Effects of YM905, a novel muscarinic M3-receptor antagonist, on experimental models of bowel dysfunction in vivo. (17/144)

We investigated the effects of YM905 [(+)-(1S,3'R)-quinuclidin-3'-yl 1-phenyl-1,2,3,4-tetrahydroisoquinoline-2-carboxylate monosuccinate], a new orally active muscarinic M3-receptor antagonist, on bowel dysfunction in vivo using experimental models that reproduce the symptoms present in irritable bowel syndrome (IBS). YM905 potently inhibited restraint stress-induced fecal pellet output in fed rats (ED50: 4.0 mg/kg) and diarrhea in fasted rats (ED50: 1.7 mg/kg), with similar potencies to the inhibition of bethanechol-, neostigmine- and nicotine-induced fecal pellet output in rats (ED50: 3.3, 7.9 and 4.5 mg/kg, respectively). YM905 also inhibited 5-hydroxytryptamine (5-HT)-, prostaglandin E2- and castor oil-induced secretory diarrhea in mice (ED50: 5.5, 14 and 6.3 mg/kg, respectively), but showed no significant effect on cholera toxin-induced intestinal secretion in mice. In addition, YM905 (3, 10 mg/kg) reversed morphine-decreased postprandial defecation in ferrets, a model of spastic constipation, whereas remosetron, a 5-HT3-receptor antagonist, was not effective. The mode of YM905 action was similar to that of darifenacin, a selective M3-receptor antagonist, with equivalent potencies. By contrast, propantheline, an antimuscarinic drug that has been used for IBS, was much less potent. These results show that YM905 ameliorates a wide spectrum of bowel dysfunctions through the blockade of M3 receptors, suggesting its therapeutic potential for treating IBS.  (+info)

Dependency of detrusor contractions on calcium sensitization and calcium entry through LOE-908-sensitive channels. (18/144)

1. The subcellular mechanisms regulating stimulus-contraction coupling in detrusor remain to be determined. We used Ca(2+)-free solutions, Ca(2+) channel blockers, cyclopiazonic acid (CPA), and RhoA kinase (ROK) inhibitors to test the hypothesis that Ca(2+) influx and Ca(2+) sensitization play primary roles. 2. In rabbit detrusor, peak bethanechol (BE)-induced force was inhibited 90% by incubation for 3 min in a Ca(2+)-free solution. By comparison, a 20 min incubation of rabbit femoral artery in a Ca(2+)-free solution reduced receptor-induced force by only 5%. 3. In detrusor, inhibition of sarcoplasmic reticular (SR) Ca(2+) release by 2APB, or depletion of SR Ca(2+) by CPA, inhibited BE-induced force by only 27%. The CPA-insensitive force was abolished by LaCl3. By comparison, 2APB inhibited receptor-induced force in rabbit femoral artery by 71%. 4. In the presence of the non-selective cation channel (NSCC) inhibitor, LOE-908, BE did not produce an increase in [Ca(2+)]i but did produce weak increases in myosin phosphorylation and force. 5. Inhibitors of ROK-induced Ca(2+) sensitization, HA-1077 and Y-27632, inhibited BE-induced force by approximately 50%, and in combination with LOE-908, nearly abolished force. 6. These data suggest that two principal muscarinic receptor-stimulated detrusor contractile mechanisms include NSCC activation, that elevates [Ca(2+)]i and ROK activation, that sensitizes cross bridges to Ca(2+).  (+info)

Cholinergic stimulation enhances colonic motor activity, transit, and sensation in humans. (19/144)

