Modulation of esophageal peristalsis by vagal efferent stimulation in opossum.

Experiments were performed on anesthetized opossums to study the influence of vagal efferent stimulation on peristalsis in the esophageal smooth muscle using various stimulus parameters. Current intensity, pulse duration, frequency, and train duration were varied systematically. Electrical and mechanical activities were recorded simultaneously at 5, 3, and 1 cm above the lower esophageal sphincter (LES). Vagal efferent stimulation produced a spike burst and contraction with a latency after the termination of the stimulus. This latency varied at different sites with the same stimulus parameters. For example, a stimulus of 5 mA, 0.5 ms, 10 Hz, and 1-s train produced latencies for the electrical response of 1.48 +/- 0.04, 2.2 +/- 0.12, and 3.5 +/- 0.09 s (+/- SEM) at 5, 3, and 1 cm above LES, respectively. The differences in latency were statistically significant (P less than 0.01). The latency of response at any one site also changed with different stimulus parameters; e.g. at 1 cm above LES, the latency of electrical response at 10 Hz was 3.5 +/- 0.09 s, but at 20 Hz the latency was 2.01 +/- 0.06 s when current intensity, pulse, and train duration remained at 5 mA, 0.5 ms, and 1 s. This decrease in latency with increasing frequency was statistically significant (P less than 0.01). By changing stimulus parameters, antiperistalsis or peristalsis with different speeds of propagation could be induced. Antiperistalsis or simultaneous responses occurred near threshold stimulus parameters. Suprathreshold stimuli produced peristaltic responses. Speed of peristalsis in the distal esophagus was 1.82 +/- 0.08 cm/s with swallowing, which was not different from 1.98 +/- 0.14 cm/s (P greater than 0.05) with vagal stimulation of 5 mA, 0.5 ms, 10 Hz, and 1-s train. These studies suggest that: (a) peristalsis in the smooth muscle part of the esophagus can be explained entirely on the basis of peripheral mechanisms, and (b) the central nervous system may modulate the occurrence, polarity, and speed of propagation by modifying the intensity and frequency of vagal activation.     

高频腔内超声对胃食管反流患者食管运动功能的评价

目的 应用高频腔内超声与食管测压同步检测胃食管反流病(GERD)患者的食管运动功能异常情况,并尝试论证腔内超声评估食管运动功能异常的有效性和可行性,以及食管压力与食管壁肌层厚度之间的关系.方法 10例经内镜及24 h食管pH检测确诊为GERD的患者,5例正常志愿者作为对照.经鼻腔导入高频超声探头(频率20 MHz,直径1.9 mm)及四通道水灌注式测压导管,在观察静息及吞咽时食管压力变化的同时,同步记录食管的运动影像,并计算出下食管括约肌上端5 cm、10 cm、1 5 cm及20 cm处食管环形肌和纵形肌的收缩指数、收缩周期及食管截面积.同时,通过测压导管同步监测湿咽时食管的最大压力值,计算其与同一位置的食管最大肌层厚度之间的相关性.结果 10例GERD患者与正常对照组相比,食管各段环形肌、纵形肌收缩指数均明显缩小(P＜0.05);收缩周期有延长的趋势;而最大截面积与正常对照组差异无统计学意义(P＞0.05).食管各段的最大压力值与同一部位的最大肌层厚度之间存在正相关(r=0.552～0.736).结论 食管各部位的最大压力值与最大肌层厚度之间存在正相关;GERD患者存在食管运动功能的异常,食管壁的舒缩能力下降以及收缩周期延长可能影响食管的廓清力,从而与GERD的发病有直接关系;同时,高频腔内超声为功能性胃肠病的诊断及其临床研究提供了一种新的方法.     

Experimental induction of isolated lower esophageal sphincter relaxation in anesthetized opossums.

