The cardiac sphincter in the cat

The role of the superior laryngeal nerve in esophageal reflexes

The aim of this study was to determine the role of the superior laryngeal nerve (SLN) in the following esophageal reflexes: esophago-upper esophageal sphincter (UES) contractile reflex (EUCR), esophago-lower esophageal sphincter (LES) relaxation reflex (ELIR), secondary peristalsis, pharyngeal swallowing, and belch. Cats (N = 43) were decerebrated and instrumented to record EMG of the cricopharyngeus, thyrohyoideus, geniohyoideus, and cricothyroideus; esophageal pressure; and motility of LES. Reflexes were activated by stimulation of the esophagus via slow balloon or rapid air distension at 1 to 16 cm distal to the UES. Slow balloon distension consistently activated EUCR and ELIR from all areas of the esophagus, but the distal esophagus was more sensitive than the proximal esophagus. Transection of SLN or proximal recurrent laryngeal nerves (RLN) blocked EUCR and ELIR generated from the cervical esophagus. Distal RLN transection blocked EUCR from the distal cervical esophagus. Slow distension of all areas of the esophagus except the most proximal few centimeters activated secondary peristalsis, and SLN transection had no effect on secondary peristalsis. Slow distension of all areas of the esophagus inconsistently activated pharyngeal swallows, and SLN transection blocked generation of pharyngeal swallows from all levels of the esophagus. Slow distension of the esophagus inconsistently activated belching, but rapid air distension consistently activated belching from all areas of the esophagus. SLN transection did not block initiation of belch but blocked one aspect of belch, i.e., inhibition of cricopharyngeus EMG. Vagotomy blocked all aspects of belch generated from all areas of esophagus and blocked all responses of all reflexes not blocked by SLN or RLN transection. In conclusion, the SLN mediates all aspects of the pharyngeal swallow, no portion of the secondary peristalsis, and the EUCR and ELIR generated from the proximal esophagus. Considering that SLN is not a motor nerve for any of these reflexes, the role of the SLN in control of these reflexes is sensory in nature only.

Neuronal control of the gastric sling muscle of the guinea pig

The gastric sling (oblique) muscle (GSM), located close to the lower esophageal sphincter (LES), is involved in gastric motor function and may cooperate with the LES in controlling propulsion between the esophagus and stomach. Neuronal pathways and transmission to the GSM were investigated in isolated esophagus-stomach preparations by using intracellular recording with the focal electrical stimulation and neuroanatomical tracing method. Focal stimulation on the GSM evoked inhibitory junction potentials (IJPs) that were reduced to 45% by 100 microM N-nitro-L-arginine and subsequently blocked by 0.5 microM apamin, thereby unmasking excitatory junction potentials (EJPs), which were abolished by 1 microM hyoscine. Vagal and esophageal stimulation evoked IJPs that were blocked by 100 microM hexamethonium. Vagal stimulation also evoked EJPs after blockade of IJPs. Application of 1,1'-didodecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate to the GSM labeled muscle motor neurons located in the stomach mainly close to the GSM, with a few neurons (2%) in the esophagus. The majority (79%) of labeled neurons were immunoreactive for choline acetyltransferase and, hence, excitatory motor neurons. Inhibitory motor neurons (nitric oxide synthase immunoreactive; 15%) were clustered in the midline near the gastroesophageal region. These results demonstrate that the GSM is innervated primarily by gastric excitatory and inhibitory motor neurons and some esophageal neurons. Both excitatory (acetylcholine) and inhibitory (nitric oxide and apamin-sensitive component) transmission can be activated via vagal-enteric pathways.

Investigation of oesophageal reflux symptoms after gastric surgery with combined pH and bilirubin monitoring

BACKGROUND

Little is known about the role of bile in gastro-oesophageal reflux disease in patients with previous gastric surgery. This has partly been due to a lack of suitable techniques for identifying bile reflux objectively.

METHODS

Some 28 patients with reflux symptoms and previous gastric surgery underwent oesophageal manometry, and 24-h ambulatory oesophageal pH and bilirubin monitoring.

RESULTS

A wide variety of operations had been performed, most commonly Pólya gastrectomy (seven patients), vagotomy and pyloroplasty (six) and vagotomy and gastrojejunostomy (four). Three patients had isolated acid reflux, eight had isolated bile reflux, six had combined acid and bile reflux, and 11 patients had no reflux. Two-thirds of heartburn symptoms were not associated with reflux. However, one-quarter were associated with acid reflux and only 7 per cent with bile reflux. Erosive oesophagitis was present in five patients: two with combined acid and bile reflux, and three with isolated bile reflux.

