5-hydroxytryptamine (5-HT) is involved in the stress-induced alteration of colonic functions, specifically motility and secretion, but its precise mechanisms of regulation remain unclear. In the present study, we have investigated the effects of 5-HT on rat colonic mucosal secretion after acute water immersion restraint stress, as well as the underlying mechanism of this phenomenon, using short circuit current recording (ISC), real-time polymerase chain reaction, Western blot analysis, and enzyme-linked immunosorbance assays. After 2 h of water immersion restraint stress, the baseline ISC and 5-HT-induced ISC responses of the colonic mucosa were significantly increased. Pretreatment with selective 5-HT4 receptor antagonist, SB204070, inhibited the 5-HT-induced colonic ISC response by 96 % in normal rats and 91.2 % in acute-stress rats. However, pretreatment with the selective antagonist of 5-HT3 receptor, MDL72222 or Y-25130, had no obvious effect on 5-HT-induced ISC responses under either set of conditions. Total protein expression of both the mucosal 5-HT3 receptors and the 5-HT4 receptors underwent no significant changes following acute stress. Both colonic basal cAMP levels and foskolin-induced ISC responses were significantly enhanced in acute stress rats. 5-HT significantly enhanced the intracellular cAMP level via 5-HT4 receptors in the colonic mucosa from both control and stressed animals, and 5-HT-induced cAMP increase in stressed rats was not more than that in control rats. Taken together, the present results indicate that acute water immersion restraint stress enhances colonic secretory responses to 5-HT in rats, a process in which increased cellular cAMP accumulation is involved., Y. Li, L. S. Li, X. L. Zhang, Y. Zhang, J. D. Xu, J. X. Zhu., and Obsahuje bibliografii
The purpose of this study was to elucidate the intestinal serotonin (5-HT) receptor subtypes involved in fluid transport in the pig jejunum in uioo. The fluid accumulating effect of intraluminally administered 5-HT, renzapride, methysergide, ketanserin, granisetron, citalopram and intravenous indomethacin, was tested in tied- off loops in uiuo. 5-HT caused a dose-dependent fluid accumulation, which was reduced by indomethacin by about 30 %. Renzapride, methysergide, ketanserin, granisetron and citalopram all caused fluid accumulation. Taking into account these fluid accumulating effects, renzapride, methysergide, ketanserin and granisetron reduced the fluid accumulating effect of 5-HT, giving a maximal reduction of 70, 46, 76, and 80 %, respectively. These data suggest the existence of intestinal 5-HT receptor subtypes involved in fluid transport in the pig jejunum. The antagonistic effects of indomethacin, ketanserin and granisetron, suggest the involvement of prostangladins, as well as the 5-HT2 and the 5-HT3 receptor subtypes in the fluid accumulating response of 5-HT.
The physiological significance of serotonin released into the intestinal lumen for the regulation of motility is unknown in humans. The aim of this study was to evaluate the effect of serotonin infused into the lumen of the gastric antrum, duodenum or the jejunum, on antro-duodeno-jejunal contractility in healthy human volunteers. Manometric recordings were obtained and the effects of either a standard meal, continuous intravenous infusion of serotonin (20 nmol/kg/min) or intraluminal bolus infusions of graded doses of serotonin (2.5, 25 or 250 nmol) were compared. In addition, platelet-depleted plasma levels of serotonin, blood pressure, heart rate and electrocardiogram were evaluated. All subjects showed similar results. Intravenous serotonin increased migrating motor complex phase III frequency 3-fold and migrating velocity 2-fold. Intraluminal infusion of serotonin did not change contractile activity. Platelet-depleted-plasma levels of serotonin increased 2-fold following both intravenous and high doses of intraluminal infusions of serotonin. All subjects reported minor short-lived adverse effects following intravenous serotonin stimulation, while only half of the subjects reported minor short-lived adverse effects following intraluminal serotonin stimulations. We conclude that exogenous serotonin in the lumen of the upper part of the small intestine does not seem to change antro-duodeno-jejunal contractility significantly in healthy adult volunteers., M. B. Hansen, F. Arif, H. Gregersen, H. Bruusgaard, L. Wallin., and Obsahuje bibliografii a bibliografické odkazy
This review presents recent findings regarding the physiological and pathophysiological extra- and intracellular mechanisms of secretory diarrhoea. Putative interventions directed towards counteracting the mechanisms causing fluid loss, especially in relation to the enteric nervous system, intracellular mediators, and localization of fluid and electrolyte transport, are discussed. The enteric nervous system regulates the complex process of transmural fluid and electrolyte transport by controlling the function of the mucosa, the motility, and the microcirculation in both health and disease. Most of the processes, leading to secretory diarrhoea, involve activation of the enteric nervous system, with local release of neurotransmitters and other endogenous effectors, which induce chloride secretion. A new therapeutic approach is based on stimulation of absorption and inhibition of secretion by using receptor agonists and antagonists, and modulators of intracellular signal transduction. A physio-pharmacological review of serotonin and the antisecretory factor as modulators of intestinal fluid and electrolyte transport is given.
5-Hydroxytryptamine (5-HT) can be released from mast cells and platelets through an IgE-dependent mechanism and may play a role in the pathogenesis of allergic bronchoconstriction. However, the effect of 5-HT on ion transport by the airway epithelium is still controversial. The objective of this study was to determine whether 5-hydroxytryptamine (5-HT) regulates NaCl transport by different mechanisms in the apical and basolateral membrane of tracheal epithelia. We studied the rat tracheal epithelium under short-circuit conditions in vitro. Short-circuit current (Isc) was measured in rat tracheal epithelial monolayers cultured on porous filters. 5-HT inhibited Na+ absorption [measured via Na+ short-circuit current (INasc)] in the apical membrane and stimulated Cl- secretion [measured via Cl- short-circuit current (IClsc)] in the basolateral membrane. Functional localization using selective 5-HT agonists and antagonists suggest that IClsc is stimulated by the basolateral membrane-resident 5-HT receptors, whereas INasc is inhibited by the apical membrane-resident 5-HT2 receptors. The basolateral addition of 5-HT increases intracellular cAMP content, but its apical addition does not. The addition of BAPTA/AM blocked the decrease of INasc which was induced by the apical addition of 5-HT, and 5-HT increased intracellular Ca concentrations. These results indicate that 5-HT differentially affects INasc and IClsc across rat tracheal monolayers through interactions with distinct receptors in the apical and the basolateral membrane. These effects may result in an increase of water movement towards the airway lumen.