Isolated lower esophageal sphincter (LES) relaxation, defined as a transient sphincteric relaxation unaccompanied by esophageal peristalsis, has been shown to precede most episodes of gastroesophageal reflux in humans. We studied the genesis of isolated LES relaxation in anesthetized opossums by observing the response of four components of the deglutition reflex (mylohyoid electrical activity, pharyngeal contraction, esophageal peristalsis, and LES relaxation) to pharyngeal tactile stimulation, electrical stimulation of superior laryngeal nerve (SLN) afferents or cervical vagal efferents, and to balloon distention of the esophageal body. A single pharyngeal stroking evoked isolated LES relaxation in 56% of 160 instances. The proportion of isolated relaxations in response to SLN electrical stimulation varied inversely with the stimulus frequency, occurring in 64% of the responses at 5 Hz and 4% of the responses at 30 Hz. A full four-component deglutition sequence was most likely to occur at the higher frequencies of SLN electrical stimulation. Esophageal balloon distention elicited isolated LES relaxations or no response at low distending volumes, whereas at higher volumes LES relaxation and esophageal contraction predominated. Isolated LES relaxation had significantly less magnitude than relaxations accompanied by esophageal contractions. Bilateral cervical vagotomy abolished all LES and esophageal body responses induced by pharyngeal stroking and SLN stimulation, and rendered the esophageal body and LES less responsive to small volumes of distention. Vagal efferent stimulation produced isolated LES relaxation at lower frequency stimulation and LES relaxation with esophageal contractions at higher frequency stimulation. These studies show that isolated LES relaxation represents incomplete expression of either the deglutitive reflex or the peripheral reflex mediating secondary peristalsis.     

Activation of cyclic AMP-dependent protein kinase during canine lower esophageal sphincter relaxation

In isolated strips of opossum lower esophageal sphincter (LES) smooth muscle, elevation of cyclic AMP (cAMP) content is associated with relaxation. Because the activation state of cyclic nucleotide-dependent protein kinases may be a more sensitive measure of functionally important changes in cyclic nucleotide levels, we examined the ability of several pharmacological agents and electrical stimulation of the enteric neurons to activate cAMP dependent-protein kinase (cA-PK) and to relax isolated strips of LES smooth muscle. Addition of either isoproterenol or SK&F 94120, a selective inhibitor of the low Km cAMP phosphodiesterase to isolated strips of canine LES produced concentration-dependent increases in the activity ratio of cA-PK and concentration-dependent relaxations of canine LES. In contrast, although both zaprinast (M&B 22948), a selective inhibitor of the cyclic GMP selective phosphodiesterase, and sodium nitroprusside relaxed canine LES neither drug significantly increased the activity ratio of cA-PK. Furthermore, electrical stimulation of the enteric neurons produced a frequency-dependent relaxation but did not significantly activate cA-PK. To eliminate the possibility that the rapid metabolism of cAMP prevented us from observing a significant activation of cA-PK during electrical field stimulation, the ability of electrical field stimulation (1.0 Hz) to activate cA-PK was examined in the presence of 0.1 mM 3-isobutyl-1-methylxanthine. At at concentration of 0.1 mM, 3-isobutyl-1-methylxanthine, by itself, significantly increased the activity ratio of cA-PK; however, there was no additional activation produced by electrical field stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cyclic GMP: a potential mediator of neurally- and drug-induced relaxation of opossum lower esophageal sphincter

