Effects of acute administration of and tachyphylaxis to alpha,beta-methylene ATP in the guinea-pig small intestine

Evidence Supports Tradition: The in Vitro Effects of Roman Chamomile on Smooth Muscles

The dried flowers of Chamaemelum nobile (L.) All. have been used in traditional medicine for different conditions related to the spasm of the gastrointestinal system. However, there have been no experimental studies to support the smooth muscle relaxant effect of this plant. The aim of our research was to assess the effects of the hydroethanolic extract of Roman chamomile, its fractions, four of its flavonoids (apigenin, luteolin, hispidulin, and eupafolin), and its essential oil on smooth muscles. The phytochemical compositions of the extract and its fractions were characterized and quantified by HPLC-DAD, the essential oil was characterized by GC and GC-MS. Neuronally mediated and smooth muscle effects were tested in isolated organ bath experiments on guinea pig, rat, and human smooth muscle preparations. The crude herbal extract induced an immediate, moderate, and transient contraction of guinea pig ileum via the activation of cholinergic neurons of the gut wall. Purinoceptor and serotonin receptor antagonists did not influence this effect. The more sustained relaxant effect of the extract, measured after pre-contraction of the preparations, was remarkable and was not affected by an adrenergic beta receptor antagonist. The smooth muscle-relaxant activity was found to be associated with the flavonoid content of the fractions. The essential oil showed only the relaxant effect, but no contracting activity. The smooth muscle-relaxant effect was also detected on rat gastrointestinal tissues, as well as on strip preparations of human small intestine. These results suggest that Roman chamomile extract has a direct and prolonged smooth muscle-relaxant effect on guinea pig ileum which is related to its flavonoid content. In some preparations, a transient stimulation of enteric cholinergic motoneurons was also detected. The essential oil also had a remarkable smooth muscle relaxant effect in this setting. Similar relaxant effects were also detected on other visceral preparations, including human jejunum. This is the first report on the activity of Roman chamomile on smooth muscles that may reassure the rationale of the traditional use of this plant in spasmodic gastrointestinal disorders.

P2Y receptor-mediated transient relaxation of rat longitudinal ileum preparations involves phospholipase C activation, intracellular Ca(2+) release and SK channel activation

AIM

Purinergic signaling plays a major role in the enteric nervous system, where it governs gut motility through a number of P2X and P2Y receptors. The aim of this study was to investigate the P2Y receptor-mediated motility in rat longitudinal ileum preparations.

METHODS

Ileum smooth muscle strips were prepared from rats, and fixed in an organ bath. Isometric contraction and relaxation responses of the muscle strips were measured with force transducers. Drugs were applied by adding of stock solutions to the organ bath to yield the individual final concentrations.

RESULTS

Application of the non-hydrolyzable P2 receptor agonists α,β-Me-ATP or 2-Me-S-ADP (10, 100 μmol/L) dose-dependently elicited a transient relaxation response followed by a sustained contraction. The relaxation response was largely blocked by SK channel blockers apamin (500 nmol/L) and UCL1684 (10 μmol/L), PLC inhibitor U73122 (100 μmol/L), IP3 receptor blocker 2-APB (100 μmol/L) or sarcoendoplasmic Ca(2+) ATPase inhibitor thapsigargin (1 μmol/L), but not affected by atropine, NO synthase blocker L-NAME or tetrodotoxin. Furthermore, α,β-Me-ATP-induced relaxation was suppressed by P2Y1 receptor antagonist MRS2179 (50 μmol/L) or P2Y13 receptor antagonist MRS2211 (100 μmol/L), and was abolished by co-application of the two antagonists, whereas 2-Me-S-ADP-induced relaxation was abolished by P2Y6 receptor antagonist MRS2578 (50 μmol/L). In addition, P2Y1 receptor antagonist MRS2500 (1 μmol/L) not only abolished α,β-Me-ATP-induced relaxation, but also suppressed 2-Me-S-ADP-induced relaxation.

CONCLUSION

P2Y receptor agonist-induced transient relaxation of rat ileum smooth muscle strips is mediated predominantly by P2Y1 receptor, but also by P2Y6 and P2Y13 receptors, and involves PLC, IP3, Ca(2+) release and SK channel activation, but is independent of acetylcholine and NO release.

