Gastrointestinal smooth muscle effect

Histamine is able to cause uterine contraction. Although the magnitude of this effect in humans is normally small, the large amounts of histamine released during anaphylactic reactions can initiate abortion in pregnant women. Histamine can also stimulate contraction of gastrointestinal smooth muscle, with large doses able to produce diarrhea. 

The postsynaptic physiological effects of serotonin are varied and widespread. The administration of serotonin leads to powerful smooth-muscle effects in the cardiovascular and gastrointestinal systems. Vasodilation and hypotension may result, partly through central effects, if the serotonin concentration in the CNS is increased by administration of the serotonin precursor 5-hydroxytryptophan. Unlike serotonin, this precursor can cross the blood-brain barrier. Intestinal mobility is also influenced by serotonin. 

Hi receptor antagonists block the actions of histamine by reversible competitive antagonism at the Hi receptor. They have negligible potency at the H2 receptor and little at the H3 receptor. For example, histamine-induced contraction of bronchiolar or gastrointestinal smooth muscle can be completely blocked by these agents, but the effects on gastric acid secretion and the heart are unmodified. 

The peripheral effects concern the motility and tonus of gastrointestinal smooth muscle segmentation is enhanced but propulsive peristalsis is inhibited. The tonus of sphincter muscles is markedly raised (spastic constipation). The antidiarrhetic effect is used therapeutically (loperamide, p.180). Gastric emptying is delayed (pyloric spasm) and drainage of bile and pancreatic juice is impeded because the sphincter of Oddi contracts. Likewise, bladder function is affected specifically bladder emptying is impaired owing to an increased tone of the vesicular sphincter. 

Motilin is a neuropeptide expressed predominantly in the gastrointestinal tract that stimulates the contraction of gastrointestinal smooth muscle throughout the gut (Tonini 1996). Physiologically, its most characteristic role seems to be the induction of coordinated interdigestive antral and duodenal contractions (phase III of the migrating motor complex). The effects of motilin are both species and dose dependent. Motilin appears to have at least two receptors, one muscular and the other neuronal. Recent studies in vivo have emphasized the importance of the latter pathway and it is currently hypothesized that motilin acts on neurons in the myenteric plexus to release acetylcholine and other excitatory neurotransmitters. 

Bethanechol is a synthetic cholinergic agonist (P-methyl analog of carbachol) that has parasympathomimetic effects in gastrointestinal smooth muscle and in the detrusor muscle. It has... 

Dicycloverine and atropine are antimuscarinic drugs included in some indigestion medicines to relieve colic. They exert a relaxant effect on gastrointestinal smooth muscle and inhibit gastric secretion. 

EM also has a motilin-like stimulating activity on gastrointestinal smooth muscles [39]. Therefore, the inhibitory effect on cytokine expression in human cells summarized here may be a third bioactivity of the macrolide antibiotic. We recently reported that some of these derivatives have inhibitory effect on IL-8 production by human airway epithelial cells [72], These analogues also showed inhibitory action on the activation of NFkB and AP-1 assessed by EMSA (M. Desaki etal., unpublished observations, January 2001). Characterization of the chemical structure responsible for its potential would be important to pursue and further investigation for the molecular mechanism would be necessary for a possible new type of anti-inflammatory agent. 

Both phentolamine and tolazoline are potent but rather nonspecific a-antagonists. Both drugs stimulate gastrointestinal smooth muscle, an action blocked by atropine, which would indicate cholinergic activity, and they both stimulate gastric secretion, possibly through release of histamine. Because of these and other side effects, the clinical applications of tolazoline and phentolamine also are limited to treating the symptoms of pheochromocytoma. 

BIOLOGICAL ACTIONS Gastrointestinal smooth muscle Reproductive smooth muscle Respiratory smooth muscle Cardiovascular system Blood platelet aggregation Metabolic effects... 

The mechanism of action of prostaglandins on gastrointestinal smooth muscle has been investigated by several authors [216, 221-225] and is reviewed by Horton [13] and Pickles [10]. It is suggested that PGEi exerts its effect by a direct action on the cell membrane [222], but observations that certain responses are reduced by nerve-blocking drugs, for example, atropine, point to the possibility that there is some element of mediation via a nervous pathway [223],... 

Sesearoh on this topic is far from complete In order to have an suiequate idea of the actions of caerulein on the gastrointestinal smooth muscle it will be necessary to study comparatively the effects of the polypeptide on the different sections of the gut of various animal species and to elucidate the mechanism which is at the root of these effeots.lt iS)in fact) likely that some actions of caerulein are direct actions on the smooth muscle)but others are mediated througdi the central or peripheral nervous system ... 

There are a number of side-effects of opiates that are due to their actions on opiate receptors outside the central nervous system. Opiates constrict the pupils by acting on the oculomotor nucleus and cause constipation by activating a maintained contraction of the smooth muscle of the gut which reduces motility. This diminished propulsion coupled with opiates reducing secretion in the gut underlie the anti-diarrhoeal effect. Opiates contract sphincters throughout the gastrointestinal tract. Although these effects are predominantly peripheral in origin there are central contributions as well. Morphine can also release histamine from mast cells and this can produce irritation and broncho-spasm in extreme cases. Opiates have minimal cardiovascular effects at therapeutic doses. 

AMOS s, OKWUASABA F K, GAMANIEL K, AKAH P, WAMBEBE c (1998) Inhibitory effects of the aqueous extract of Pavetta crassipes leaves on gastrointestinal and uterine smooth muscle preparations isolated from rabbits, guinea pigs and rats. J Ethnopharmacol. 61 209-13. 

Two membrane-receptive binding sites called and receptors mediate the pharmacological effect of histamine. Hj receptors are located in smooth muscle of vessels, and bronchial and gastrointestinal tract, while H2 receptors are found in the walls of the stomach, myocardium, and certain vessels. 

All smooth muscle activity which is physiologically under a strong parasympathetic influence is effectively inhibited by atropine, for example in the gastrointestinal, genitourinary and respiratory tract. Parasympatholytics are very useful drugs in the treatment of spastic conditions (colic) in these regions. 

Dopamine is an intermediate product in the biosynthesis of noradrenaline. Furthermore it is an active transmitter by itself in basal ganglia (caudate nucleus), the nucleus accumbens, the olfactory tubercle, the central nucleus of the amygdala, the median eminence and some areas in the frontal cortex. It is functionally important, for example in the extra-pyramidal system and the central regulation of emesis. In the periphery specific dopamine receptors (Di-receptors) can be found in the upper gastrointestinal tract, in which a reduction of motility is mediated, and on vascular smooth muscle cells of splanchnic and renal arteries. Beside its effect on specific D-receptors, dopamine activates, at higher concentrations, a- and -adrenoceptors as well. Since its clinical profile is different from adrenaline and noradrenaline there are particular indications for dopamine, like situations of circulatory shock with a reduced kidney perfusion. Dopamine can dose-dependently induce nausea, vomiting, tachyarrhythmia and peripheral vasoconstriction. Dopamine can worsen cardiac ischaemia. 

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