Electrical field stimulation (EFS) of isolated strips of opossum lower esophageal sphincter (LES) produced a relaxation that was accompanied by an elevation of intracellular cyclic GMP content. In order to compare the time dependence of the EFS-induced relaxation with that of the elevation of cyclic GMP, the ability of EFS to produce relaxation and increase cyclic GMP was measured. The results of these experiments showed that cyclic GMP content increased before the onset of relaxation. Cumulative addition of atriopeptin II, an activator of particulate guanylate cyclase, produced a concentration-dependent relaxation of this tissue and increased cyclic GMP content. In other experiments, zaprinast, an inhibitor of a cyclic GMP selective-phosphodiesterase, produced a concentration-related relaxation of opossum LES and increased cyclic GMP content. However, pretreatment with zaprinast (3 microM) did not potentiate the EFS-induced relaxation or the increase in cyclic GMP content. At this concentration, however, zaprinast increased the basal content of cyclic GMP. Finally, 8-Br-cyclic GMP, a membrane-permeable analog of cyclic GMP, produced a concentration-dependent relaxation of isolated strips of opossum LES. In conclusion, these data extend the initial findings that an elevation in cyclic GMP content is associated with relaxation and suggest that cyclic GMP is a potential intracellular messenger of neurally- and drug-induced relaxation of opossum LES.     

The Mechanics of Esophageal Muscle Contraction. EVIDENCE OF AN INOTROPIC EFFECT OF GASTRIN

To compare the mechanical properties of lower esophageal sphincter (LES) and esophageal circular smooth muscle, force-velocity determinations were made under various physiological conditions. Isotonic and isometric recordings of opossum circular muscle were used to obtain the velocity of shortening and force, respectively, during alterations in: (a) initial muscle length (preload), (b) afterload, (c) calcium concentration, and (d) gastrin I. Muscle contraction was elicited to the neurogenic response at the termination of electrical stimulation. A change in preload (muscle length) altered the peak force (Po) developed during an afterloaded contraction, but had only a minor effect on the maximum velocity of shortening (V max). At the length of optimal tension development, Lo, (preload, 1.5 g), the LES muscle had a V max of 6.1+/-0.2 mm/s and a Po of 17.7+/-0.7 g. The esophageal muscle at its Lo (preload, 2.0 g) had a V max of 6.3+/-0.5 mm/s and a Po of 18.1+/-1.2 g. A decrease in calcium from 2.5 mM to 1.0 mM significantly reduced the V max and Po of all muscle, but an increase in calcium to 5.0 mM increased these parameters only minimally. At a calcium of 1.0 mM, gastrin I increased both V max and Po of all muscle. This inotropic effect of gastrin I occurred at lower concentrations in LES muscle than in muscle from the upper esophagus. The power (force x velocity) and work (force x muscle shortening) of esophageal and LES muscle were calculated from these data. Both the work and power generated during esophageal and LES muscle contraction were determined by: (a) the initial muscle length as produced by the preload, (b) the afterload against which the muscle was contracting, and (c) the contractility of inotropism of the muscle, that is, the force-velocity curve on which the muscle was operating.     

Lower Esophageal Sphincter Relaxation: Studies on the Neurogenic Inhibitory Mechanism

The purpose of this study was to determine the physiological mechanism of lower esophageal sphincter (LES) relaxation. Circular muscle of the esophagus, LES, and stomach were evaluated for their inhibitory response to electrical stimulation during a maintained tonic contraction produced by a superfusion of acetylcholine and physostigmine. Only the circular muscle of the distal esophagus showed an inhibitory response to electrical stimulation. The maximal inhibition of LES muscle was 63.9+/-5.9 (mean+/-SE)% of the acetylcholine produced tension and occurred at 80 V. Upper esophageal and gastric muscle were not inhibited. The inhibitory response of the LES muscle was antagonized by tetrodotoxin and hexamethonium but not by other specific antagonists. Adrenergic nerve destruction following 6-hydroxydopamine also did not abolish the LES inhibition. These data indicate that the distal esophagus, at the zone of the manometrically determined LES, is characterized by a nonadrenergic neural inhibitory system. We suggest that these nerves may mediate LES relaxation.     

