Acute colonic inflammation triggers detrusor instability via activation of TRPV1 receptors in a rat model of pelvic organ cross-sensitization

Abstract

Chronic pelvic pain of unknown etiology is a common clinical condition and may develop as a result of cross-sensitization in the pelvis when pathological changes in one of the pelvic organs result in functional alterations in an adjacent structure. The aim of the current study was to compare transient receptor potential vanilloid 1 (TRPV1) activated pathways on detrusor contractility in vivo and in vitro using a rat model of pelvic organ cross-sensitization. Four groups of male Sprague-Dawley rats (N = 56) were included in the study. Animals received intracolonic saline (control), resiniferatoxin (RTX, TRPV1 agonist, 10(-7) M), 2,4,6-trinitrobenzene sulfonic acid (TNBS, colonic irritant), or double treatment (RTX followed by TNBS). Detrusor muscle contractility was assessed under in vitro and in vivo conditions. Intracolonic RTX increased the contractility of the isolated detrusor in response to electric field stimulation (EFS) by twofold (P ≤ 0.001) and enhanced the contractile response of the bladder smooth muscle to carbachol (CCh). Acute colonic inflammation reduced detrusor contractility upon application of CCh in vitro, decreased bladder capacity by 28.1% (P ≤ 0.001), and reduced micturition volume by 60% (P ≤ 0.001). These changes were accompanied by an increased number of nonmicturition contractions from 3.7 ± 0.7 to 15 ± 2.7 (N = 6 in both groups, P ≤ 0.001 vs. control). Desensitization of intracolonic TRPV1 receptors before the induction of acute colitis restored the response of isolated detrusor strips to CCh but not to EFS stimulation. Cystometric parameters were significantly improved in animals with double treatment and approximated the control values. Our data suggest that acute colonic inflammation triggers the occurrence of detrusor instability via activation of TRPV1-related pathways. Comparison of the results obtained under in vitro vs. in vivo conditions provides evidence that intact neural pathways are critical for the development of an overactive bladder resulting from pelvic organ cross talk.

Fig. 1.

Schematic presentation of the experimental design. A: time scale of the treatments and experimental end points during in vitro contractility studies. B: sequence of recordings of urodynamic parameters during cystometry in awake and freely moving rats. RTX, resiniferatoxin; TNBS, 2,4,6-trinitrobenzene sulfonic acid.

Fig. 2.

Hematoxylin and eosin (H&E) staining of the distal colon and urinary bladder from control and experimental animals. A: cross sections (10 μm) of the distal colon from control, RTX-treated, TNBS-treated, and RTX + TNBS-treated groups. In the group with TNBS treatment, please note the signs of colonic inflammation and tissue damage, including sites of hemorrhage and infiltration (arrow a), thickening of the muscle layer (arrow b), and disruption of the colonic crypts (arrow c). In the group with combined treatment (last panel), no significant tissue damage was observed except for mild thickening of the muscle layer (arrow d). B: cross sections of the urinary bladder from control, RTX-treated, TNBS-treated, and RTX + TNBS-treated groups. No visible alterations in the cytoarchitecture of the urinary bladder were observed after intracolonic treatments. All images were taken at X10 magnification. C: concentration of myeloperoxidase (MPO) enzyme in the distal colon from control and experimental groups. *P ≤ 0.05 vs. control.

Fig. 3.

Contractility of the detrusor muscle in response to electric field stimulation (EFS, 32 Hz) after acute experimental colitis. A: normalized maximal amplitude of the bladder muscle contractions in four experimental groups. B: the velocity of the contractile response (force slope) upon EFS. All results are presented as means ± SE. P values show the level of statistical significance between the groups.

Fig. 4.

Changes in the peak amplitude and contractile force slope of the detrusor muscle in vitro upon stimulation with 125 mM of potassium chloride (KCl). A: normalized peak amplitude of the detrusor muscle contractions in all experimental groups. B: the velocity of the contractile response upon stimulation with KCl. All results are presented as means ± SE. P values show the level of statistical significance between the groups.

Fig. 5.

The amplitude of bladder smooth muscle contractions in response to carbachol (CCh) in the control, TNBS, RTX, and double treatment (RTX + TNBS) groups. A: representative raw traces of detrusor contractions in response to 0.1–100 μM of CCh in the control group. B: representative raw traces of detrusor contractions in response to 0.1–100 μM of CCh in the group with acute experimental colitis. C: concentration-dependent contractile responses of the detrusor muscle in four experimental groups upon CCh stimulation. *P ≤ 0.05.

Fig. 6.

Representative traces of the cystograms recorded in awake and freely moving animals. No significant cystometric changes are observed before (A) and after (B) saline treatment in control animals. C (baseline cystogram) and D (during acute colonic inflammation) show the traces recorded in a rat from the group with acute colonic inflammation (3 days post-TNBS). This pattern of raw traces, including multiple nonmicturition contractions (NMC), was observed in all rats from the TNBS group. Arrows point at either micturition contractions (MC) in the control group (and at baseline) or NMC in the experimental colitis group. BP, bladder pressure; BC, bladder capacity; MV, micturition volume.

Fig. 7.

Analysis of urodynamic parameters recorded in conscious and unrestrained rats. A: comparison of the BC, MV, and intermicturition interval (IMI) in the control group, the group with acute colitis (TNBS), the group pretreated with intracolonic RTX (RTX group), and the double treatment group (RTX followed by TNBS-induced colitis). B: no. of NMC and micturition pressure (MP) measured at day 3 posttreatment in all experimental groups. P values show the level of statistical significance between the groups.