R-00493-2003.R1 Impaired substance P release from renal sensory nerves in SHR involves a pertussis toxin sensitive mechanism

Stretching the renal pelvic wall activates renal mechanosensory nerves by a PGE 2-mediated release of substance P via activation of the cAMP-PKA pathway. Renal pelvic angiotensin (ANG) II modulates the responsiveness of renal sensory nerves by suppressing the PGE 2-mediated activation of adenylyl cyclase via a PTX-sensitive mechanism. In SHR, activation of renal mechanosensory nerves is impaired. This is due to suppressed release of substance P in response to increased pelvic pressure. The present study was performed to investigate whether the PGE 2-mediated release of substance P was suppressed in SHR vs. WKY and if so, whether the impaired PGE 2-mediated release of substance P was due to ANG II activating a PTX sensitive mechanism. In an isolated renal pelvic wall preparation, PGE 2 , 0.14 :M, increased substance P release from 9±3 to 22±3 pg/min (P<0.01) in WKY, but had no effect in SHR. A tenfold higher concentration of PGE 2 , 1.4 :M, was required to increase substance P release in SHR, from 7±1 to 22±3 pg/min (P<0.01). In SHR, treating renal pelvises with losartan enhanced the release of substance P produced by subtreshold concentration of PGE 2 , 0.3 µM, from 16±2 to 26±3 pg/min (P<0.01). Likewise, treating renal pelvises with PTX enhanced the PGE 2 –mediated release of substance P from 10±1 to 33±3 pg/min (P<0.01) in SHR. In WKY, neither losartan nor PTX had an effect on the release of substance P produced by subthreshold concentrations of PGE 2 , 0.03 µM. Conclusion, the impaired responsiveness of renal sensory nerves in SHR involves endogenous ANG II suppressing the PGE 2-mediated release of substance P via a PTX sensitive mechanism.