Activity Of Longitudinal Muscle Strips Research Articles

A verification study of gastrointestinal motility-stimulating action of guinea-pig motilin using isolated gastrointestinal strips from rabbits and guinea-pigs

Motilin (MLN), a 22-amino-acid peptide hormone, is generally present in the mucosa of the upper gastrointestinal (GI) tract, mainly the duodenum of mammals, and it regulates GI motility, especially that related to interdigestive migrating contraction. However, MLN and its receptor are absent in mice and rats, and MLN does not cause any mechanical responses in the rat and mouse GI tracts. The guinea-pig is also a rodent, but expression of the MLN gene in the guinea-pig has been reported. In the present study, two guinea-pig MLNs, FIPIFTYSELRRTQEREQNKGL found in the Ensemble Genome Database (gpMLN-1) and FVPIFTYSELRRTQEREQNKRL reported by Xu et al. (2001) (gpMLN-2), were synthesized, and their biological activities were evaluated in the rabbit duodenum and guinea-pig GI tract in vitro. Both gpMLNs showed contractile activity in longitudinal muscle strips of the rabbit duodenum. The EC50 values of gpMLN-1 and gpMLN-2 were slightly higher than that of human MLN (hMLN), but the maximum contractions were as same as that of hMLN. Treatment with GM109 and hMLN-induced receptor desensitization decreased the contractile activity of both gpMLNs, indicating that the two gpMLN candidates are able to activate the MLN receptor (MLN-R) of the rabbit duodenum. In guinea-pig GI preparations, hMLN and gpMLNs did not show any mechanical responses in circular muscle strips from the gastric antrum or in longitudinal strips of the duodenum, ileum and colon although acetylcholine and 1,1-dimethyl-4-phenylpiperazinium (DMPP) caused definite mechanical responses. The DMPP-induced neural responses in the gastric circular muscle and ileal longitudinal muscles were not modified by gpMLN-1. Even in the gastric and ileal strips with intact mucosa, no mechanical responses were seen with either of the gpMLNs. Furthermore, RT-PCR using various primer sets failed to amplify the gpMLN-2 mRNA. In conclusion, gpMLNs including one that was already reported and the other that was newly found in a database were effective to the rabbit MLN-R, whereas they did not cause any contractions or modification of neural responses in the guinea-pig GI tract, indicating that the MLN system is vestigial and not functional in regulation of GI motility in the guinea-pig as well as in other rodents such as rats and mice.

In vivo and in vitro evaluation of the effects of domperidone on the gastrointestinal tract of healthy horses

To determine the effects of domperidone on in vivo and in vitro measures of gastrointestinal tract motility and contractility in healthy horses. 18 adult horses and tissue samples from an additional 26 adult horses. Domperidone or placebo paste was administered to healthy horses in a 2-period crossover study. Gastric emptying was evaluated after oral administration of domperidone paste (1.1 or 5.0 mg/kg) or placebo paste by means of the acetaminophen absorption test in 12 horses. Frequency of defecation, weight of feces produced, fecal moisture, and stomach-to-anus transit time of microspheres were evaluated after administration of domperidone paste (1.1 mg/kg) or placebo paste in 6 horses. The effect of domperidone on smooth muscle contractile activity in samples of duodenum, jejunum, ileum, or colon obtained from 26 horses immediately after euthanasia (for nonsystemic medical problems) was investigated. Oral administration of 5.0 mg of domperidone/kg increased peak plasma acetaminophen concentration and area under the curve, indicating increased gastric emptying. Administration of 1.1 mg of domperidone/kg had no effect on gastric emptying, transit time, defecation frequency, or amount and moisture of excreted feces. Contractile activities of circular and longitudinal muscle strips from the duodenum, jejunum, ileum, or colon were not altered by domperidone. Dopamine increased contractile activity of longitudinal muscle strips but not that of circular muscle strips from the midjejunum. Domperidone decreased the dopamine-induced contractile activity of midjejunal longitudinal muscle strips. The potential beneficial effects of domperidone in horses with ileus need to be evaluated in horses with decreased gastric emptying or adynamic ileus.

Role of Selective α and β Adrenergic Receptor Mechanisms in Rat Jejunal Longitudinal Muscle Contractility