Traditional Chinese medicine Zhiqiao-Houpu herb-pair induce bidirectional effects on gastric motility in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Zhiqiao-Houpu herb-pair (ZQHPHP), composed of Fructus Aurantii (Zhiqiao [ZQ] in Chinese) and Magnolia officinalis (Houpu [HP] in Chinese), is a traditional herbal formula that has been extensively used for treating gastrointestinal motor dysfunction. The aim of the study was to evaluate the effect and possible mechanism of ZQHPHP on gastric emptying (GE) and gastric antral smooth muscle contractility (GASMC).

MATERIALS AND METHODS

This study includes four parts: (a) study of ZQHPHP's effect on GE; (b) study of ZQHPHP's effect on gastric antral smooth muscle contractility (GASMC); (c) comparing the effects of ZQHPHP, ZQ and HP on GASMC; (d) study of antagonists or agonists on ZQHPHP-induced GASMC. A test meal of Evans blue was adopted to estimate GE in rats. A polygraph was used to measure GASMC in rats.

RESULTS

The in vivo experiments demonstrated that, at the doses of 10mg/kg bw and 20mg/kg bw, ZQHPHP could promote GE. While, at the higher dose of 30 mg/kg bw, ZQHPHP delayed the GE. From the in vitro experiments we found that ZQHPHP (3-10 μg/ml) concentration-dependently increased the mean amplitude of contractions in the antral circular strip compared to untreated controls. While, in the concentration of 30 μg/ml, ZQHPHP prohibited GASMC. Besides, atropine blocked the stimulatory effect of ZQHPHP on GASMC and norepinephrine partly prohibited the stimulatory effect of ZQHPHP on GASMC, whereas isoproterenol showed no effect. From the in vitro experiment, we also found that ZQ and HP used together can synergistically increase gut motor.

CONCLUSIONS

The experiment indicated that ZQHPHP could induce bidirectional regulation on gastric motility. ZQ and HP used together can synergistically increase gut motor at a certain dosage. Lower dosage of ZQHPHP increases gastric motility, while higher dosage produces inhibition. In addition, the improvement of gastric motility by ZQHPHP is predominantly involved with muscarinic receptors and secondarily with alpha-receptors.

Purinergic signalling in the gastrointestinal tract and related organs in health and disease

Purinergic signalling plays major roles in the physiology and pathophysiology of digestive organs. Adenosine 5'-triphosphate (ATP), together with nitric oxide and vasoactive intestinal peptide, is a cotransmitter in non-adrenergic, non-cholinergic inhibitory neuromuscular transmission. P2X and P2Y receptors are widely expressed in myenteric and submucous enteric plexuses and participate in sympathetic transmission and neuromodulation involved in enteric reflex activities, as well as influencing gastric and intestinal epithelial secretion and vascular activities. Involvement of purinergic signalling has been identified in a variety of diseases, including inflammatory bowel disease, ischaemia, diabetes and cancer. Purinergic mechanosensory transduction forms the basis of enteric nociception, where ATP released from mucosal epithelial cells by distension activates nociceptive subepithelial primary afferent sensory fibres expressing P2X3 receptors to send messages to the pain centres in the central nervous system via interneurons in the spinal cord. Purinergic signalling is also involved in salivary gland and bile duct secretion.

Phytochemical Evaluation of Lythrum Salicaria Extracts and Their Effects on Guinea-Pig Ileum

