Regional Comparison of Rat Colon Mechanics

The purpose of this study was to examine the force-velocity characteristics of colonie muscle and to determine whether these factors contribute to regional specialization of the colon observed in adult Fischer rats. Four measurements were obtained from circular colon muscle strips: maximum shortening velocity, a reflection of crossbridge cycling rate; extension of the parallel elastic component, a measure of passive muscle properties of relaxed muscle; the series elastic component, a measure of passive muscle properties of contracted muscle; and peak isometric force, which is equal to the product of the number of activated crossbridges and the strength of individual crossbridges. Muscle length (L) was expressed in terms of the length of optimal tension development (L_o). Peak isometric force and maximum shortening velocity were 848.9 ± 114.7 g/cm² and 0.082 ± 0.012 L_o/s for muscle strips from the proximal colon, and 948.0 ± 138.2 g/cm² and 0.083 ± 0.014 L_o/s for muscle strips from the distal colon. Shortening velocity, isometric force, and load extension properties of the parallel elastic component and the series elastic component are similar in proximal and distal rat colon. This suggests that regional specialization is not determined at the myofibril level but is most likely determined by extrinsic regulatory factors at the neural or receptor level.     

Regulation of smooth muscle excitation and contraction

Abstract  Smooth muscle cells (SMC) make up the muscular portion of the gastrointestinal (GI) tract from the distal oesophagus to the internal anal sphincter. Coordinated contractions of these cells produce the motor patterns of GI motility. Considerable progress was made during the last 20 years to understand the basic mechanisms controlling excitation-contraction (E-C) coupling. The smooth muscle motor is now understood in great molecular detail, and much has been learned about the mechanisms that deliver and recover Ca²⁺ during contractions. The majority of Ca²⁺ that initiates contractions comes from the external solution and is supplied by voltage-dependent Ca²⁺ channels (VDCC). VDCC are regulated largely by the effects of K⁺ and non-selective cation conductances (NSCC) on cell membrane potential and excitability. Ca²⁺ entry is supplemented by release of Ca²⁺ from IP₃ receptor-operated stores and by mechanisms that alter the sensitivity of the contractile apparatus to changes in cytoplasmic Ca²⁺. Molecular studies of the regulation of smooth muscle have been complicated by the plasticity of SMC and difficulties in culturing these cells without dramatic phenotypic changes. Major questions remain to be resolved regarding the details of E-C coupling in human GI smooth muscles. New discoveries regarding molecular expression that give GI smooth muscle their unique properties, the phenotypic changes that occur in SMC in GI motor disorders, tissue engineering approaches to repair or replace defective muscular regions, and molecular manipulations of GI smooth muscles in animals models and in cell culture will be topics for exciting investigations in the future.     

Response of Smooth Muscle from Proximal and Distal Human Colon

Regional differences in colonic motility may be responsible for the orderly transit of intraluminal contents through the colon. The aims of this study were to compare the effect of stretch on active and passive stress development in colonic muscle from the proximal and distal colon and to compare the responses of these tissues to KC1 or bethanechol stimulation. Strips of taenia or circular smooth muscle were obtained from the disease-free segment of the colon removed for adenocarcinoma. Passive, active, and total isometric stress were measured on full-thickness strips of circular or longitudinal taenial muscle stimulated with bethanechol (10⁻⁴ M) as the muscles were stretched to 120% of the length of optimum tension ( L _o.) The tissues then were stimulated with increasing concentrations of KCI and bethanechol while being stretched at L _o. The active stress in the proximal circular muscle was greater at all levels of stretch than in distal circular or longitudinal muscle ( p <.001). The resting and passive stress were greater in distal circular and longitudinal taenial muscle than in proximal circular muscle ( p < .05). There was a dose-dependent increase in stress development to bethanechol and KCl in each type of muscle. Proximal circular muscle had the greatest response. The EDSO was shifted to the right in distal circular muscle (2.6 ± 0.1 × 10⁻⁵ M) compared to proximal circular muscle (1.1 ± 0.1 × 10⁻⁵ M) ( p < .001). These studies suggest that muscle stress differs in different locations of the colon and the role of active and passive stress development must be considered in models explaining in vivo colonic motility disturbances.     

