Experimental colitis triggers the release of substance P and calcitonin gene-related peptide in the urinary bladder via TRPV1 signaling pathways.

Clinical data provide evidence of high level of co-morbidity among genitourinary and gastrointestinal disorders characterized by chronic pelvic pain. The objective of this study was to test the hypothesis that colonic inflammation can impact the function of the urinary bladder via activation of TRPV1 signaling pathways followed by alterations in gene and protein expression of substance P (SP) and calcitonin gene-related peptide (CGRP) in sensory neurons and in the bladder. Inflammation was induced by intracolonic instillation of trinitrobenzene sulfonic acid (TNBS, 12.5mg/kg), and desensitization of TRPV1 receptors was evoked by intracolonic resiniferatoxin (RTX, 10(-)(7)M). mRNA and protein concentrations of CGRP and SP were measured at 3, 5 and 30 days. RTX instillation in the colon caused 3-fold up-regulation of SP mRNA in the urinary bladder at day 5 (n=7, p ≤ 0.05) followed by 35-fold increase at day 30 (n=5, p ≤ 0.05). Likewise, TNBS colitis triggered 15.8-fold up-regulation of SP mRNA 1 month after TNBS (n=5, p ≤ 0.05). Desensitization of colonic TRPV1 receptors prior to TNBS abolished SP increase in the urinary bladder. RTX led to 4.3-fold increase of CGRP mRNA at day 5 (n=7, p ≤ 0.05 to control) in the bladder followed by 28-fold increase at day 30 post-RTX (n=4, p ≤ 0.05). Colitis did not alter CGRP concentration during acute phase; however, at day 30 mRNA level was increased by 17.8 ± 6.9-fold (n=5, p ≤ 0.05) in parallel with 4-fold increase in CGRP protein (n=5, p ≤ 0.01) in the detrusor. Protein concentration of CGRP in the spinal cord was diminished by 45-65% (p ≤ 0.05) during colitis. RTX pretreatment did not affect CGRP concentration in the urinary bladder; however, it caused a reduction in CGRP release from lumbosacral DRG neurons during acute phase (3 and 5 days post-TNBS). Our results clearly demonstrate that colonic inflammation triggers the release of pro-inflammatory neuropeptides SP and CGRP in the urinary bladder via activation of TRPV1 signaling mechanisms enunciating the neurogenic nature of pelvic organ cross-sensitization.