Abstract
The pathogenesis of pain in irritable bowel syndrome (IBS) is poorly understood and treatment remains difficult. The present study was designed to investigate roles of adrenergic signaling and the endogenous hydrogen sulfide producing enzyme cystathionine β-synthetase (CBS) in a previously validated rat model of IBS induced by neonatal colonic inflammation (NCI). Here we showed that NCI-induced visceral hypersensitivity (VH) was significantly attenuated by β2 subunit inhibitor but not by β1 or β3 or α subunit inhibitor. NCI markedly elevated plasma norepinephrine (NE) concentration without alteration in expression of β2 subunit receptors in dorsal root ganglion (DRGs) innervating the colon. In addition, NCI markedly enhanced TRPV1 and CBS expression in the colon DRGs. CBS inhibitor AOAA reversed the upregulation of TRPV1 in NCI rats. In vitro experiments showed that incubation of DRG cells with NE markedly enhanced expression of TRPV1, which was reversed by application of AOAA. Incubation of DRG cells with the H2S donor NaHS greatly enhanced TRPV1 expression. Collectively, these data suggest that activation of adrenergic signaling by NCI sensitizes TRPV1 channel activity, which is likely mediated by upregulation of CBS expression in peripheral sensory neurons, thus contributing to chronic visceral hypersensitivity.
Highlights
Irritable bowel syndrome (IBS) is defined by recurrent symptoms of visceral pain or discomfort associated with alterations in bowel habits
In an agreement with previous report[8], abdominal withdrawal reflex (AWR) scores were significantly higher in neonatal colonic inflammation (NCI) rats at 20, 40, 60 and 80 mmHg distention pressures than those in age matched control rats (Fig. 1A, n = 8 for each group, *p < 0.05 vs. CON for the same pressure, MannWhitney test following Friedman ANOVA)
To determine whether adrenergic signaling is involved in NCI-induced visceral hypersensitivity (VH), non-selective adrenergic receptor inhibitors, propranolol (Prop) or phentolamine (Phen), was administered intraperitoneally (i.p.)
Summary
Irritable bowel syndrome (IBS) is defined by recurrent symptoms of visceral pain or discomfort associated with alterations in bowel habits. TRPV1 has been shown to play a significant role in both the initiation and the maintenance of visceral hypersensitivity in NCI rat model[11]. How these two molecules interact and whether adrenergic activation regulates expression of CBS and TRPV1 remain unknown under NCI conditions. We hypothesize that adrenergic signaling is involved in NCI-induced visceral hypersensitivity through sensitization of TRPV1 receptors by CBS-H2S signaling. To test this hypothesis, western blotting, patch clamp recordings, calcium imaging and behavioral studies were performed. Our findings implicate an important role for adrenergic signaling in IBS-like visceral hypersensitivity and identify the β 2 adrenergic receptors as a potential neurobiological target for the treatment of this symptom
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