Effect of chronic Li+ treatment on free intracellular Mg2+ in human neuroblastoma SH-SY5Y cells

Objectives:  Previous findings have demonstrated Li⁺/Mg²⁺ competition at therapeutic intracellular Li⁺ levels after acute Li⁺ treatment in human neuroblastoma SH-SY5Y cells. In the current study, we examined whether Li⁺/Mg²⁺ competition exists at therapeutically relevant extra- and intracellular [Li⁺] after chronic Li⁺ loading times.
Methods:  In human neuroblastoma cells, intracellular free Mg²⁺ was determined by fluorescence spectroscopy with the fluorophore furaptra. Intracellular Li⁺ and Mg²⁺ were measured by atomic absorption spectrophotometry.
Results:  After loading of the neuroblastoma cells with 1–2 mM extracellular Li⁺ for 24–72 h, the observed, increased intracellular free [Mg²⁺] levels were significantly higher (p < 0.03) than those in matched Li⁺ free cells, and intracellular [Li⁺] was found to be at therapeutic intracellular levels (0.7–1.5 mM).
Conclusions:  The results demonstrate that Li⁺/Mg²⁺ competition exists after chronic treatment with Li⁺ at therapeutically relevant intracellular Li⁺ levels in neuroblastoma cells. We found differences between acute and chronic Li⁺ treatment effects on the extent of Li⁺/Mg²⁺ competition. Possible reasons for these differences are discussed.     

Rat Colonic Motor Responses to Inflammatory Mediators In Vitro: A Poor Model for the Human Colon

There is evidence that the rat colon exposed to trinitrobenzenesulfonic acid (TNBS) develops a colitis-like inflammation which may be a model for inflammatory bowel disease (IBD) in humans. The aim of this study was to determine if the pharmacologic responses of the normal rat distal colon to several IBD-associated inflammatory mediators were sufficiently similar to those of the normal human colon for the rat with TNBS-induced colitis to provide an appropriate model for their effects on human colonic motility in IBD. Longitudinal and circular muscle mechanical properties were also investigated. Longitudinal muscle responded with concentration-dependent contractions to histamine, leukotriene D₄, and prostaglandins E₂ and F-₂α, which were mediated by a direct action. In general, circular muscle responses to these mediators were smaller, and in the cases of leukotriene D₄ and prostaglandin F₂α, these were modulated by the concurrent activation of intrinsic inhibitory neurons. The mechanical properties of rat distal colonic longitudinal and circular muscle differed significantly from the equivalent human muscles. In most aspects studied normal rat distal colonic smooth muscles were at variance with previously reported properties of the equivalent human muscles. Thus the rat colon would be inappropriate as a model to study potential inflammatory mediator-induced alterations of colonic motility in IBD.     

The role of Ca2+ in the elimination of polyneuronal innervation of rat soleus muscle fibres

The mechanism by which nerve - muscle contacts are reduced during postnatal development of the rat soleus muscle was investigated using electrophysiological methods. Between days 7 and 9 after birth, soleus muscle fibres lose 0.19–0.24 terminals per muscle fibre within 24 h. A much more rapid loss of contacts is seen when muscles are exposed in vitro to acetylcholine (10⁻³ g/ml). In this case 0.67–0.87 terminals per muscle fibre lose contact within 2 h. The loss of neuromuscular contacts induced by acetylcholine can be reduced by preincubating the muscles in solutions containing acetoxymethyl ester of 1,2-bis(2-amino-phenoxylethane-N,N₁;N₁-tetraacetic acid (BAPTA-AM), a Ca²⁺ chelating agent that enters cells and reduces the Ca²⁺ transients inside the cell. Treatment of muscles with nifedipine, which blocks dihydropyridine-sensitive (L-type) Ca²⁺ channels, also reduced the acetylcholinesterase-induced loss of neuromuscular contacts. The results indicate that transient increases in Ca²⁺ inside nerve terminals contribute to loss of neuromuscular contacts, and that these increases occur by Ca²⁺ entry through L-type channels.     

