Effect of the 5-HT receptor agonist tegaserod on the expression of GRK2 and GRK6 in the rat gastrointestinal tract.

Objective: Tegaserod is a 5-hydroxytryptamine type 4 (5-HT) receptor agonist, formerly used in treating constipation predominant irritable bowel syndrome, which desensitizes 5-HT receptors in rat oesophagus and colon in vitro. Desensitization of 5-HT receptors is regulated by G-protein coupled receptor kinases. This study was designed to assess the effect of 5-HT receptor activation on the expression of GRK2 and GRK6 in the rat oesophagus and distal colon by acute administration of tegaserod.

Distribution of 5-HT3, 5-HT4, and 5-HT7 Receptors Along the Human Colon.

Background/aims: Several disorders of the gastrointestinal tract are associated with abnormal serotonin (5-HT) signaling or metabolism where the 5-HT3 and 5-HT4 receptors are clinically relevant. The aim was to examine the distribution of 5-HT3, 5-HT4, and 5-HT7 receptors in the normal human colon and how this is associated with receptor interacting chaperone 3, G protein coupled receptor kin-ases, and protein LIN-7 homologs to extend previous observations limited to the sigmoid colon or the upper intestine.

Methods: Samples from ascending, transverse, descending, and sigmoid human colon were dissected into 3 separate layers (mucosa, lon-gitudinal, and circular muscles) and ileum samples were dissected into mucosa and muscle layers (n = 20).

Assessment of the pharmacological properties of 5-methoxyindole derivatives at 5-HT4 receptors.

Objectives: The aim was to examine the biological activity of 5-methoxytryptamine derivatives at the 5-hydroxytryptamine (5-HT)(4) receptor to explore the effect of substitution on the aliphatic amine of the 5-methoxyamine scaffold.

Methods: Three compounds were tested for affinity at the 5-HT(4) receptor by radioligand binding and functional activity using guinea-pig ileum and human colon circular muscle preparations and also in the mouse whole gut transit test.

Key Findings: The three compounds all had agonist properties at the 5-HT(4) receptor but their efficacy differed in the different functional tests.

Synthesis, testing and structure-activity studies on a library of 5-HT₄ ligands.

Several indole derivatives and analogues comprising a range of related structural classes were designed, synthesized and tested as ligands for the 5-HT₄ receptor. Within each series, binding experiments showed compounds with good affinity demonstrating high percentage displacement values at 1 µM. The most potent of these (20) had a pKi of 8.

Tissue dependent differences in G-protein coupled receptor kinases associated with 5-HT4 receptor desensitization in the rat gastro-intestinal tract.

Desensitization of 5-HT(4) receptors is regulated by G-protein coupled receptor kinases (GRKs). However, the specific GRK(s) that regulates the desensitization of 5-HT(4) receptors in the in vivo setting is unknown. We investigated the in situ expression of 5-HT(4) receptors and the GRKs in the rat gastrointestinal tract using immunohistochemistry and their interaction using coimmunoprecipitation.

Investigations into the binding affinities of different human 5-HT4 receptor splice variants.

This study examined whether the drug-receptor-binding sites of 5 selected human 5-HT(4) receptor splice variants [h5-HT4(a), h5-HT4(b), h5-HT4(c), h5-HT4(d) and h5-HT4(g)] display preferential affinities towards agonists. The agonists selected on the basis of chemical diversity and clinical relevance were: 5-HT4 benzamides, renzapride, zacopride and prucalopride; the benzimidazolones, DAU 6236 and BIMU 1; the aromatic ketone, RS67333, and the indole carbazimidamide tegaserod. The rank order of affinities ranging across the splice variants was: tegaserod (pKi: 7.

Cardioprotection induced by adenosine A1 receptor agonists in a cardiac cell ischemia model involves cooperative activation of adenosine A2A and A2B receptors by endogenous adenosine.

Extracellular adenosine concentrations increase within the heart during ischemia, and any exogenous adenosine receptor agonists therefore work in the context of significant local agonist concentrations. We evaluated the interactions between A1, A2A, A2B, and A3 receptors in the presence and absence of adenosine deaminase (ADA, which is used to remove endogenous adenosine) in a cardiac cell ischemia model. Simulated ischemia (SI) was induced by incubating H9c2(2-1) cells in SI medium for 12 hours in 100% N2 gas before assessment of necrosis using propidium iodide (5 microM) or apoptosis using AnnexinV-PE flow cytometry.

Synthesis and preliminary screening of novel indole-3-methanamines as 5-HT4 receptor ligands.

Twenty-three indole-3-methanamines were designed, synthesized and evaluated as ligands for the 5-HT(4) receptor. Compounds I-d, I-j, I-o, I-q and I-u showed good affinity at 100 microM and I-o was found to be only 5-fold less potent than the agonists serotonin (1) and 5-methoxytryptamine (2). Substitution on the 3-methanamine nitrogen clearly influenced activity with docking experiments into a homology model of the 5-HT(4) receptor showing a range of interactions with these side chain substituents.

