Background & Aims: Although the β3 -adrenoceptor (AR) has been suggested to be involved in regulation of gut motility and visceral algesia, the precise mechanisms have been unknown. β3 -AR has been ...postulated to have a nonneuronal expression, being initially characterized in adipocytes and subsequently in the smooth muscle. We aimed to investigate the expression of β3 -AR in human enteric nervous system and its role in motility and visceral algesia. Methods: The expression of β3 -AR in human colon myenteric and submucosal plexus was investigated using immunohistochemistry. The effects of a β3 -AR agonist on nerve-evoked and carbachol-induced contractions as well as somatostatin release were investigated in strips of human colon. The effect of an agonist on diarrhea and visceral pain was investigated in vivo in rat models. Results: β3 -AR is expressed in cholinergic neurons in the myenteric plexus and submucosal plexus of human colon. Activation of β3 -AR causes the release of somatostatin from human isolated colon. In a rat model of visceral pain, β3 -AR agonist elicits somatostatin-dependent visceral analgesia. β3 -AR agonists inhibit cholinergically mediated muscle contraction of the human colon, as well as chemically induced diarrhea in vivo in a rat model. Conclusions: This is the first demonstration of expression of β3 -AR in the enteric nervous system. Activation of these receptors results in inhibition of cholinergic contractions and enhanced release of somatostatin, which may lead to visceral analgesia and inhibition of diarrhea. Therefore, β3 -AR could be a novel therapeutic target for functional gastrointestinal disorders.
Voltage-gated sodium channels play a fundamental role in determining neuronal excitability. Specifically, voltage-gated sodium channel subtype Na
1.7 is required for sensing acute and inflammatory ...somatic pain in mice and humans but its significance in pain originating from the viscera is unknown. Using comparative behavioural models evoking somatic and visceral pain pathways, we identify the requirement for Na
1.7 in regulating somatic (noxious heat pain threshold) but not in visceral pain signalling. These results enable us to better understand the mechanisms underlying the transduction of noxious stimuli from the viscera, suggest that the investigation of pain pathways should be undertaken in a modality-specific manner and help to direct drug discovery efforts towards novel visceral analgesics.
Voltage-gated sodium channel Na
1.7 is required for acute and inflammatory pain in mice and humans but its significance for visceral pain is unknown. Here we examine the role of Na
1.7 in visceral pain processing and the development of referred hyperalgesia using a conditional nociceptor-specific Na
1.7 knockout mouse (Na
1.7
) and selective small-molecule Na
1.7 antagonist PF-5198007. Na
1.7
mice showed normal nociceptive behaviours in response to intracolonic application of either capsaicin or mustard oil, stimuli known to evoke sustained nociceptor activity and sensitization following tissue damage, respectively. Normal responses following induction of cystitis by cyclophosphamide were also observed in both Na
1.7
and littermate controls. Loss, or blockade, of Na
1.7 did not affect afferent responses to noxious mechanical and chemical stimuli in nerve-gut preparations in mouse, or following antagonism of Na
1.7 in resected human appendix stimulated by noxious distending pressures. However, expression analysis of voltage-gated sodium channel α subunits revealed Na
1.7 mRNA transcripts in nearly all retrogradely labelled colonic neurons, suggesting redundancy in function. By contrast, using comparative somatic behavioural models we identify that genetic deletion of Na
1.7 (in Na
1.8-expressing neurons) regulates noxious heat pain threshold and that this can be recapitulated by the selective Na
1.7 antagonist PF-5198007. Our data demonstrate that Na
1.7 (in Na
1.8-expressing neurons) contributes to defined pain pathways in a modality-dependent manner, modulating somatic noxious heat pain, but is not required for visceral pain processing, and advocate that pharmacological block of Na
1.7 alone in the viscera may be insufficient in targeting chronic visceral pain.