Oxcarbazepine: Mechanisms of Action

Summary: The antiepileptic drug (AED) oxcarbazepine (OCBZ) and its rapidly formed 10-monohydroxy metabolite (MHD) protect against electroshock-induced tonic hindlimb extension in rodents (ED₅₀ 14–21 mg/kg p.o.). Both stereoisomers of MHD also protect. As with carbamazepine (CBZ), these findings suggest clinical efficacy against generalized tonic-clonic and, to some extent, partial seizures. OCBZ (IC₅₀ 5 × 10⁸ M ), MHD (IC₅₀ 2 × 10^-8 M ) and CBZ (IC₅₀ 6 × 10^-7 M ) limit the frequency of firing of sodium-dependent action potentials by cultured mouse central neurons and reduce V _mix progressively in a use-dependent manner at concentrations below therapeutic plasma concentrations in OCBZ-treated patients. This suggests that blockade of voltagesensitive sodium channels could contribute to the antiepileptic efficacy of OCBZ. Blockade of penicillin-induced epileptiform discharges in hippocampal slices by MHD and its stereoisomers was diminished when the potassium channel blocker 4-aminopyridine was added to the bath fluid. This indicates that additional mechanisms of action, e.g., an effect on potassium channels, might be clinically important. In addition, both stereoisomers are equally responsible for the antiepileptic activity of the racemate, i.e., MHD, and are therefore likely to play a therapeutic role. Such actions could confer broad clinical utility on OCBZ.     

Neuropeptide Y Inhibits the Migrating Myoelectric Complex and Delays Small Intestinal Transit in Rats

The effect of neuropeptide Y (NPY) on myoelectric activity of the small intestine was related to transit of a radioactive marker in fasted conscious rats. Myoelectric activity was recorded with bipolar electrodes implanted 5, 20, and 35 em distal to pylorus. A radioactive marker was administered luminally in the duodenum immediately after an activity front of a migrating myoelectric complex (MMC) had passed the first recording site. Intravenous infusion of NPY (50–100 pmol kg⁻¹ min ⁻¹) did not affect the MMC in the duodenum but interrupted its distal propagation and inhibited spiking in the jejunum. At higher doses, NPY (200–800 pmol kg⁻¹ min⁻¹) abolished the MMC at all recording sites. Effects of NPY on myoelectric activity were not prevented by guanethidine, phentolamine, propranolol, or naloxone. The effects of NPY on myoelectric activity corresponded to a dose-related slowing of transit of the marker. In controls, the peak of the marker was propagated ahead of the activity front over the three recording sites. NPY (100 pmol kg⁻¹ min⁻¹) slowed transit, with the peak of the marker proximal to the third electrode site. NPY (400 pmol kg⁻¹ min⁻¹) further delayed transit, with the peak of the marker proximal to the second electrode site. We conclude that the activity front of the MMC exerts a high propulsive capacity. NPY produced a dose-related nonadrenergic inhibition of the intestinal myoelectric activity, which may account for a delayed transit of intestinal contents.     

Safety and efficacy of botulinum toxin type A following long-term use

Botulinum toxin serotype A (BoNT-A) has long heritage of use leading to confidence in its safety and efficacy. The application of BoNT-A does not lead to persistent histological changes in the nerve terminal or the target muscle. Clinical trials defined the safety and tolerability profile of BoNT-A across common therapeutic indications and showed an incidence of adverse events of approximately 25% in the BoNT-A-treated group compared with 15% in the control group. Focal weakness was the only adverse event to occur more often following BoNT-A treatment. Long-term BoNT-A administration has been assessed in various treatment settings, with the level and duration of BoNT-A efficacy response being maintained over repeated rounds of injection with no major safety concerns. The treatment of children with cerebral palsy often require long-term, repeated, multimuscle BoNT-A injections that lead to the administration of comparably higher toxin doses. Despite the high total body doses used, their distribution over multiple muscles and injection sites means that systemic side effects are rare. Recent formulation changes have reduced the incidence of antibody development following treatment with BOTOX^®. These findings show long-term BoNT-A treatment to be both safe and efficacious for a wide variety of indications.     

Peripheral And Central Conduction Abnormalities In Diabetes Mellitus

Recently, chronic inflammatory cell responses including the upregulation of soluble adhesion molecules have been focused as a pathogenesis of chronic diabetic complications. However the response associated with acute Wallerian degeneration (WD) in diabetic nerve has not been evaluated. In this study, we investigated the pathological profiles of acute inflammation and its role in the development of WD in axotomized sciatic nerves in both control and streptozotocin induced diabetic rats. Activated macrophages were observed in the epineurial and the endoneurial area in both control (C) and diabetes (D) at 3 and 14 days after axotomy. However, the density of macrophages in diabetes was significantly reduced in the endoneurial area (3 days: C 74 ± 8/mm² vs. D 28 ± 12/mm², Mean ± SD, P < 0.01). CD8⁺ lymphocytes were rich in migration on the epineurial area at 3 days after axotomy in control. In contrast, density of CD8⁺ cell was significantly reduced in diabetes (C 132 ± 19/mm² vs. D 75 ± 8/mm², P < 0.005). At 14 days after axotomy, numerous lymphocytes filtrated in the endoneurial area in distal transected stump in control, although the epineurial CD8⁺ cell accumulation has already diminished. In diabetes, on the other hand, endoneurial lymphocytes were significantly fewer (D 31 ± 8/mm² vs. C 82 ± 16/mm², P < 0.001). On the pathological evaluation, a progress of nerve fiber degeneration was suppressed in diabetes. Our results suggested that the inflammatory response during acute WD is reduced in experimental diabetes, which might be a reason for delayed WD in diabetic nerve.     