Evidence for muscarinic inhibitory neurotransmission in rodent small intestine

The influence of cholinergic and noncholinergic inhibitory nerves was examined in circular and longitudinal muscle from the duodenum. Rodent proximal small intestine was cut into strips measuring 6.0 x 10.0 mm. Strips cut along the oral-caudal axis were called longitudinal strips, whereas those cut 90 degrees to that axis were called circular strips. The strips were stretched to their optimal lengths and subjected to electrical field stimulation in the presence of various concentrations of atropine, pirenzepine or McN-A-343-11. All three drugs inhibited field-stimulated contraction responses and produced or augmented relaxation responses in both muscle layers. All relaxation responses were abolished by tetrodotoxin, indicating they were due to excitation of inhibitory nerves. For each response examined atropine was significantly more potent than pirenzepine (relative potency ratio, 13.36-95.74). The inhibitory effect of McN-A-343-11 on longitudinal muscle was antagonized by both atropine and pirenzepine, indicating the recruitment of cholinergic inhibitory nerves. Neither atropine nor pirenzepine had any effects on inhibitory responses produced by McN-A-343-11 in circular muscle, indicating the recruitment of noncholinergic inhibitory nerves. McN-A-343-11 also increased spontaneous contraction amplitudes in both muscle layers by a direct (tetrodotoxin-resistant) effect on smooth muscle. This effect was also antagonized by atropine and pirenzepine. Thus, both cholinergic and noncholinergic nerves participate in inhibitory neuromuscular transmission in the small intestine. Circular muscle is dominated by a noncholinergic inhibitory innervation. Longitudinal muscle appears to be controlled by both cholinergic and noncholinergic inhibitory nerves.     

Evidence for diminished inhibitory neuromuscular transmission in distal small intestine

The influence of myenteric nerves on duodenal muscle contraction and relaxation was examined in vitro and compared with muscle responses from the ileum. Proximal and distal rat small intestine was cut into strips measuring 6.0 X 10.0 mm. Strips cut along the oral-caudal axis were called longitudinal strips, whereas those cut 90 degrees to that axis were called circular strips. The strips were stretched to their optimal lengths and subjected to electrical field stimulation (0.1-1.0 msec pulse duration, 30-300 mA, 2-26 Hz) in the presence of Krebs' solution and Krebs' plus atropine, 10(-6) M. Field stimulation produced contraction responses that were inhibited by atropine and relaxation responses that were augmented by atropine. Muscarinic blockade abolished completely contraction in circular muscle, but atropine-resistant contractions persisted in the longitudinal strips. Proximal muscle showed significantly greater relaxation responses compared to distal muscle (P less than .05) at nearly all parameters of pulse duration, current and frequency. Contraction and relaxation amplitudes were significantly greater in longitudinal than respective circular muscle (P less than .05) at either site in the intestine. Thus, not only do the two muscle layers differ in their respective nerve supplies, but inhibitory neuromuscular transmission appears to have a greater influence in proximal than distal intestine.     

Pharmacologic identification of the lower esophageal sphincter

The distal 2/3 of the opossum esophagus contains only smooth muscle. Manometry shows that the most distal 1-2 cm is the lower esophageal sphincter. We used a variety of agonists to seek differences between circular muscle from the sphincteric segment and more rostral levels. Isometric contractions of strips from the distal 6 cm were recorded in vitro in response to acetylcholine, carbachol, methacholine, nicotine. DMPP, norepinephrine, norepinephrine with propranolol, barium, atropine, and potassium. Significant differences in threshold concentration occurred for all drugs except barium, atropine, and potassium, the more distal strips being more sensitive. The gradient of threshold was much steeper for norepinephrine than for the other drugs. Maximal responses did not differ among levels for the choline esters or ganglionic stimulants, but showed proximal diminution for norepinephrine. These differences in threshold concentration could represent differences in distribution density of drug receptor sites, differences in affinity of receptors for the agonists, differences in rates of uptake of agonists, or differences in rates of enzymatic hydrolysis; or they may have no common basis. The sphincter is defined, at least in part, in the esophageal wall rather than in the central nervous system. The greater magnitude of the difference in sensitivity to norepinephrine than for the other agents suggests that the adrenergic innervation is important in defining the lower esophageal sphincter.     