CONCLUSION

Acid and/or bile reflux can be present after a wide variety of gastric operations. Symptoms are more frequently associated with acid reflux than with bile reflux. Erosive oesophagitis can occur in the presence of isolated bile reflux. Combined pH and bilirubin monitoring determines the nature of the refluxate, and may help in the management of these patients.

GABA receptors in the dorsal motor nucleus of the vagus influence feline lower esophageal sphincter and gastric function

Gamma-aminobutyric acid (GABA) antagonist (bicuculline methiodide, BIC; picrotoxin, PIC) or agonist (muscimol, MUS) microinjections were made into the dorsal motor nucleus of the vagus nerve (DMV), and effects on lower esophageal sphincter pressure (LESP), gastric motility, and gastric acid secretion were determined in chloralose-anesthetized cats. Right or left DMV sites were microinjected with BIC, PIC, MUS, or isotonic tonic saline (140 nl) through a glass micropipette having a tip diameter of 15-21 microns. Esophageal body, LESP, and gastric fundic pressures were measured manometrically. Circular smooth muscle contractions of the antrum and pylorus were recorded with strain-gauge force transducers. Gastric acid secretion was measured every 15 min through a gastric cannula and titrated to pH 7.0. DMV microinjection sites were verified histologically. Direct BIC microinjections (0.275 or 0.550 nmol) into the DMV primarily produced a decrease in LESP (71% of all sites tested), with mean LESP changing from 23.2 +/- 1.7 mmHg to 3.7 +/- 0.7 mmHg (p < 0.01). Tonic LESP increases and phasic LESP contractile activity occurred less frequently. BIC-induced LESP responses were abolished by vagotomy or by microinjections of MUS (0.5 to 10 nmol) into the DMV. Direct PIC microinjection (0.232 nmol) into the DMV produced a pattern of responses similar to those observed with BIC (which were also abolished by vagotomy or by MUS microinjections into the DMV). The antrum and pylorus were also responsive to DMV microinjections of both GABA antagonists. Microinjections of BIC or PIC into the DMV produced increases in gastric circular muscle activity that occurred less frequently than LESP effects, but also were eliminated by vagotomy. The high (0.550 nmol) dose of BIC increased gastric motility significantly more often than the low dose of BIC (p < 0.05). In addition, BIC (0.550 nmol) microinjections into the DMV increased gastric secretory volume (from 0.6 +/- 0.2 to 6.0 +/- 2.5 ml/15 min; p < 0.01) and total titratible acid (from 34.4 +/- 8.9 to 86.0 +/- 19.1 mEq/15 min; p < 0.01), and decreased gastric pH (from 4.63 +/- 0.44 to 3.50 +/- 0.49; p < 0.05). Vagotomy also eliminated the gastric secretory effects of DMV BIC. Direct microinjections of MUS into the DMV also blocked BIC- or PIC-induced changes in gastric motility and/or gastric acid secretion. Isotonic saline microinjected into the DMV did not increase basal or decrease stimulated gastric esophageal motility or gastric secretion. These data indicate that LESP, gastric motility, and gastric secretion are influenced by a tonic DMV inhibition mediated by GABAA receptor stimulation of the DMV. Because disinhibition of these receptors clearly activates the upper gut, future work should focus on identifying the nuclei providing this synaptic input to the DMV that might be involved in the functional regulation of upper gut motor and secretory function.

Determination of the length and position of the lower oesophageal sphincter (LOS) by correlation of external measurements with combined radiographic and manometric estimations in the cat

Fifty DSH cats were studied radiographically and a highly significant linear correlation was found between the length of the oesophagus measured to the diaphragmatic line on the radiographs and the externally measured distance from the lower jaw incisor teeth to the anterior border of the head of 10th rib. A subsequent manometric study utilizing this correlation in 40 cats suggests that the functional lower oesophageal sphincter (LOS) is situated almost at the level of the diaphragm in the cat. Significant differences were found between the length of the LOS in cats anaesthetized with ketamine compared to alphaxalone-alphadolone or xylazine-ketamine-atropine. The mean lengths of the LOS was 1.42 +/- 0.3 cm. The findings of this study indicate that external measurements can be used to position catheters for accurate oesophageal manometry in the cat.