Effects of Neurotensin on Gastric Smooth Muscle of Dog and Guinea Pig

Mechanical activity was recorded in muscle preparations isolated from different regions of dog and guinea pig stomach. Neurotensin (10⁻¹¹ to 10⁻⁸ mol/liter) produced three types of responses in canine gastric muscle: a small activation of tone infundic strips and in longitudinal strips from corpus and antrum; a transient inhibition of the rhythmic activity in circular strips from corpus, antrum, and outer pylorus; and a strong activation in the strips from inner pylorus. In guinea pig gastric muscle strong tonic responses were observed in circular fundic muscle strips, whereas in all other preparations the responses were negligible. All these effects were insensitive to atropine, dimethpyrindene, and tetrodotoxin. The neurotensin effect on strips from guinea pig stomach was strongly reduced in the presence of indomethacin or cortisone and markedly potentiated in the presence of arachidonic acid or prostaglandin F₂α. contrast, the excitatory effect of neurotensin on canine inner pylorus was potentiated during indomethacin treatment.     

Effects of gastrin-releasing peptide (GRP) on the mechanical activity of the human ileocaecal region in vitro

Mechanical activity was recorded in muscle preparations isolated from the human ileocaecal region. Gastrin-releasing peptide (GRP, 10⁻⁹− 10⁻⁷ mol L⁻¹) produced two types of response in the different muscle layers. Longitudinally cut strips showed a concentration-dependent increase in the rhythmic activity, whereas the circularly orientated layers generally reacted with a small decrease in tone. These effects could not be influenced by blockade of adrenergic or cholinergic receptors or nerve blockade with tetrodotoxin (TTX). Application of pentagastrin did not mimic the action of GRP. These findings suggest a direct action of GRP on smooth muscle via distinct receptors which have already been demonstrated to exist in human gastrointestinal tract. The opposite effects on circular and longitudinal strips might indicate a modulatory role of GRP in the control of ileocolonic transit.     

Diffusion,spread, and migration of botulinum toxin

Botulinum toxin (BoNT) is an acetylcholine release inhibitor and a neuromuscular blocking agent used for the treatment of a variety of neurologic and medical conditions. The efficacy and safety of BoNT depends on accurate selection and identification of intended targets but also may be determined by other factors, including physical spread of the molecule from the injection site, passive diffusion, and migration to distal sites via axonal or hematogenous transport. The passive kinetic dispersion of the toxin away from the injection site in a gradient‐dependent manner may also play a role in toxin spread. In addition to unique properties of the various BoNT products, volume and dilution may also influence local and systemic distribution of BoNT. Most of the local and remote complications of BoNT injections are thought to be due to unwanted spread or diffusion of the toxin's biologic activity into adjacent and distal muscles. Despite widespread therapeutic and cosmetic use of BoNT over more than three decades, there is a remarkable paucity of published data on the mechanisms of distribution and its effects on clinical outcomes. The primary aim of this article is to critically review the available experimental and clinical literature and place it in the practical context. © 2013 International Parkinson and Movement Disorder Society     

Ca2+ Channel Expression in the Oligodendrocyte Lineage

The development of oligodendrocytes from their precursor cells through different developmental stages can be studied in vitro. These stages can be distinguished by specific monoclonal antibodies and by a characteristic K⁺ channel profile. In this study we demonstrate that the occurrence of Ca²⁺ currents also undergoes marked changes during the development of mouse oligodendrocytes. Immature precursor cells which can develop into astrocytes or oligodendrocytes expressed two different types of voltage-activated Ca²⁺ channels. The expression of Ca²⁺ channels in precursor cells was strongly correlated with the expression of Na⁺ channels. When cells started to express the O1 antigen and were committed to the oligodendrocyte lineage, Ca²⁺ and Na⁺ currents could no longer be detected. Large Ca²⁺ currents were, however, recorded later in the development of the oligodendrocytes, correlated with the expression of the O10 antigen. The Ca²⁺ channels were classified as high and low voltage-activated Ca²⁺ channels according to their range of activation, and are further described by their kinetic and pharmacological properties.     