Involvement of endothelial cells in relaxation and contraction responses of the aorta to isoproterenol in naive and streptozotocin-induced diabetic rats

Experiments were designed to investigate the importance of the endothelium in the relaxation of isolated rat aorta caused by a beta adrenoceptor agonist. Mechanical removal of the endothelium attenuated the relaxation induced by isoproterenol (ISO) and did not affect the relaxation produced by forskolin and by sodium nitroprusside. High concentrations of ISO produced an increase in the resting tension of aortic strips with and without endothelium in a concentration-dependent manner. Mechanical removal of the endothelium or treatment with methylene blue enhanced the maximal contraction induced by ISO. Phentolamine antagonized the contractile responses induced by ISO. In the case of streptozotocin-induced diabetic rats, both aortic strips with and without endothelium generated concentration-response curves for ISO-induced relaxation that were shifted to the right. The relaxant responses to forskolin and sodium nitroprusside were not significantly different between vessels from diabetic and age-matched control rats. In both aortic strips with and without endothelium, the maximal contraction in response to high concentrations of ISO was significantly enhanced in strips from diabetic rats. These results suggest that ISO-induced relaxation of aortic strips with endothelium is mediated by beta adrenoceptors on both the endothelium and the smooth muscle, and high concentrations of ISO produce an increase in the resting tension through alpha adrenoceptors. It is further suggested that the decreased relaxant response of the aorta to ISO in diabetes may be due to decreased density or affinity of beta adrenoceptors on the smooth muscle.     

The Esophageal Propulsive Force: Esophageal Response to Acute Obstruction

The response of the normal human esophagus to an obstructing intraluminal bolus was investigated and compared to the response evoked by transient intraluminal distention. A balloon, immobilized within the esophagus by external attachment to a force transducer, was inflated with from 3 to 25 ml of air for from 3 to 210 sec. Pressure phenomena occurring in the esophagus were simultaneously recorded from the body of the esophagus above and below the balloon.Transient distention (5 sec or less) with small volumes (5 ml or less) often evoked a secondary peristaltic wave in the esophagus distal to the balloon, but infrequently resulted in the registration of any force exerted upon the balloon to drive it downward. Conversely, distentions of longer duration and with greater volume elicited an esophageal propulsive force exerted upon the balloon oriented to propel it aborally, and much less often evoked a propagated wave of secondary peristalsis. The propulsive force, obviously resulting from esophageal muscular contraction, occurred promptly, and once initiated, was sustained until deflation of the balloon. It varied widely in magnitude, from 4 to 200 g, and was associated with no motor phenomena recorded from the body of the esophagus proximal or distal to the balloon which could account for its presence, onset, magnitude, or duration. The force was inhibited by deglutition, but arrival of the primary peristaltic wave at the bolus resulted in augmentation of the force. When the obstructing balloon was freed from its attachment, the persistent, stationary force was converted to a propagated one that propelled the balloon before it. It the balloon was arrested before entering the stomach, the moving contraction was also arrested and the persistent propulsive force acting upon the balloon was maintained. The velocity of the moving contraction wave was determined in great part by the resistance offered by the bolus. Unrestrained, the balloon was propelled aborally at 4-8 cm/sec by the esophageal propulsive force; when restrained by 50 g, the rate of passage was reduced to 0.2-0.8 cm/sec.The esophageal response to intraluminal distention is thus not limited to the uninterrupted wave of secondary peristalsis but is versatile and is determined by the nature of the distending bolus. Transient distention by a mobile or collapsible bolus elicits the propagated secondary peristaltic wave.     

