Abstract-In normotensive rats, increased renal pelvic pressure stimulates the release of prostaglandin E and substance P, which in turn leads to an increase in afferent renal nerve activity (ARNA) and a contralateral natriuresis, a contralateral inhibitory renorenal reflex. In spontaneously hypertensive rats (SHR), increasing renal pelvic pressure failed to increase afferent renal nerve activity. The inhibitory nature of renorenal reflexes indicates that impaired renorenal reflexes could contribute to increased sodium retention in SHR. Phorbol esters, known to activate protein kinase C, increase afferent renal nerve activity in Wistar-Kyoto rats (WKY) but not in SHR. We examined the mechanisms involved in the impaired responses to renal sensory receptor activation in SHR. The phorbol ester 4-phorbol 12,13-dibutyrate increased renal pelvic protein kinase C activity similarly in SHR and WKY. Increasing renal pelvic pressure increased afferent renal nerve activity in WKY (27Ϯ2%) but not in SHR. Renal pelvic release of prostaglandin E increased similarly in WKY and SHR, from 0.8Ϯ0.1 to 2.0Ϯ0.4 ng/min and 0.7Ϯ0.1 to 1.4Ϯ0.2 ng/min. Renal pelvic release of substance P was greater (PϽ.01) in WKY, from 16.3Ϯ3.8 to 41.8Ϯ7.4 pg/min, than in SHR, from 9.9Ϯ1.7 to 17.0Ϯ3.2 pg/min. In WKY, renal pelvic administration of substance P at 0.8, 4, and 20 g/mL increased ARNA 382Ϯ69, 750Ϯ233, and 783Ϯ124% ⅐ second (area under the curve of afferent renal nerve activity versus time). In SHR, substance P at 0.8 to 20 g/mL failed to increase ARNA. These findings demonstrate that the impaired afferent renal nerve activity response to increased renal pelvic pressure is related to decreased release of substance P and/or impaired activation of substance P receptors. (Hypertension. 1998;31:815-822.)Key Words: afferent renal nerve activity Ⅲ receptors, sensory Ⅲ prostaglandins Ⅲ protein kinase C Ⅲ substance P Ⅲ rats, inbred SHR O bstruction to urine flow increases renal pelvic pressure and activates renal mechanoreceptors, resulting in an increase in ipsilateral ARNA.1-5 The increase in ARNA produces a fall in contralateral efferent renal sympathetic nerve activity (ER-SNA) and a contralateral diuresis and natriuresis, known as the contralateral inhibitory renorenal reflex.
2Accumulating evidence indicates that the renal nerves contribute to the pathogenesis of hypertension in SHR.6 Peripheral sympathetic nerve activity and, in particular, ERSNA is enhanced in SHR. The nature of the renorenal reflex, that is, a diuresis and natriuresis in association with decreased ERSNA, would suggest that an attenuation of this reflex would result in increased ERSNA leading to water and sodium retention, factors known to contribute to the hypertensive process. 7 Our previous studies in SHR demonstrated that increasing renal pelvic pressure failed to increase ARNA and thus failed to elicit a contralateral renorenal reflex in these rats. 8 The lack of an increase in ARNA in response to increased renal pelvic pressure suggested that the impairment of the reno...