Oxytocin (OT) is a nonapeptide of the neurohypophyseal protein family. The best establish actions of OT are to regulate uterine contractions during labor and the milk ejection reflex (Sala et al. 1974). Increasing number of reports indicate that both OT and OT receptor (OTR) are present throughout the gastrointestinal (GI) tract in human (Ohlsson et al. 2006), guinea pig (Yu et al. 2011), rabbit (Liu et al. 2003) and rat (Qin et al. 2009;Lv et al. 2010). Received October 24, 2011; revised manuscript received January 22, 2012; accepted February 8, 2012.Address correspondence and reprint requests to Dr Chuanyong Liu, Professor of Department of Physiology, Medical School of Shandong University, Jinan 250012, China. E-mail: liucy@sdu.edu.cnAbbreviations used: 2-APB, 2-Aminoethoxydiphenyl borate; AH, afterhyperpolarization; ENS, enteric nervous system; IPAN, intrinsic primary afferent neuron; LMMP, longitudinal muscle myenteric plexus; OT, oxytocin; OTR, oxytocin receptor; PBS, phosphate-buffered saline; PLC, phospholipase C; sAHP, slow after hyperpolarization. Abstract Oxytocin (OT) is clinically important in gut motility and constitutively reduces duodenum contractility. Intrinsic primary afferent neurons (IPANs), whose physiological classification is as AH cells, are the 1st neurons of the peristaltic reflex pathway. We set out to investigate if this inhibitory effect is mediated by IPANs and to identify the ion channel(s) and intracellular signal transduction pathway that are involved in this effect. Myenteric neurons were isolated from the longitudinal muscle myenteric plexus (LMMP) preparation of rat duodenum and cultured for 16-24 h before electrophysiological recording in whole cell mode and AH cells identified by their electrophysiological characteristics. The cytoplasmic Ca 2+ concentration ([Ca 2+ ] i ) of isolated neurons was measured using calcium imaging. The concentration of IP 3 in the LMMP and the OT secreted from the LMMP were measured using ELISA. The oxytocin receptor (OTR) and large-conductance calcium-activated potassium (BK Ca ) channels, as well as the expression of OT and the IPAN marker calbindin 28 K, on the myenteric plexus neurons were localized using double-immunostaining techniques. We found that administration of OT (10 )7 to 10 )5 M) dose dependently hyperpolarized the resting membrane potential and increased the total outward current. The OTR antagonist atosiban or the BK Ca channel blocker iberiotoxin (IbTX) blocked the effects of OT suggesting that the increased outward current resulted from BK Ca channel opening. OTR and the BK Ca a subunit were co-expressed on a subset of myenteric neurons at the LMMP. NS1619 (10 )5 M, a BK Ca channel activator) increased the outward current similar to the effect of OT. OT administration also increased [Ca 2+ ] i and the OT-evoked outward current was significantly attenuated by thapsigargin (10 )6 M) or CdCl 2 . The effect of OT on the BK Ca current was also blocked by pre-treatment with the IP 3 receptor antagonist 2-APB (10 )4 M) or ...

BACKGROUND AND PURPOSEH2S induces vasodilatation by opening KATP channels but it may also affect other ion channels. The aim of this study was to investigate the effect of H2S on intestinal motility in rats and its underlying mechanism. EXPERIMENTAL APPROACHThe tension of intestinal muscle strips, afferent firing of intestinal mesenteric nerves, length of duodenal smooth muscle cells and whole-cell membrane potential of dorsal root ganglion (DRG) neurons were monitored. H2S-producing enzymes were located by immunofluorescence staining. KEY RESULTSNaHS exerted early transient excitation and late long-lasting inhibition on the intestinal contraction. The excitation was attenuated by TRPV1 antagonists capsazepine, A784168, SB-366791 and NK1 receptor antagonist L703606, while the inhibition was attenuated by glibenclamide. NaHS increased duodenal afferent nerve firing and depolarized DRG neurons. These effects were reduced by capsazepine and A784168. NaHS relaxed isolated duodenal smooth muscle cells. The KATP channels were expressed in smooth muscle cells. Cystathionine β-synthase and cystathionine γ-lyase were expressed in rat duodenal myenteric neurons. L-cysteine and S-adenosyl-L-methionine increased the contraction of duodenal muscle strips, an effect attenuated by capsazepine and L703606. CONCLUSIONS AND IMPLICATIONSNaHS induces biphasic effects on intestinal motility in rats while endogenous H2S only exerts an excitatory effect. This transient excitatory effect might be mediated by activation of TRPV1 channels in sensory nerve terminals with the consequent release of substance P. The long-lasting inhibitory effect might be mediated by activation of KATP channels in the smooth muscle cells. These findings reveal a novel mechanism for the excitatory effect of H2S on gastrointestinal motility.

The aim of the present study was to investigate the effect of oxytocin (OT) on duodenum motility in rats and the possibility that cholecystokinin (CCK) was involved in this process. The isometric contraction of longitudinal muscle strips of duodenum was monitored by polygraph. ELISA was used to measure the concentration of CCK and OT in duodenum. CCK mRNA was assayed by RT-PCR. Oxytocin receptor (OTR) and CCK in duodenum were located by immunohistochemistry and immunofluorescence staining. OT (10⁻⁵ and 10⁻⁶ M) inhibited the spontaneous contraction of the muscle strips. On the contrary, atosiban (OT receptor antagonist), lorglumide (CCK₁ receptor antagonist), and tetrodotoxin (TTX, blocker of voltage-dependent Na(+) channel on nerve fiber) excited the contraction. The inhibitory effect of OT on duodenal motility was reversed by pretreatment of atosiban, lorglumide, or TTX. Exogenous OT did not influence the expression of OT mRNA in duodenum but increased the concentration of CCK in the culture medium of the cells isolated from longitudinal muscle myenteric plexus. The OTR and CCK were co-expressed in the neurons of the myenteric plexus in duodenum. We concluded that OT inhibited the contraction of the LD spontaneous contraction of rats in vitro. This effect was mediated by the CCK released from the neurons of the myenteric plexus in duodenum.

Background The aim of the current study was to investigate the effect of macrophage polarization on the expression of oxytocin (OT) and the oxytocin receptor (OTR) in enteric neurons. Methods In this study, we used a classic colitis model and D-mannose model to observe the correlation between macrophage polarization and OT signalling system. In order to further demonstrate the effect of macrophages, we examined the expression of OT signalling system after depletion of macrophages. Results The data showed that, in vitro, following polarization of macrophages to the M1 type by LPS, the macrophage supernatant contained proinflammatory cytokines (IL-1β, IL-6 and TNF-α) that inhibited the expression of OT and OTR in cultured enteric neurons; following macrophage polarization to the M2 type by IL4, the macrophage supernatant contained anti-inflammatory cytokines (TGF-β) that promoted the expression of OT and OTR in cultured enteric neurons. Furthermore, M1 macrophages decreased the expression of the OT signalling system mainly through STAT3/NF-κB pathways in cultured enteric neurons; M2 macrophages increased the expression of the OT signalling system mainly through activation of Smad2/3 and inhibition of the expression of Peg3 in cultured enteric neurons. In a colitis model, we demonstrated that macrophages were polarized to the M1 type during the inflammatory phase, with significant decreased in the expression of OT and OTR. When macrophages were polarized to the M2 type during the recovery phase, OT and OTR expression increased significantly. In addition, we found that D-mannose increased the expression of OT and OTR through polarization of macrophages to the M2 type. Conclusions This is the first study to demonstrate that macrophage polarization differentially regulates the expression of OT and OTR in enteric neurons.