Bi‐layer silk fibroin grafts support functional tissue regeneration in a porcine model of onlay esophagoplasty

Partial circumferential, full thickness defects of the esophagus can occur as a result of organ perforation or tumour resection, or during surgical reconstruction of strictured segments. Complications associated with autologous tissue flaps conventionally utilized for defect repair necessitate the development of new graft options. In this study, bi‐layer silk fibroin (BLSF) scaffolds were investigated for their potential to support functional restoration of partial circumferential defects in a porcine model of esophageal repair. Onlay thoracic esophagoplasty with BLSF matrices (~3 x 1.5 cm) was performed in adult swine (N = 6) for 3 months of implantation. All animals receiving BLSF grafts survived with no complications and were capable of solid food consumption. Radiographic esophagrams revealed preservation of organ continuity with no evidence of contrast extravasation or strictures. Fluoroscopic analysis demonstrated peristaltic contractions. Ex vivo tissue bath studies displayed contractile responses to carbachol, electric field stimulation, and KCl while isoproterenol produced tissue relaxation. Histological and immunohistochemical evaluations of neotissues showed a stratified, squamous epithelium, a muscularis mucosa composed of smooth muscle bundles, and a muscularis externa organized into circular and longitudinal layers, with a mix of striated skeletal muscle fascicles interspersed with smooth muscle. De novo innervation and vascularization were observed throughout the graft sites and consisted of synaptophysin‐positive neuronal boutons and vessels lined with CD31‐positive endothelial cells. The results of this study demonstrate that BLSF scaffolds can facilitate constructive remodeling of partial circumferential, full thickness esophageal defects in a large animal model. Copyright © 2017 John Wiley & Sons, Ltd.     

Divergent pharmacological effects of three calmodulin antagonists, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), chlorpromazine and calmidazolium, on isometric tension development and myosin light chain phosphorylation in intact bovine tracheal smooth muscle

To investigate the usefulness of calmodulin antagonists in intact cell systems, effects of three calmodulin antagonists, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), chlorpromazine (CPZ) and calmidazolium on isometric tension development and myosin light chain (P-LC) phosphorylation in bovine tracheal smooth muscle strips were compared to inhibition of purified myosin light chain kinase activity. These antagonists inhibited the Ca++-calmodulin-induced activation of myosin light chain kinase in a concentration-dependent manner, with IC50 values of 1.0 (calmidazolium), 25 (W-7) and 65 microM (CPZ), respectively. Inhibitory effects of these antagonists were abolished with increasing concentrations of calmodulin. However, when these antagonists were used in intact smooth muscle strips, the gradation of potencies did not parallel the anticalmodulin activities. W-7 (100 microM) exhibited a similar extent of antagonism between the contractile responses to carbachol and KCl. The increase in P-LC phosphate content in response to 1-min stimulation with 10(-5) M carbachol was inhibited by W-7. CPZ exhibited an unexpectedly potent antagonism on carbachol-induced isometric tension development and P-LC phosphorylation. Atropine showed an antagonism similar to CPZ. CPZ and verapamil had similar antagonistic effects on KCI-induced contractions. Calmidazolium (50 microM) produced no significant inhibition on carbachol-induced isometric tension development and P-LC phosphorylation in intact smooth muscle strips. It may be concluded that 1) W-7 antagonizes the smooth muscle contraction through the inhibition of the initial increase in the P-LC phosphorylation; 2) CPZ produces effects other than calmodulin antagonism; and 3) calmidazolium is not effective in intact smooth muscle strips.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of successive vagal stimulations on contractions in esophageal smooth muscle of opossum.

