Contractions Of Longitudinal Muscle Strips Research Articles

CCK mediated the inhibitory effect of oxytocin on the contraction of longitudinal muscle strips of duodenum in male rats

The aim of the present study was to investigate the effect of oxytocin (OT) on duodenum motility in rats and the possibility that cholecystokinin (CCK) was involved in this process. The isometric contraction of longitudinal muscle strips of duodenum was monitored by polygraph. ELISA was used to measure the concentration of CCK and OT in duodenum. CCK mRNA was assayed by RT-PCR. Oxytocin receptor (OTR) and CCK in duodenum were located by immunohistochemistry and immunofluorescence staining. OT (10⁻⁵ and 10⁻⁶ M) inhibited the spontaneous contraction of the muscle strips. On the contrary, atosiban (OT receptor antagonist), lorglumide (CCK₁ receptor antagonist), and tetrodotoxin (TTX, blocker of voltage-dependent Na(+) channel on nerve fiber) excited the contraction. The inhibitory effect of OT on duodenal motility was reversed by pretreatment of atosiban, lorglumide, or TTX. Exogenous OT did not influence the expression of OT mRNA in duodenum but increased the concentration of CCK in the culture medium of the cells isolated from longitudinal muscle myenteric plexus. The OTR and CCK were co-expressed in the neurons of the myenteric plexus in duodenum. We concluded that OT inhibited the contraction of the LD spontaneous contraction of rats in vitro. This effect was mediated by the CCK released from the neurons of the myenteric plexus in duodenum.

Ethanol Upregulates iNOS Expression in Colon Through Activation of Nuclear Factor-kappa B in Rats

Alcohol inhibits colonic motility but the mechanism is unknown. The goal of this study was to test the possibility that nuclear factor-kappa B (NF-kappaB) is involved in the upregulation of inducible nitric oxide synthase (iNOS) expression induced by ethanol in colon. The isometric contraction of longitudinal muscle strips of proximal colon (LP) was monitored by polygraph. Western blot analysis was used to measure the amount of iNOS and I-kappaB in the cytoplasm and P65 in the nucleus. Immunohistochemistry was applied to locate iNOS in colon. Ethanol (87mM) inhibited the contraction of LP. Pretreatment of S-methylisothioure (SMT) (1 mM), a specific iNOS inhibitor, Pyrrolidine dithiocarbamate (PDTC) (10 mM) and BAY11-7082(10 mM), specific inhibitors of NF-kappaB significantly reversed the inhibitory effect of ethanol on LP contraction. Ethanol increased the amount of iNOS and content of NO in colon, and these effects were attenuated by pretreatment of PDTC. Following ethanol administration, the amount of I-kappaB in the cytoplasm decreased, but that of P65, the subunit of NF-kappaB in the nucleus, increased. The iNOS was located in the cell body of myenteric plexus in colon. Ethanol inhibited the contraction of LP in colon mainly through activation of NF-kappaB, the subsequent upregulation of iNOS expression and increase of NO release in myenteric plexus.

Endothelin ET A but not ET B receptors mediate contraction of common bile duct

Endothelin (ET) causes contraction of the gallbladder. To investigate effects of ET in the common bile duct, we measured contraction of longitudinal muscle strips from guinea pig common bile ducts induced by ET-related peptides and binding of 125I-ET-1 to cell membranes prepared from the common bile duct. Visualization of 125I-ET-1 binding sites in tissue was performed by autoradiography. ET-1 caused tetrodotoxin and atropine-insensitive contraction. In terms of maximal tension of contraction, ET-1, ET-2 and ET-3 were equal in efficacy. However, sarafotoxin S6c, a selective ET B receptor agonist, caused only a negligible contraction. The relative potencies for ET isopeptides to cause contraction were ET-1=ET-2>ET-3. The ET-1-induced contraction was inhibited by BQ-123, an ET A-receptor-selective antagonist, but not by BQ-788, an ET B-receptor-selective antagonist. In addition, the combination of both antagonists, BQ-123 and BQ-788, inhibited ET-1 induced contraction but did not potentiate the inhibition caused by BQ-123 alone. These indicate that ET A but not ET B receptors mediate the contraction. Autoradiography localized 125I-ET-1 binding to the smooth muscle layer. Binding of 125I-ET-1 to the smooth muscle cell membranes was saturable and specific. Analysis of dose–inhibition curves indicated the presence of ET A and ET B receptors. These results demonstrate that ET causes contraction of longitudinal muscle of the common bile duct. Different from the gallbladder, which possesses both ET A and ET B receptors cooperating to mediate muscle contraction, the common bile duct possesses two classes of ET receptors, but only the ET A receptor mediates the contraction.

Potentiation of motilin-induced contraction by nitric oxide synthase inhibition in the isolated chicken gastrointestinal tract.

The present experiments were designed to determine whether or not endogenous nitric oxide (NO) modifies the contractile response to chicken motilin (ch-MT) in the gastrointestinal (GI) tract (proventriculus and small intestine) of the chicken. ch-MT (1 nmol L(-1)-1 micromol L(-1)) caused contractions of longitudinal muscle strips of the proventriculus through both myogenic and neurogenic (mostly cholinergic) mechanisms. On the other hand, ch-MT (0.1 nmol L(-1)-100 nmol L(-1)) contracted the small intestine (duodenum, jejunum and ileum) only through a myogenic mechanism. L-Nitroarginine methylester (L-NAME) potentiated, and L-arginine inhibited, the ch-MT- induced contraction without affecting the responsiveness of acetylcholine (ACh) or 5-hydroxytryptamine in the proventriculus. Electrical field stimulation (EFS)- and 1,1-dimethyl-4-phenylpiperazinium (DMPP)- induced contractions were also potentiated by L-NAME. The potentiation by L-NAME was prevented by L-arginine but not by D-arginine. However, in the presence of atropine or tetrodotoxin, neither L-NAME nor L-arginine modified the responses to ch-MT and DMPP. In contrast to the proventriculus, L-NAME and L-arginine were both ineffective in modifying the ch-MT-induced contraction in the small intestine. These results indicate that NO synthase inhibition potentiates the contractile response of ch-MT, EFS and DMPP in the chicken proventriculus through reduction of endogenous NO-mediated presynaptic inhibition on neural ACh release. However, NOS inhibition did not modify the myogenic (direct) action of ch-MT in gastric and intestinal smooth muscles of the chicken.