The cholinesterase inhibitor neostigmine indirectly stimulates muscarinic M(1)/M(2)/M(3) receptors, thereby reducing colonic distension in acute colonic pseudo-obstruction. We investigated the dose-response profile for the colonic sensorimotor effects of neostigmine and bethanechol, a direct muscarinic M(2)/M(3) agonist in humans. A barostat-manometric assembly recorded phasic pressures, tone, and pressure-volume relationships (compliance) in the descending colon and rectum of 30 healthy subjects who received intravenous neostigmine (0.25, 0.75, or 1.5 mg; n = 15) or subcutaneous bethanechol (2.5, 5, or 10 mg; n = 15). Sensation to luminal distension was also assessed. Thereafter, the effects of neostigmine and bethanechol on colonic transit (geometric center) were compared with those of saline by scintigraphy in 21 subjects. Both drugs increased colonic phasic pressure activity, reduced rectal compliance, and enhanced urgency during rectal distension. Neostigmine also reduced colonic and rectal balloon volumes, reflecting increased tone by an average of 12% and 25% for the highest dose, respectively. Only neostigmine reduced colonic compliance, accelerated colonic transit [mean geometric center at 90 min 2.5 vs. 1.0 (placebo)], and increased pain perception during colonic distension. We conclude that neostigmine has more prominent colonic motor and sensory effects than bethanechol. Moreover, neostigmine induces coordinated colonic propulsion, perhaps by stimulating muscarinic M(1) receptors in the myenteric plexus.  (+info)

Regional differences in the response of feline esophageal smooth muscle to stretch and cholinergic stimulation. (20/144)

There are no objective differences in neural elements that explain regional differences in neural influences along the smooth muscle (SM) esophageal body (EB). Regional differences in muscle properties are present in the lower esophageal sphincter (LES). This study examines whether regional differences in SM properties exist along the EB and are reflected in length-tension relationships and responses to cholinergic excitation. Circular SM strips from feline EB at 1 cm (EB1) and 3 cm (EB3) above LES and from clasp and sling muscle bundles of LES were assessed in normal and calcium-free solutions with and without bethanechol stimulation. Neural inhibition was assessed by electrical field stimulation (EFS). EB3 developed significantly higher tension in response to stretch and to bethanechol than did EB1. The relaxation response to EFS in bethanechol-precontracted strips was less in EB3 than in EB1. In LES, clasp developed higher resting tension than sling but less active tension in response to bethanechol. EFS-induced relaxations of sling and clasp tissues precontracted by bethanechol were not different. In calcium-free solution, length-tension differences between EB3 and EB1 persisted, but those of LES clasp and sling were abolished. Therefore, regional myogenic differences exist in feline EB circular SM as well as in LES and may contribute to the nature of esophageal contraction.  (+info)

Inhibition of pancreatic protein secretion by ghrelin in the rat. (21/144)

1. The role of ghrelin in the regulation of pancreatic protein secretion was investigated in vivo using anaesthetized rats with pancreatic ductal cannulas, and in isolated pancreatic acinar cells and pancreatic lobules in vitro. 2. In vivo, pancreatic protein output stimulated by CCK-8 (400 pmol kg(-1) h(-1)) was dose-dependently inhibited by continuous ghrelin infusion (1.2 and 12 nmol kg(-1) h(-1)) by 45 +/- 8 and 84 +/- 7 %, respectively. 3. In rats with acute subdiaphragmatic vagotomy, ghrelin (12 nmol kg(-1) h(-1)) significantly inhibited CCK-stimulated pancreatic protein secretion by 75 +/- 18 %. 4. Infusion of ghrelin (12 nmol kg(-1) h(-1)) abolished pancreatic protein secretion caused by the central vagal stimulant 2-deoxy-D-glucose (75 mg kg(-1)), whereas bethanechol-stimulated pancreatic protein output was inhibited by only 59 +/- 7 %. 5. In vitro, ghrelin (10(-11)-10(-7) M) produced no change in basal amylase release from dispersed, purified acinar cells. Co-incubation of ghrelin (10(-11)-10(-7) M) with CCK-8 (10(-10) M) demonstrated no inhibition of CCK-stimulated amylase release from dispersed acini. In contrast, ghrelin (10(-9)-10(-7) M) dose-dependently inhibited amylase release from pancreatic lobules exposed to 75 mM potassium. 6. Our results show that (1) ghrelin is a potent inhibitor of pancreatic exocrine secretion in anaesthetized rats in vivo and in pancreatic lobules in vitro; and (2) the actions of ghrelin are indirect and may be exerted at the level of intrapancreatic neurons.  (+info)