Studies were performed in anesthetized opossums to investigate the influence of successive vagal stimuli on esophageal contractions. Mechanical activity was recorded manometrically 5 cm above the lower esophageal sphincter. Contractions in the esophagus were evoked by electrical stimuli of 2.5 mA, and 1-ms pulse duration applied to the cervical vagi, at various train durations and frequencies. Paired or multiple stimuli of 1-s train length were also tested at different interstimulus intervals (ISI). Paired stimuli at an ISI of less than or equal to 3 s and at a frequency of less than or equal to 10 Hz showed refractoriness, i.e., the contractions to the first stimulus inhibited the contraction to the second stimulus. A frequency of 50 Hz showed initial inhibition, i.e., the second stimulus inhibited the contraction to the first stimulus. Repetitive stimuli applied at a rate of 8/min (ISI 6.5 s) evoked contractions to each stimulus. At 15/min, every second or third contraction was inhibited. With stimuli applied at 30/min, contractions occurred only in response to the first and/or the last stimulus; depending upon the frequency of vagal stimulation. The intervening stimuli did not evoke any contractions. A long train stimulus produced an initial, a terminal, or both contractions depending on the stimulation value. These studies show that (a) vagal efferent stimulation causes initial inhibition and refractoriness in the esophageal smooth muscle; (b) the degree of initial inhibition increases with increasing frequency of stimulation; (c) the occurrence of contractions only at the onset and the end of a long train stimulus may be due to the influence of initial inhibition and refractoriness.     

Influence of bolus temperature on human esophageal motor function

Hot and cold water, in comparison to room temperature water, ingested by normal young men, profoundly alters esophageal motor function. Cold water slows or abolishes esophageal peristalsis, prolongs the contraction wave in the distal esophagus, produces a delayed but prolonged relaxation of the lower esophageal sphincter, and regularly causes a lower esophageal sphincteric contraction of increased amplitude. It does not, however, diminish the frequency of response of the lower esophageal sphincter even when the peristaltic wave above is abolished. Hot water, on the other hand, accelerates the response of the esophagus to the swallow; this change is reflected by increased speed of wave propagation, waves of shorter duration, a more brief relaxation of the lower esophageal sphincter, and a lower esophageal sphincter contraction of less amplitude. Hot water may even increase the frequency of peristalsis at least in the proximal esophagus. In spite of these changes, however, neither extreme of temperature altered the rapid passage of the water swallows through the more proximal portions of the esophagus. Hot water tended to traverse the lower esophageal sphincter more rapidly than did room temperature water, but cold water was often delayed in entering the stomach and tended to pool in the distal esophagus even though sphincteric relaxation was manometrically complete and prolonged.     

Effects of 5-hydroxytryptamine on the lower esophageal sphincter in vivo: evidence for multiple sites of action.

Intravenous administration of 5-hydroxytryptamine (5-HT) caused a dose-dependent contraction in the lower esophageal sphincter in the opossum. The smallest dose of 5-HT which caused a detectable contraction of the sphincter was 0.5 mug/kg, and a maximal sphincter contraction was produced by a dose of 40 mug/kg. Methysergide converted the contractile effect of 5-HT to a dose-dependent fall in the sphincter pressure; maximal inhibition of 77.2 +/- 7.2% of the resting pressure occurred with a dose of 40 mug/kg. The inhibitory effect of 5-HT was antagonized by tetrodotoxin, 5 MeO-DMT, and 5-HT tachyphylaxis. 5 MeO-DMT enhanced 5-HT-induced contraction of the sphincter. In the presence of 5 MeO-DMT and methysergide, 5-HT still caused a brief contraction of the sphincter; this contraction appeared to be due to stimulation of postganglionic cholinergic neurons as it was antagonized by tetrodotoxin or atropine. Reserpinization caused enhancement of the sphincter contraction by 5-HT. In the reserpinized animals in the presence of methysergide, 5-HT caused a small initial contraction followed by prolonged inhibition; atropine antagonized the initial contraction, while inhibition was antagonized by 5 MeO-DMT. These studies are consistent with the view that 5-HT exerts several different effects on the sphincter. 5-HT causes contraction of the sphincter by its direct action on the muscle and also by stimulation of cholinergic excitatory neurons. In addition, 5-HT inhibits the sphincter by stimulation of nonadrenergic inhibitory neurons.     