IGF-I promotes neuronal migration and positioning in the olfactory bulb and the exit of neuroblasts from the subventricular zone

While insulin-like growth factor-I (IGF-I) supports neuronal and glial differentiation in the CNS, it is largely unknown whether IGF-I also influences neuronal migration and positioning. We show here that the pattern of olfactory bulb (OB) layering is altered in Igf-I ^−/− mice. In these animals, Tbr1⁺-glutamatergic neurons are misplaced in the mitral cell layer (ML) and the external plexiform layer (EPL). In addition, there are fewer interneurons in the glomerular layer and the EPL of the Igf-I ^−/− mice, and fewer newborn neurons are incorporated into the OB from the forebrain subventricular zone (SVZ). Indeed, neuroblasts accumulate in the postnatal/adult SVZ of Igf-I ^−/− mice. Significantly, the positioning of Tbr1⁺-cells in a primitive ML is stimulated by IGF-I in cultured embryonic OB slices, an effect that is partially repressed by the phosphoinositide 3-kinase (PI3K) inhibitor. In OB cell cultures, IGF-I increases the phosphorylation of disabled1 (P-Dab1), an adaptor protein that is a target of Src family kinases (SFK) in the reelin signalling pathway, whereas reduced P-Dab1 levels were found in Igf-I ^−/− mice. Neuroblast migration from the rostral migratory stream (RMS) explants of postnatal Igf-I ^−/− was similar to that from Igf-I ^+/+ explants. However, cell migration was significantly enhanced by IGF-I added to the explants, an effect that was repressed by PI3K and SFK inhibitors. These findings suggest that IGF-I promotes neuronal positioning in the OB and support a role for IGF-I in stimulating neuroblast exit from the SVZ into the RMS, thereby promoting the incorporation of newly formed neurons into the OB.     

Cladribine impedes in vitro migration of mononuclear cells: a possible implication for treating multiple sclerosis

Background:  Damage of the blood–brain barrier and the migration of immunocompetent cells into the CNS represent key events in the immunopathogenesis of multiple sclerosis (MS). Cladribine is an immunosuppressive drug currently investigated in a phase-III clinical trial for relapsing–remitting MS. However, its precise mode of action remains elusive so far.
Methods:  Peripheral blood mononuclear cells (PBMCs) were isolated from five patients with MS and five healthy donors. PBMCs were treated with cladribine in vitro . The migratory capacity was studied in an in vitro Boyden chamber assay; cells and their rate of migration were analyzed by light microscopy and flow cytometry.
Results:  Cladribine decreased the migratory capacity of CD14⁺ monocytes, as well as of CD4⁺ and CD8⁺ T lymphocytes. T lymphocytes were affected more than monocytes. There was no difference in this effect when comparing mononuclear cells from MS patients with cells from healthy controls.
Conclusions:  Cladribine might achieve, at least in part, its clinical and paraclinical efficacy by inhibiting the migration of inflammatory cells into and within the CNS.     

Pericranial injection of botulinum toxin type A (Dysport®) for tension-type headache – A multicentre, double-blind, randomized, placebo-controlled study

Increasingly, botulinum type A toxin is used to influence pathologically increased muscle activity in conditions such as dystonia and spasticity. Studies have also assessed its efficacy in tension-type headache, where muscle tenderness may be increased. We undertook a prospective, multicentre, randomized, double-blind, placebo-controlled trial. Patients received injections of Dysport^® (total dose of 420 or 210 units) or saline placebo in 18 sites on the head and neck. Of 125 patients treated, 118 were included in the intention-to-treat dataset. No significant differences between each verum group and placebo were seen for the primary efficacy parameter – change in the number of headache-free days at 4–8 weeks after injection compared with 4 weeks before injection. The groups receiving 420 or 210 units of Dysport experienced 2.60 and 2.87 more headache-free days respectively, compared with 1.93 more headache-free days for the placebo group ( P  = 0.66 versus 420 units; P  = 0.52 versus 210 units). Treatment with 420 units of Dysport was associated with significant improvements compared with placebo for two secondary efficacy parameters: mean change in headache duration from baseline to weeks 8–12 ( P  < 0.05) and improved global physician and patient assessment scores ( P  < 0.05). Further studies should address the possible value of multiple injections with extended observation periods, dose optimization, and whether duration of headache history and number of previous treatments are predictors of patient response.     