Central neural control of esophageal motility: a review

We review recent studies on the central neural control of esophageal motility, emphasizing the anatomy and chemical coding of esophageal pathways in the spinal cord and medulla. Sympathetic innervation of the proximal esophagus is derived primarily from cervical and upper thoracic paravertebral ganglia, whereas that of the lower esophageal sphincter and proximal stomach is derived from the celiac ganglion. In addition to noradrenaline, many sympathetic fibers in the esophagus contain neuropeptide Y (NPY), and both noradrenaline and NPY appear to decrease blood flow and motility. Preganglionic neurons innervating the cervical and upper thoracic ganglia are located at lower cervical and upper thoracic spinal levels. The preganglionic innervation of the celiac ganglion arises from lower thoracic spinal levels. Both acetylcholine (ACh) and enkephalin (ENK) have been localized in sympathetic preganglionic neurons, and it has been suggested that ENK acts to pre-synaptically inhibit ganglionic transmission. Spinal afferents from the esophagus are few, but have been described in lower cervical and thoracic dorsal root ganglia. A significant percentage contain calcitonin gene-related peptide (CGRP) and substance P (SP). The central distribution of spinal afferents, as well as their subsequent processing within the spinal cord, have not been addressed. Medullary afferents arise from the nodose ganglion and terminate peripherally both in myenteric ganglia, where they have been postulated to act as tension receptors, and, to a lesser extent, in more superficial layers. Centrally, these afferents appear to end in a discrete part of the nucleus of the solitary tract (NTS) termed the central subnucleus. The transmitter specificity of the majority of these afferents remains unknown. The central subnucleus, in turn, sends a dense and topographically discrete projection to esophageal motor neurons in the rostral portion of the nucleus ambiguous (NA). Both somatostatin-(SS) and ENK-related peptides have been localized in this pathway. Finally, motor neurons from the rostral NA innervate striated portions of the esophagus. In addition to ACh, these esophageal motor neurons contain CGRP, galanin (GAL), N-acetylaspartylglutamate (NAAG), and brain natriuretic peptide (BNP). The physiological effect of these peptides on esophageal motility remains unclear. Medullary control of smooth muscle portions of the esophagus have not been thoroughly investigated.

Motility of the oesophagus and gastro-oesophageal junction during halothane anaesthesia in sheep

Electromanometry and electromyography were used to study gastro-oesophageal motility in two planes of halothane anaesthesia in sheep. Gastro-oesophageal motility when present was greater in light than in deep anaesthesia. The caudal thoracic oesophagus contracted more frequently and for longer than the rostral thoracic oesophagus. In light anaesthesia oesophageal movements were peristaltic in direction with a propagation velocity of 26-29 cm sec-1. Rumen pressures increased throughout anaesthesia and the rate of increase was greatest when the plane of anaesthesia was deep at the start. Gastro-oesophageal reflux (GOR) occurred in both planes of anaesthesia and must occur by passive mechanisms during deep anaesthesia because gastro-oesophageal motility was inhibited. A high pressure zone (HPZ) was demonstrated for a length of 2.9 cm at the gastro-oesophageal junction with a balloon-tipped catheter and a 'pull through' technique. Open-tipped catheters could detect the HPZ but were less sensitive. The pressure in the HPZ was not significantly influenced by the depth of anaesthesia used. In 80% of cases of light anaesthesia an increase in HPZ pressure preceeded the contraction of the cranial sac of the rumen. In deep anaesthesia the HPZ continued to have rhythmic changes in tone. Spontaneous GOR coincided with a maximum gastro-oesophageal pressure gradient in 24% of cases. Rumen insufflation with oxygen provoked GOR at a rumen pressure above 33 mmHg compared with 7.2 mmHg during spontaneous reflux. The study demonstrates that a gastro-oesophageal pressure gradient was not primarily responsible for the initiation of GOR during anaesthesia and that the HPZ at the gastro-oesophageal junction of sheep had some of the properties of a lower oesophageal sphincter and played an important role in the initiation of GOR during anaesthesia.