Inhibitors of neutral endopeptidase potentiate electrically and capsaicin-induced noncholinergic contraction in guinea pig bronchi

To evaluate the role of airway neutral endopeptidase (NEP) in the regulation of contraction of airway smooth muscle in response to endogenous tachykinins, we studied the effects of the NEP inhibitor phosphoramidon on contractions of guinea pig bronchial smooth muscle strips induced by either electrical field stimulation (EFS) or by capsaicin. In the presence of atropine (10(-6) M), propranolol (10(-6) M), phentolamine (10(-5) M), indomethacin (10(-6) M) and pyrilamine (5 x 10(-6) M) EFS (biphasic; pulse width, 1.0 msec; frequency 0.5-5 Hz for 30 sec; intensity, 20 V) produced noncholinergic, nonadrenergic muscle contraction in a frequency-dependent fashion (P less than .001). Phosphoramidon potentiated the contractile responses to EFS (P less than .01). Leucine-thiorphan (10(-5) M), another NEP inhibitor, potentiated EFS-induced contraction in a similar fashion as phosphoramidon (186 and 182% of control, respectively; each comparison, P less than .025). Captopril, bestatin, leupeptin and physostigmine (each drug, 10(-5) M) were without effect (P greater than .5, N = 5). Capsaicin (1.5 x 10(-8) M) produced long-lasting atropine-resistant smooth muscle contraction, an effect potentiated by phosphoramidon (10(-5) M (P less than .001). Removal of the epithelium slightly but significantly (P less than .05) increased the contractile responses to capsaicin and to EFS at impulse frequencies of 2 and 5 Hz, and phosphoramidon substantially increased contractions in tissues without epithelium. The trachea, bronchi and lungs each contained significant NEP activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Platelet-induced neurogenic coronary contractions due to accumulation of the false neurotransmitter, 5-hydroxytryptamine.

The purpose of this study was to determine if 5-hydroxytryptamine released from aggregating platelets could be accumulated and released by canine coronary adrenergic nerves, and if the false neurotransmitter resulted in an abnormal response of the smooth muscle to nerve stimulation. Isometric tension was measured in rings of epicardial coronary suspended in organ chambers filled with physiological salt solution. The response to electrical stimulation or exogenously added norepinephrine was elicited after contraction with prostaglandin F2 alpha. Electrical stimulation and exogenous norepinephrine caused beta-adrenergic relaxation of control rings. However, after rings were exposed for 2 h to aggregating platelets or 5-hydroxytryptamine, electrical stimulation caused frequency-dependent contractions. These contractions were prevented by the serotonergic antagonists, cyproheptadine or ketanserin, or by the neuronal uptake inhibitor, cocaine. The relaxation caused by exogenously added norepinephrine was unchanged after exposure to platelets or 5-hydroxytryptamine, indicating that smooth muscle alpha- and beta-adrenergic responsiveness was unchanged. The electrically stimulated overflow of radiolabeled norepinephrine from superfused strips of coronary artery was not altered by prior exposure to 5-hydroxytryptamine, indicating that the effect of exposure on the response to electrical stimulation is primarily at smooth muscle serotonergic receptors. Canine coronary arteries accumulated and metabolized radiolabeled 5-hydroxytryptamine in vitro. The accumulation of 5-hydroxytryptamine was inhibited by cocaine or by adrenergic denervation with 6-hydroxydopamine but unaffected by removal of endothelium, indicating that the adrenergic nerves were the primary site of accumulation. Electrical stimulation of superfused strips of coronary artery preincubated with radiolabeled 5-hydroxytryptamine caused the release of the intact indoleamine; this was blocked by the neurotoxin, tetrodotoxin. These studies suggest that 5-hydroxytryptamine liberated from aggregating platelets may be accumulated by coronary adrenergic nerve endings. Upon its release from the nerves as a false transmitter, the amine can activate serotonergic receptors on the smooth muscle and reverse the action of the adrenergic nerves from dilator to constrictor.