfusion with 0.9 M NaCl) were examined in anesthetized rats. During prevailing ERNA, renal MR stimulation increased ipsilateral afferent renal nerve activity (ARNA) from 6 to 41 counts/s (spike counter) (n = 37) and from 2 to 6 resets/min, (voltage integrator) (n = 23), contralateral urine flow rate from 5.3 to 7.4 microliters . min-1 . g-1 (n = 38) and urinary sodium excretion from 0.7 to 1.1 mumol . min-1 . g-1 (n = 38) (all P less than 0.01), without affecting mean arterial pressure or contralateral glomerular filtration rate. Similar results were obtained with renal CR stimulation. Decreasing ERNA 74 +/- 4% by hexamethonium, 10% body weight isotonic saline volume expansion, or inflation of a balloon at the junction of right atria and superior vena cava abolished the increase in ipsilateral ARNA and the contralateral diuresis and natriuresis produced by stimulation of renal MR or CR. Increasing ERNA 254 +/- 120% (peak response, n = 15, P less than 0.01) by placing the rat's tail in 53 degrees C water increased basal ARNA 249 +/- 80% (n = 6, P less than 0.05) and enhanced the ipsilateral ARNA response 202 +/- 78% (n = 9, P less than 0.01) to renal MR stimulation. These results indicate that ERNA exerts a facilitatory effect on renal MR and CR and their afferent renal nerve fibers in the renorenal reflexes.