Manometric evaluation of the feline esophagus

Fifteen healthy mongrel cats were manometrically evaluated to quantitate esophageal function and to establish the feline esophagus as an appropriate model for investigations relevant to human physiology and pathology. Detailed findings are presented in the paper. Characteristics of the upper and lower esophageal high-pressure zones and of esophageal body motility were found to be similar to human values. Response to bethanechol stimulation was also similar to that seen in humans. This study establishes normal manometric values for the feline esophagus and validates it as an appropriate model for investigations of esophageal physiology and pathophysiology.

Reflex activation of the lower oesophageal sphincter in the cat induced by stimulation of the splanchnic afferent fibres

Reflex responses of the lower oesophageal sphincter (l.o.s.) to electrical stimulation of the splanchnic afferent fibres were recorded by electromyographic and manometric techniques. Repetitive stimulation of the central end of a splanchnic nerve induced a long latency excitation of the l.o.s., i.e. bursts of spike potentials concomitant with repetitive phasic contractions. Experiments involving nerve sections showed that the efferent pathways of this reflex were served either by stellate sympathetic and/or splanchnic fibres, or by vagal fibres. These responses were abolished following the administration of atropine. These results show that the splanchnic afferent fibres are involved in l.o.s. reflex motor responses through the activation of the sympathetic and parasympathetic efferent supply to the sphincter.

Reflex excitation and inhibition of the lower oesophageal sphincter induced by gastric distension in the cat

Reflex responses of the lower oesophageal sphincter (l.o.s.) to distension of the stomach were studied by electromyographic and manometric techniques. Distension of the fundus and gastric antrum by inflation of a balloon elicited two types of reflex response of the l.o.s. Thus, whereas excitatory responses were recorded following slight distensions, larger distensions resulted in inhibitory responses. Splanchnic fibres and sympathetic fibres originating from the stellate ganglion, as well as vagal fibres served as the efferent pathways for the excitatory reflex response. The efferent pathways for the inhibitory response involved only vagal fibres.

Aspiration pneumonia: assessing the risk of regurgitation in the cat

Depending on the population characteristics, 12 to 80 per cent of patients undergoing elective surgery exceed the current risk criteria for aspiration pneumonitis (gastric volume greater than or equal to 0.4 ml.kg-1 and pH less than or equal to 2.5), in sharp contrast to the actual incidence of the disorder, estimated at 0.01 per cent. Improved specificity would likely result if the risk of regurgitation was also considered, in addition to the volume and pH criteria. As a first attempt to assess the risk of regurgitation under general anaesthesia, we measured the minimal gastric volume (VR) required to produce regurgitation in cats anaesthetized with ketamine. The mean was 20.8 ml.kg-1 (n = 7, range: 8-41, SD = 7.8). We conclude that the residual gastric volume needed to produce a regurgitation under general anaesthesia is at least 20 times greater than the volume required to produce pulmonary damage by intratracheal injection (0.3 ml.kg-1, assuming a pH of 2.5 or less).

Gastric distention: a mechanism for postprandial gastroesophageal reflux

The occurrence of gastroesophageal reflux after meals may be related to an increase in the rate of transient lower esophageal sphincter (LES) relaxations, the mechanisms of which are not understood. We investigated the effects of gastric distention on LES pressure in 16 normal subjects and 17 patients with gastroesophageal reflux disease. Intraluminal pressure was measured in the gastric fundus, LES, and esophageal body with a manometric catheter incorporating a sleeve device. Gastric distention was performed by injecting 0, 250, 500, or 750 ml of air in randomized order into a balloon and maintaining each stimulus for 15 min. Gastric distention did not significantly alter resting LES pressure in either group. During the basal period the rate of transient LES relaxation in the reflux patients (1.1 +/- 0.4 per 15 min) was greater than that in the normal subjects (0.6 +/- 0.1 per 15 min). Gastric distention resulted in a significant threefold to fourfold increase in the rate of transient LES relaxations in both groups. The reflux patients had a significantly greater proportion of complete relaxations (87%) than did the normal subjects (73%). We conclude that gastric distention, by significantly increasing the rate of transient LES relaxations in both normal subjects and patients with gastroesophageal reflux disease, may contribute to the postprandial increase in gastroesophageal reflux.