Involvement of potassium channels in spinal antinociceptions induced by fentanyl, clonidine and bethanechol in rats. (22/144)

In the central nervous systems, intracellular and extracellular movement of potassium ions plays an important role in regulating neuronal excitability and the release of neurotransmitters. The purpose of our study was to determine whether nicorandil (adenosine triphosphate-sensitive K+ channel opener) exerts antinociceptive effects by itself or in combination with fentanyl, clonidine and bethanechol and whether glibenclamide (adenosine triphosphate-sensitive K+ channel blocker) and charybdotoxin (Ca2+-activated K+ channel blocker) may antagonize the antinociceptive action of fentanyl, clonidine and bethanechol. Antinociceptive effects were assessed using the tail-flick test in rats. Nicorandil (100 microg) and antinociceptively ineffective doses of fentanyl (1 microg), clonidine (2.5 microg) or bethanechol (10,ug) were coadministered intrathecally (i.t.). Glibenclamide (100 microg) or charybdotoxin (2.5 ng) were administered i.t. at 5 min before each effective dose of fentanyl (2.5 microg), clonidine (10 microg) or bethanechol (40 microg). The present findings demonstrated that i.t. administration of nicorandil alone exerted no influence on the tail-flick latency. However, concomitant administrations of antinociceptively inactive doses of fentanyl, clonidine or bethanechol with nicorandil elicited significant suppression of the thermonociceptive response. Also, each antinociception induced by fentanyl, clonidine or bethanechol was partially antagonized by both glibenclamide and charybdotoxin. These findings showed that activation of the K+ channel might enhance the antinociceptive effects of fentanyl, clonidine and bethanechol.  (+info)

Muscarinic agonist-induced non-granular and granular secretion of amylase in the parotid gland of the anaesthetized rat. (23/144)

The muscarinic agonist bethanechol was infused intravenously, under alpha- and beta-adrenoceptor blockade, in anaesthetized rats at various dose levels (5-10, 20 and 40-50 microg kg(-1) min(-1)) over 30 min. The amount of saliva secreted from the parotid gland was dose dependent at 95, 202 and 737microl, respectively. The salivary amylase activity was approximately the same at the two lower doses (506 U and 448 U, respectively), while it was higher (1268 U) at the highest dose. In response to the highest dose, but not to the lower doses, the total parotid glandular amylase activity and the numerical density of parotid acinar secretory granules were lowered, by 25 % and 22 %, respectively. Thus, in the rat parotid gland, agonists such as bethanechol, which use Ca(2+) as a second messenger, may release proteins not only by non-granular mechanisms but also, and in contrast to the general belief, by granule exocytosis.  (+info)

Generation of a cell line with smooth muscle phenotype from hypertrophied urinary bladder. (24/144)

We have established a cell line from hypertrophied rabbit urinary bladder smooth muscle (SM) that stably expresses SM myosin (SMM). These cells, termed BSM, are spindle shaped and form swirls, similar to the "hills and valleys" described for cultured aortic SM cells. Western blotting revealed that BSM expresses the amino-terminal SMM heavy chain isoform SM-B, the carboxy-terminal SM1 and SM2 isoforms, and SM alpha-actin. In addition, they express cGMP-dependent protein kinase G, made by contractile SM cells in vitro but not by noncontractile cells synthesizing extracellular matrix. Immunofluorescence studies indicate a homogeneous population of cells expressing alpha-actin and SMM, including the SM-B isoform, and karyotyping demonstrates a stable 4N chromosomal pattern. These cells also express calcium-dependent myosin light chain kinase and phosphatase activity and contract in response to the muscarinic agonist bethanechol. To our knowledge, BSM is the first visceral SM cell line that expresses the SM-B isoform and might serve as a useful model to study the transcriptional regulation of tissue-specific SMM isoforms in differentiation and pathological SM.  (+info)