Despite its beneficial effect in IBS patients, the mechanism of action of the 5-HT3 receptor (5-HT3R) antagonist alosetron is still incompletely understood. We aimed to characterize the effect and ...site(s) of action in a model of stress-induced sensitization of visceral nociception in rats. Adult male Wistar rats were equipped for recording of visceromotor response (VMR) to phasic colorectal distension (CRD; 10-60 mmHg). VMR to CRD was recorded 24 h after an acute session of water avoidance (WA) stress (post-WA). Baseline and post-WA responses were measured in rats exposed to WA or sham-WA, treated with alosetron at 0.3 mg/kg subcutaneously (s.c.) 25 nmol intrathecally (i.t.) or vehicle before post-WA CRD. Some rats were treated with capsaicin/vehicle on the cervical vagus nerve and received alosetron (0.3 mg/kg, s.c.) 15 min before post-WA CRD. WA stress led to visceral hyperalgesia 24 h later. Alosetron (0.3 mg/kg, s.c.), failed to inhibit WA-induced exacerbation of VMR to CRD. Stress-induced visceral hyperalgesia was abolished when alosetron was injected intrathecally (P<0.05) in intact rats or subcutaneously (0.3 mg/kg) in capsaicin-pretreated animals (P<0.05). Capsaicin-pretreatment did not affect the exacerbating effect of stress on visceral sensitivity. Alosetron had no inhibitory effect on normal visceral pain responses when administered subcutaneously or intrathecally. We demonstrated that 5-HT3Rs on central terminals of spinal afferents are engaged in the facilitatory effect of stress on visceral sensory information processing. In addition, we showed that stress-induced sensitization of visceral nociception is independent of 5-HT3R activation on vagal afferents.
P2Y receptors have been reported to modulate gastrointestinal functions. The newest family member is the nucleotide-sugar receptor P2Y14. P2ry14 mRNA was detected throughout the rat gut, with the ...highest level being in the forestomach. We investigated the role of the receptor in stomach motility using cognate agonists and knockout (KO) mice. In rat isolated forestomach, 100 microM UDP-glucose and 100 muM UDP-galactose both increased the baseline muscle tension (BMT) by 6.2+/-0.6 and 1.6+/-0.6 mN (P<0.05, n=3-4), respectively, and the amplitude of contractions during electrical field stimulation (EFS) by 3.7+/-1.7 and 4.3+/-2.5 mN (P<0.05, n=3-4), respectively. In forestomach from wild-type (WT) mice, 100 microM UDP-glucose increased the BMT by 1.0+/-0.1 mN (P<0.05, n=6) but this effect was lost in the KO mice (change of -0.1+/-0.1 mN, n=6). The 100 microM UDP-glucose also increased the contraction amplitude during EFS in this tissue from the WT animals (0.9+/-0.4 mN, P < 0.05, n=6) but not from the KO mice (0.0+/-0.2 mN, n=6). In vivo, UDP-glucose at 2,000 mg/kg ip reduced gastric emptying in rats by 49.7% (P<0.05, n=4-6) and in WT and KO mice by 56.1 and 66.2%, respectively (P<0.05, n=7-10) vs. saline-treated control animals. There was no significant difference in gastric emptying between WT and KO animals receiving either saline or d-glucose. These results demonstrate a novel function of the P2Y14 receptor associated with contractility in the rodent stomach that does not lead to altered gastric emptying after receptor deletion and an ability of UDP-glucose to delay gastric emptying without involving the P2Y14 receptor.
Herein we describe the medicinal chemistry programme to identify a potential back-up compound to the EP1 receptor antagonist GW848687X. This work started with the lipophilic 1,2-biaryl benzene ...derivative 4 which displayed molecular weight of 414.9 g/mol and poor in vivo metabolic stability in the rat and resulted in the identification of compound 7i (GSK345931A) which demonstrated good metabolic stability in the rat and lower molecular weight (381.9 g/mol). In addition, 7i (GSK345931A) showed measurable CNS penetration in the mouse and rat and potent analgesic efficacy in acute and sub-chronic models of inflammatory pain.
The release of calcitonin gene-related peptide (CGRP) plays a key role gastrointestinal tract homeostasis. We aimed to investigate mechanisms that mediate CGRP release from the rat colon
in vitro
. ...Colon segments were stimulated and the amount of CGRP released was measured using an enzyme immunoassay. Capsaicin and low pH induced significant increases in CGRP release which was shown to be mediated by TRPV1 activation as demonstrated with the TRPV1 antagonists CTPC and capsazepine. The mast cell degranulator, compound 48/80 significantly increased CGRP release an effect that was blocked in the presence of the mast cell stabilizer, ketotifen and the selective Gi inhibitor benzalkonium chloride. The addition of a mixture of inflammatory mediators containing pro-inflammatory cytokines, 5HT, bradykinin and PGE2 showed no effect at neutral pH but at low pH a significant additive effect was observed. We conclude that CGRP release in the rat distal colon occurs in response to mast cell degranulation, inflammatory mediators, low pH and capsaicin and describe a role for TRPV1 receptors in mediating the response.
A high-throughput screen targeting the EP(1) receptor identified non-acidic glycine sulfonamide derivative 2a with a pK(i) of 6.2. Analogue synthesis allowed a thorough investigation of the ...structure-activity relationship (SAR) and led to a 100-fold increase in recombinant potency.
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