Gut motility is modulated by adrenergic mechanisms. The aim of our study was to examine mechanisms of selective adrenergic receptors in rat jejunum. Spontaneous contractile activity of longitudinal muscle strips from rat jejunum was measured in 5-ml tissue chambers. Dose–responses (six doses, 10−7–3 × 10−5M) to norepinephrine (NE, nonspecific), phenylephrine (PH, α1), clonidine (C, α2), prenalterol (PR, β1), ritodrine (RI, β2), and ZD7714 (ZD, β3) were evaluated with and without tetrodotoxin (TTX, nerve blocker). NE(3 × 10−5M) inhibited 74 ± 5% (mean ± SEM) of spontaneous activity. This was the maximum effect. The same dose of RI(β2), PH(α1), or ZD(β3) resulted in an inhibition of only 56 ± 5, 43 ± 4, 33 ± 6, respectively. The calculated concentration to induce 50% inhibition (EC50) of ZD(β3) was similar to NE, whereas higher concentrations of PH(α1) or RI(β2) were required. C(α2) and PR(β1) had no effect. TTX changed exclusively the EC50 of RI from 4.4±0.2 to 2.7 ± 0.8% (p < 0.04). Contractility was inhibited by NE (nonspecific). PH(α1), RI(β2), and ZD(β3) mimic the effect of NE. TTX reduced the inhibition by RI. Our results suggest that muscular α1, β2, and β3 receptor mechanisms mediate adrenergic inhibition of contractility in rat jejunum. β2 mechanisms seem to involve also neural pathways.

Effect of TNBS-induced morphological changes on pharmacological contractility of the rat ileum

Intraluminal instillation of 2,4,6-trinitrobenzene sulfonic acid (TNBS) in ethanol is a classical model of colitis in the rat. Little is known about the time-related effect of TNBS on the contractility and morphology of the rat ileum. After 36 h, TNBS induced acute ileitis. Spontaneous activity of longitudinal muscle strips was decreased, as were receptor- and nonreceptor-mediated contractions and contractions induced by electrical stimulation. After 1 week, mucosal integrity was restored, although the thickness of both mucosal and muscle layers was increased. Spontaneous activity, receptor- and nonreceptor-mediated contractions and electrically induced contractions of longitudinal muscle strips were increased due to hypertrophy and hyperplasia of smooth muscle cells. This was confirmed in the contractility study of individual muscle cells. Functional alterations after 1 week were restricted to a decreased response to substance P. TNBS-ileitis in the rat lacks a chronic phase and is accompanied by functional hypocontractility of longitudinal smooth muscle cells during the acute inflammation, whereas the contractility of the longitudinal muscle layer is increased in the postinflammation phase due to structural alterations. There is a selective inhibition of the response to substance P in the postinflammation phase.

Selective enhancement of histamine H1‐receptor responses in guinea‐pig ileal smooth muscle by 1,4‐dithiothreitol

1,4-Dithiothreitol (DTT; 1 mM, 30 min preincubation) produced a small, non-specific potentiation of spasmogenic activity in longitudinal muscle strips of guinea-pig small intestine. A direct comparison of contractile responses elicited by histamine and a range of H1- and non-H1-receptor agonists indicated that DTT produced a significantly greater potentiation of H1-receptor responses. This apparently selective increase in tissue sensitivity to histamine H1-receptor agonists did not appear to be a consequence of the inhibition of histamine N-methyl transferase or diamine oxidase activity. Potentiation of the responses to histamine by DTT was still observed in the presence of SKF 91488 (10 microM) and aminoguanidine (1 microM). The potentiation elicited by DTT was readily reversed by the sulphydryl oxidizing agent dithiobis-(2-nitrobenzoic acid) (DTNB). This suggests that the mechanism of action of DTT involves the reduction of disulphide bonds. Exposure of ileal smooth muscle to DTT following desensitization with histamine (100 X EC50 [- DTT]) resulted in a 6.9 +/- 0.7 fold shift of the concentration-response curve to lower agonist concentrations. Conversely, following potentiation of the response to histamine with DTT, exposure of the tissue to desensitizing concentrations of histamine resulted in a dextral shift of the dose-response curve (dose ratio = 39.5 +/- 1.2) to higher agonist concentrations. The results of this study suggest that DTT may be a useful tool with which to investigate histamine H1-receptor mechanisms in ileal smooth muscle.

Nerve-mediated inhibition of mechanical activity in rabbit duodenum and the effects of desensitization to adenosine and several of its derivatives.

1. Inhibition of mechanical activity in longitudinal muscle strips of rabbit duodenum was induced by perivascular and intramural nerve stimulation.2. The effects of perivascular stimulation were abolished by phentolamine + propranolol, guanethidine, reserpine and by tetrodotoxin. The effects of intramural stimulation were abolished only by tetrodotoxin.3. Noradrenaline, phenylephrine, isoprenaline, adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and adenosine each produced an inhibition of mechanical activity. The relative potencies of these agonists were noradrenaline>isoprenaline>phenylephrine>ATP>ADP>adenosine>AMP.4. Exposure of tissues to high concentrations of either ATP or adenosine desensitized the tissue to further exposure to ATP, ADP, AMP and adenosine, whilst the inhibitory effects of noradrenaline, phenylephrine and isoprenaline and of perivascular and intramural stimulation were unaffected. The effects of desensitization were reversible.5. It was concluded that the effects of intramural stimulation were mediated neither by noradrenaline nor by adenosine or its derivatives.