Bradykinin and Protein Kinase C Activation Fail to Stimulate Renal Sensory Neurons in Hypertensive Rats

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Abstract
Abstract In normotensive rats, renal sensory receptor activation by increased ureteral pressure results in increased ipsilateral afferent renal nerve activity, decreased contralateral efferent renal nerve activity, and contralateral diuresis and natriuresis, a contralateral inhibitory renorenal reflex response. In spontaneously hypertensive rats (SHR), increasing ureteral pressure fails to increase afferent renal nerve activity. The nature of the inhibitory renorenal reflexes indicates that an impairment of the renorenal reflexes would contribute to the increased efferent renal nerve activity in SHR. We therefore examined whether there was a general decrease in the responsiveness of renal sensory receptors in SHR by comparing the afferent renal nerve activity responses to bradykinin in SHR and Wistar-Kyoto rats (WKY). In WKY, renal pelvic perfusion with bradykinin at 4, 19, 95, and 475 μmol/L increased afferent renal nerve activity by 1066±704, 2127±1121, 3517±1225, and 4476±1631%·second (area under the curve of afferent renal nerve activity versus time). In SHR, bradykinin at 4 to 95 μmol/L failed to increase afferent renal nerve activity. Bradykinin at 475 μmol/L increased afferent renal nerve activity in only 6 of 10 SHR. In WKY, renal pelvic perfusion with the phorbol ester 4β-phorbol 12,13-dibutyrate, known to activate protein kinase C, resulted in a peak afferent renal nerve activity response of 24±4%. However, 4β-phorbol 12,13-dibutyrate failed to increase afferent renal nerve activity in SHR. These findings demonstrate decreased responsiveness of renal pelvic sensory receptors to bradykinin in SHR. The impaired afferent renal nerve activity responses to bradykinin in SHR may be due to a lack of protein kinase C activation or a defect in the intracellular signaling mechanisms distal to protein kinase C activation.