n-Hexane, chloroform, ethyl acetate and 50% ethanol in water extracts prepared from the air-dried flowering parts of Lythrum salicaria L. were tested for in vitro pharmacological properties on Guinea-pig ileum, which is suitable for detecting a whole range of neuronal and smooth muscle effects. UHPLC-MS was used to evaluate polyphenol components of the extracts. In the ileum, the most prominent response (46.4% related to 0.5 μM histamine) of the extracts causing smooth muscle contractions were triggered by the 50% ethanol in water extract in a concentration-dependent manner. Atropine, indomethacin and PPADS plus suramin significantly reduced the contractile response caused by this extract. The strongest inhibition was due to atropine. The results suggest that L. salicaria extracts have a moderate muscarinic receptor agonist effect in Guinea-pig ileum and that prostanoids and purinoceptor mechanisms are involved to some extent. Therefore diluted extracts of L. salicaria p.o. could be used as a mild stimulant of gastrointestinal motility. The 50% ethanol in water extract was rich in polyphenols. n-Hexane, chloroform and ethyl acetate extracts failed to contain catechin, caffeic acid, quercetin-3-D-galactoside and rutin, but they all showed spasmogenic effects, and, therefore we do not think that these compounds could be involved in the spasmogenic activity.

The role of purinergic pathways in the pathophysiology of gut diseases: pharmacological modulation and potential therapeutic applications

Gut homeostasis results from complex neuro-immune interactions aimed at triggering stereotypical and specific programs of coordinated mucosal secretion and powerful motor propulsion. A prominent role in the regulation of this highly integrated network, comprising a variety of immune/inflammatory cells and the enteric nervous system, is played by purinergic mediators. The cells of the digestive tract are literally plunged into a "biological sea" of functionally active nucleotides and nucleosides, which carry out the critical task of driving regulatory interventions on cellular functions through the activation of P1 and P2 receptors. Intensive research efforts are being made to achieve an integrated view of the purinergic system, since it is emerging that the various components of purinergic pathways (i.e., enzymes, transporters, mediators and receptors) are mutually linked entities, deputed to finely modulating the magnitude and the duration of purinergic signaling, and that alterations occurring in this balanced network could be intimately involved in the pathophysiology of several gut disorders. This review article intends to provide a critical appraisal of current knowledge on the purinergic system role in the regulation of gastrointestinal functions, considering these pathways as a whole integrated network, which is capable of finely controlling the levels of bioactive nucleotides and nucleosides in the biophase of their respective receptors. Special attention is paid to the mechanisms through which alterations in the various compartments of the purinergic system could contribute to the pathophysiology of gut disorders, and to the possibility of counteracting such dysfunctions by means of pharmacological interventions on purinergic molecular targets.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Multiple motor effects of ATP and their inhibition by P purinoceptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid in the small intestine of the guinea-pig

Adenosine 5'-triphosphate (ATP) may be an important neurotransmitter in the gastrointestinal tract. The present study examined the motor effects of exogenous ATP on longitudinally-oriented preparations of the guinea-pig isolated ileum and the influence of drugs on the ATP-induced responses. High micromolar concentrations of ATP caused two types of contraction, a phasic, cholinergic response and a tonic, tetrodotoxin-resistant contraction. The phasic contraction was reduced by hexamethonium (5x10(-5) M), but left uninfluenced by capsaicin tachyphylaxis or tachyphylaxis to alpha,beta-methylene ATP. The tonic response was resistant to atropine, hexamethonium, capsaicin, omega-conotoxin GVIA, or pretreatment with alpha,beta-methylene ATP. Both types of ATP-induced contraction were diminished or abolished by the P2 purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 3x10(-6) and 3x10(-5) M, respectively). In the precontracted, atropine-treated ileum ATP (10(-6)-10(-4) M) caused guanethidine-resistant relaxation. This response was not influenced by tetrodotoxin, omega-conotoxin GVIA, or NG-nitro-L-arginine, but was abolished by apamin (10(-7) M), and inhibited by PPADS (3x10(-5) M) or reactive blue 2 (10(-5) M), in a surmountable manner. A high degree of tachyphylaxis was observed with the relaxant effect of ATP (10(-5)-10(-4) M). A high concentration (3x10(-4) M) of PPADS failed to influence ileum contractions to exogenous acetylcholine or histamine. It is concluded that, in addition to its direct contractile action in the guinea-pig ileum, ATP can activate (partly preganglionic) cholinergic neurones, an effect whose mechanism is largely different from that of alpha,beta-methylene ATP. ATP also causes relaxation by a direct, probably P2Y-receptor-mediated effect on the smooth muscle. All motor effects of ATP are inhibited by the antagonist PPADS.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).