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.

Functional evidence for a 5-HT2B receptor mediating contraction of longitudinal muscle in human small intestine.

Application of 5-hydroxytryptamine induces contraction of longitudinal muscle strips from human terminal ileum. The response was resistant to antagonism by ketanserin, ondansetron or DAU6285, but was non-surmountably antagonized by methysergide. The selective 5-HT2B/2C receptor antagonist, SB 200646A evoked a concentration-dependent, parallel and dextral displacement of the concentration-response curve to 5-HT, yielding a pA2 estimate of 7.17. Application of yohimbine, a 5-HT1 and 5-HT2B receptor antagonist, also induced a rightward shift of the response curve to 5-HT, yielding a pA2 estimate of 8.10. In conclusion, it appears that a 5-HT2B receptor mediates the contractile response of the longitudinal muscle of human small intestine to 5-HT.

Monoamines and neuropeptides as transmitters in the sedentary polychaete Sabellastarte magnifica: actions on the longitudinal muscle of the body wall.

Pharmacological studies on the body wall musculature of the sedentary polychaete Sabellastarte magnifica show a potential neurotransmitter role for monoamines and neuropeptides in this organism. All catecholamines induced contraction of longitudinal muscle strips, while serotonin and the neuropeptides FMRFamide and substance P caused a relaxation of both resting and active muscle. In addition, we demonstrate catecholaminergic and serotonergic pathways in the nervous system of this sabellid, using immunohistochemistry and catecholamine-induced fluorescence. The presence of neuropeptide-containing fibers in the nervous system of this polychaete has been previously reported. Together these results suggest that catecholamines act as excitatory transmitters on the longitudinal muscle cells of the body wall of S. magnifica, while serotonin and FMRFamide, and possible substance P, are inhibitory transmitters. The possibility of coexistence of serotonin and FMRFamide within the same neuronal cell bodies and fibers of this polychaete is also explored.

Characterization of neuronal cholecystokinin receptor by L-364,718 in Auerbach's plexus

The release of [ 3H]acetylcholine ([ 3H]ACh) from Auerbach's plexus and the contraction of longitudinal muscle strips in response to the administration of cholecystokinin (CCK) were measured and recorded simultaneously. The peripheral CCK receptor antagonist, 3S(−)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepine-3-yl)-1Hindole-2-carboxamide (L-364,718), antagonized the ACh releasing effect of CCK in a dose-dependent manner. The IC 50 value and the dissociation constant (K D) were 41.0 ± 2.0 pM and 0.06 ± 0.01 nM, respectively. These results suggest that L-364,718 is a very potent antagonist of the neuronal CCK receptors.

The role of intracellular calcium stores in motilin induced contractions of the longitudinal muscle of the rabbit duodenum

The contraction of longitudinal muscle strips of the rabbit duodenum in response to motilin and acetylcholine was investigated in normal and high K+-solutions in the presence and absence of external calcium, in order to demonstrate the existence of pharmaco-mechanical coupling for motilin and to examine whether the peptide mobilizes calcium from an intracellular store. In depolarized smooth muscle (140 mM K+), motilin (3.2 x 10(-9)-1 x 10(-7) M) and acetylcholine (1 x 10(-5) M) were still capable of causing a considerable, transient, concentration-dependent contraction in the presence of Ca2+. The 'extra'-contraction to motilin was not blocked by tetrodotoxin (1 microgram/ml) nor by atropine (10(-7) M), but acetylcholine (10(-5) M) was blocked by atropine. Verapamil (10(-7) M) could selectively block the K+ contraction without affecting the extra agonist contraction. Nitroprusside was ineffective up to 10(-4) M in high K+-solutions, but in normal Hepes-buffer it caused a concentration-dependent rightward shift of the concentration-response curve of motilin and acetylcholine contractions. In a calcium-depleted medium, high K+-depolarized muscle strips were still responsive to motilin and acetylcholine, but higher concentrations (10(-6) M) were needed than in the presence of calcium and the contractions reached only 57 +/- 11% and 74 +/- 9% respectively of the maximal contraction in 1.2 mM Ca2+ containing solutions. The response to motilin (10(-6) M) was not only smaller than that to acetylcholine (10(-5) M), it also faded more rapidly with time.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for neurokinin-3 receptor-mediated tachykinin release in the guinea-pig ileum

Contraction of longitudinal muscle strips of the guinea-pig ileum induced by the selective NK3 receptor agonist, succ-[Asp 6,MePhe 8]SP-(6-11) (senktide), were completely inhibited by tetrodotoxin and partially blocked by atropine. The atropine-resistant contraction was markedly reduced if the smooth muscle tachykinin receptors were either desensitized with the selective NK1 agonist substance P methyl ester, or blocked with the tachykinin receptor antagonist [D-Pro 4,D-Trp 7,9,10]SP-(4-11). These results suggest that activation of NK3 receptors on enteric neurones results in acetylcholine and tachykinin release.