Effect of an oral beta2-adrenergic agonist on lower esophageal sphincter pressure in normals and in patients with achalasia

The effect of the beta2-adrenergic agonist, carbuterol, was studied on the lower esophageal sphincter (LES) pressure in normals and in patients with achalasia. In normals, the mean LES pressure decreased from 23.1 +/- 6.2 mm Hg (mean +/- SEM) to 16.0 +/- 5.0 mm Hg at a 4.0-mg dose of carbuterol (P less than 0.05). In patients with achalasia, the mean LES pressure decreased from 50.1 +/- 5.1 mm Hg to 22.7 +/- 2.4 mm Hg after a 4.0-mg dose of carbuterol (P less than 0.01). The duration of action following oral administration exceeded 90 min. These studies indicate that the LES in man has beta2-adrenergic receptors that mediate a reduction in pressure. The magnitude of LES pressure reduction in patients with achalasia suggests that this drug may be of therapeutic benefit.

Mechanism of the noradrenergic motor control on the lower oesophageal sphincter in the cat

1. The release of labelled acetylcholine has been measured on lower oesophageal sphincter (l.o.s.) muscular strips previously loaded with tritiated choline. 2. This release was greatly increased by noradrenaline 10(-5) g/ml. and unaffected by atropine 10(-6) g/ml., but it was practically abolished if hemicholinium 5.2 X 10(-4) M was added to the incubating bath containing the tritiated choline. 3. A radioautographic study of sections of l.o.s. strips loaded with tritiated choline showed that the radioactivity was mainly located in the nervous cells of the enteric plexuses and that the muscular cells were very poorly labelled. 4. The increased release of acetylcholine induced by noradrenaline did not occur in a Ca2+-free or in a hypermagnesic Tyrode (12 mM). 5. Tetrodotoxin 10(-6) G/ml. had no effect on the increased release of acetylcholine induced by noradrenaline. In addition, sucrose gap recordings showed that the depolarizing effect of noradrenaline on l.o.s. muscular strips was unaffected by tetrodotoxin 10(-6) g/ml. 6. It is concluded that acetylcholine released in the l.o.s. under the action of noradrenaline originated from the synaptic endings of the cholinergic intramural neurones.

Effect of hemorrhagic hypotension and hypoventilation on lower esophageal sphincter pressure

Dysfunction of the lower esophageal sphincter has been demonstrated in the cat shock model. Analogies have been drawn to reflux and aspiration in the critically ill patient. In a cat shock model, lower esophageal sphincter pressure is reduced and response to bethanechol is impaired. Upon resuscitation to basal state with heparinized shed blood, the lower esophageal basal pressure returns to normal values, and response to bethanechol is restored. This model may explain reflux and aspiration in the critically ill patient.

Sympathetic control of lower oesophageal sphincter motility in the cat

1. The action of adrenaline, noradrenaline and efferent sympathetic fibres on the smooth muscle of the lower oesophageal sphincter (l.o.s.) was studied in vivo on the anaesthetized cat and in vitro with the sucrose gap method. 2. Adrenaline and noradrenaline produce a marked depolarization of the circular muscle of the l.o.s. This effect is suppressed by dihydroergotamine or phentolamine, and greatly reduced by atropine; it remains unaltered by hexamethonium. 3. Sympathetic fibres are excitatory for the l.o.s. They come from the stellate ganglion or run along the splanchnic nerve: the fibres arising from the stellate ganglion (mainly by the cardiac branch of the ganglion) join the vagus nerve at the thoracic level; the fibres running along the splanchnic nerve pass through the coeliac ganglion without synapsing; their cellular bodies lie probably in the ganglia of the sympathetic chain. 4. Repetitive stimulation (20--40 Hz) of these fibres induce, with a latency of 5--8 sec, a sustained or rhythmic contraction of the l.o.s. This response is suppressed by dihydroergotamine, and greatly reduced by atropine, while hexamethonium has no effect. 5. Stimulation of sympathetic fibres induces a facilitation of the vagal excitatory responses and an inhibition of the vagal inhibitory responses of the l.o.s. 6. Our data show that the sympathetic response of the l.o.s. results from the stimulation of adrenergic receptors which are located not only on muscular fibres but also, and chiefly, on intrinsic neurones. Thus, the sympathetic control of the l.o.s. is mainly exerted through cholinergic myenteric neurones which could be excited either directly or indirectly by inhibition of inhibitory intrinsic neurones.