Mitosis of Schwann Cells and Demyelination are Induced by the Amyloid Precursor Protein and Other Protease Inhibitors in the Rat Sciatic Nerve

We studied the cytological alterations produced in the rat sciatic nerve by the amyloid precursor protein (APP) containing the Kunitz insert (APP K⁺) and other protease inhibitors. Conditioning of nerve segments with APP K⁺, aprotinin or leupeptin for 5 days or more resulted in mitosis of Schwann cells, demyelination of fibres, and a <10-fold increase in Schwann cells, associated with demyelinated fibres. Altered fibres nevertheless involved a small part of the population. Nerve segments proximal and distal to the conditioned region showed almost no alteration. Conditioning with saline, heated APP K⁺, or APP without the Kunitz insert was not effective. We conclude that APP K⁺ and other protease inhibitors induce Schwann cells to enter the cell cycle, and once committed to proliferate they resorb their myelin. These functional properties of APP may be relevant to the pathogenesis of Alzheimer's disease.     

Expression of mutant ubiquitin (UBB+1) and p62 in myotilinopathies and desminopathies

Protein aggregates in muscle cells are the morphological hallmark of myofibrillar myopathies, including myotilinopathies and desminopathies. The aim of the present study is to analyse the expression of mutant ubiquitin (UBB⁺¹), an aberrant form of ubiquitin which accumulates in certain disorders characterized by intracellular aggregates of proteins, and p62, a multimeric signal protein which plays an active role in aggregate formation, in muscle biopsies from patients suffering from myotilinopathy and desminopathy in order to gain understanding of the mechanisms leading to protein aggregation in these disorders. Single immunohistochemistry, and single- and double-labelling immunofluorescence and confocal microscopy for UBB⁺¹ and p62, has been performed in muscle biopsies from patients suffering from myotilinopathy and desminopathy. Strong UBB⁺¹ immunoreactivity, colocalizing with myotilin aggregates, was found in muscle fibres in myotilinopathies. UBB⁺¹ accumulation, colocalizing with desmin aggregates, also occurs in desminopathies. In addition, strong p62 immunoreactivity colocalizing with myotilin aggregates was observed in myotilinopathies. Similarly, p62 immunoreactivity colocalizing with desmin aggregates was found in desminopathies. The present findings suggest that accumulation of protein aggregates in myotilinopathies and in desminopathies may be related with UBB⁺¹/abnormal protein complexes which are resistant to proteasome degradation. Furthermore, these observations suggest a relationship between the presence of p62 and the formation of inclusions in different subtypes of myofibrillar myopathies.     

Anticholinesterase Activity of Histamine H2-Receptor Antagonists in the Dog: Their Possible Role in Gastric Motor Activity

We studied the anticholinesterase activity of three H₂-receptor antagonists (cimetidine, ranitidine, and famotidine) in vitro and in conscious dogs with chronically implanted strain-gauge force transducers. In vivo, acetylcholine (ACh) was infused intravenously at a dose of 0.05 mg/(kg · min) for 5 minutes with or without a background continuous intravenous infusion of H₂-receptor antagonists or neostigmine during the quiescent period of the interdigestive state. Cimetidine and ranitidine enhanced the ACh-induced contractions in a dose-dependent manner in the gastric antrum, whereas famotidine did not. In vitro, the median inhibitory concentration (IC₅₀) of the acetyl-cholinesterase activity of ranitidine was 3.5 × 10⁻⁶ M, and that of cimetidine 2.5 × 10⁻⁴ M, whereas famotidine had no effect on cholinesterase activity even at concentrations up to 10⁻³ M. The effects of a bolus intravenous injection of the three H₂-receptor antagonists on gastric motor activity also were examined in the digestive state. Cimetidine at 10.0 mg/kg and ranitidine at 3.0 mg/kg significantly increased gastric motor activity. This dose of ranitidine, however, sometimes caused the dogs to collapse and significantly decreased blood pressure in the anesthetized dogs. In conclusion, the H₂-receptor antagonists cimetidine and ranitidine enhanced gastric motor activity through the mechanism of their anticholinesterase activity, but further studies on gastric emptying and the circulatory system are needed.