Human 5-HT(4) and 5-HT(7) receptor splice variants: are they important?

G-protein-coupled receptors (GPCRs), which are encoded by >300 genes in the human genome, are by far the largest class of targets for modern drugs. These macromolecules display inherent adaptability of function, which is partly due to the production of different forms of the receptor protein. These are commonly called 'isoforms' or 'splice variants' denoting the molecular process of their production/assembly.

Effects of the novel 5-HT3 agonist MKC-733 on the rat, mouse and guinea pig digestive tract.

The contractile activity of the novel 5-HT(3) receptor agonist MKC-733 was determined in intestinal tissues of rats, guinea pigs and mice. The potential influence of non-5-HT(3) receptors was removed by the inclusion of methysergide and GR125487. MKC-733 had a lower efficacy than 5-HT in the rat jejunum, ileum and distal colon; however, it had similar efficacy and potency to 5-HT in the rat proximal colon.

Comparison of 5-HT4 and 5-HT7 receptor expression and function in the circular muscle of the human colon.

Serotonin receptors are potential targets for treating functional bowel disorders. This study investigated the functional roles and expression of the 5-HT4 and the 5-HT7 receptor, which coexist in human colon circular smooth muscle. 5-HT3 receptor expression was also investigated.

Activation of 5-HT3 receptors in the rat and mouse intestinal tract: a comparative study.

This study provides a comprehensive evaluation of 5-HT(3) receptor functional distribution in both the rat and mouse intestinal tract. 5-HT(3A-S) receptor splice variant mRNA was expressed throughout the intestine of the rat and mouse; the 5-HT(3A-L) variant being more common in the rat.5-HT, m-CPB, 1-PBG and 2-methyl-5-hydroxytryptamine (2m5-HT) induced contraction in the jejunum, ileum, proximal colon and distal colon of the rat (pEC(50) range: 2m5-HT, 5.

Identification of neurons that express 5-hydroxytryptamine4 receptors in intestine.

5-Hydroxytryptamine (5-HT) is an endogenous stimulant of intestinal propulsive reflexes. It exerts its effects partly through 5-HT4 receptors; 5-HT4 receptor agonists that are stimulants of intestinal transit are in clinical use. Both pharmacological and recent immunohistochemical studies indicate that 5-HT4 receptors are present on enteric neurons but the specific neurons that express the receptors have not been determined.

Comparison of opioid receptor distributions in the rat central nervous system.

The opioid receptors, mu, delta and kappa, conduct the major pharmacological effects of opioid drugs, and exhibit intriguing functional relationships and interactions in the CNS. Previously established hypotheses regarding the mechanisms underlying these phenomena specify theoretical patterns of relative cellular localisation for the different receptor types. In this study, we have used double-label immunohistochemistry to compare the cellular distributions of delta and kappa receptors with those of mu receptors in the rat CNS.

Optimization of a pharmacophore model for 5-HT4 agonists using CoMFA and receptor based alignment.

Twenty two 5-HT4 agonists obtained from our laboratory and the recent literature were used to develop a CoMFA model to predict 5-HT4 agonist activity. Two models were produced and compared for predictivity, the first by alignments based on atom overlapping (model A) and the second by adding agonist binding site interacting points of the 5-HT4 receptor (model B). Comparison of the two models showed that the q2 value for model A was 0.

Characterisation of opioid receptors involved in modulating circular and longitudinal muscle contraction in the rat ileum.

1. The aim of the present investigation was to characterise the opioid receptor subtypes present in the rat ileum using a method that detects drug action on the enteric nerves innervating the circular and longitudinal muscles. 2.

Effects of tachykinins and 5-hydroxytryptamine on intestinal secretion.

1. The main aim of the present study was to establish the functional in vivo effects of tachykinins on net fluid transport by the jejunum and ileum of anaesthetized rats. Tachykinins were administered by retrograde infusion in saline into the left common carotid artery.

Effects of some antidepressant drugs on tryptaminergic responses of the rat jejunum.

The rat isolated jejunum was used as a functional model to screen some antidepressant drugs at the "atypical" 5-HT(7) receptor. Mianserin acted as a surmountable antagonist of 5-CT with a PA(2) value of 8.22 +/- 0.

Effects of adenosine agonists on consumptive behaviour and body temperature.

This study was designed to determine the effects of the A1-receptor selective agonist N6-cyclopentyladenosine (CPA), and the A2-selective agonist, 2-p-(2-carboxyethyl)-phenethylamino-5'-N-ethylcarboxamidoadenosine-hydrochloride (CGS-21680) on consumptive behaviour and body temperature in rats in relation to the non-selective A1/A2 adenosine agonist, N-ethylcarboxamidoadenosine (NECA), and to morphine. It was shown that two subcutaneous injections of 0.1 and 0.