On the relationship between gastric pH and pressure in the normal human lower oesophageal sphincter

The effect upon the lower oesophageal sphincter (LOS) of acid in the proximal stomach was investigated in 12 young healthy subjects. The cardia was perfused in turn with solutions at pH 7, 4, 3, 2, and 1, during successive withdrawals of three perfused pressure-recording catheters, openings of which were at the same axial level. Although there was considerable individual variation, there was a direct and significant relationship between LOW pressure and the acidity of the solution perfused. The results suggest that resting LOS pressure and the acidity of the solution perfused. The results suggest that resting LOS pressure may be determined in part by the pH of the gastric content.

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.

Nature of the vagal inhibitory innervation to the lower esophageal sphincter

The purpose of the present study was to investigate the nature of the vagal inhibitory innervation to the lower esophageal sphincter in the anesthetized opossum. Sphincter relaxation with electrical stimulation of the vagus was not antagonized by atropine, propranolol, phentolamine, or by catechloamine depletion with reserpine. A combination of atropine and propranolol was also ineffective, suggesting that the vagal inhibitory influences may be mediated by the noncholinergic, nonadrenergic neurons. To determine whether a synaptic link with nicotinic transmission was present, we investigated the effect of hexamethonium on vagal-stimulated lower esophageal sphincter relaxation. Hexamethonium in doses that completely antagonized the sphincter relaxation in response to a ganglionic stimulant, 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), did not block the sphincter relaxation in response to vagal stimulation at 10 pulses per second, and optimal frequency of stimulation. A combination of hexamethonium and catecholamine depletion was also ineffective, but hexamethonium plus atropine markedly antagonized sphincter relaxation (P less than 0.001). Moreover, 4-(m-chlorophenyl carbamoyloxy)-2-butyltrimethylammonium chloride (McN-A-343), a muscarinic ganglionic stimulant, also caused relaxation of the lower esophageal sphincter. We suggest from these results that: (a) pthe vagal inhibitory pathway to the sphincter consists of preganglionic fibers which synapse with postganglionic neurons: (b) the synaptic transmission is predominantly cholinergic and utilizes nicotinic as well as muscarinic receptors on the postganglionic neuron, and; (c) postganglionic neurons exert their influence on the sphincter by an unidentified inhibitory transmitter that is neither adrenergic nor cholinergic.

Neural control of the lower esophageal sphincter: influence of the vagus nerves

We performed studies in the opossum to define the influence of the vagi in the control of lower esophageal sphincter (LES) function. Bilateral vagotomy caused transient sphincter hypertension which was prevented by phentolamine and by atropine. Stimulation of the peripheral end of vagus, after bilateral cervical vagotomy, caused relaxation of the LES over a wide range of frequency and intensity of electrical stimulation. The relaxation was less marked at the lower frequencies of stimulation, and atropine treatment did not enhance this relaxation. In other experiments, atropine treatment reversed the rise in gastric (fundic) pressure with the vagal stimulation, but atropine did not enhance the degree of LES relaxation. Stimulation of the central end of the vagus caused an increase in LES pressure due to a centrally mediated reflex; the efferents for this motor response were not present in the vagi, as the reflex contraction persisted after bilateral vagotomy. The LES contraction with the stimulation of the vagal afferents was antagonized by phentolamine as well as by atropine. These studies suggest that: (a) the vagi do not mediate any cholinergic excitatory influences to the LES and the vagal influence of the sphincter is entirely inhibitory; (b) the vagi carry afferent fibres for a centrally mediated neural reflex which contracts the LES, but the efferent path of this reflex arc does not lie in the vagi.

Contractions of the caudal region of the oesophagus of the cat

1. The motility of the most caudal part of the oesophagus has been investigated in cats which were decerebrated, had the whole of the central nervous system pithed or were anaesthetized with chloralose.2. Contractions of the most caudal region of the oesophagus were evoked by its stretch and the presence in it of HCl. These reactions were obtained in all types of preparations used.3. In decerebrate preparations oesophageal contractions occurred in response to the introduction of acid into the stomach. These were not obtained after the vagus nerves had been cut.4. Slight degrees of gastric distension stimulated oesophageal contractions, greater distension was inhibitory.5. Both reductions in oesophageal activity and contractions of the oesophagus were obtained with different parameters of stimulation of efferent vagal fibres.6. Excitatory and inhibitory effects on the oesophagus were obtained from stimulation of the central end of the vagus nerves cut in the abdomen or in the neck.7. In totally pithed preparations of cats stretch of one region of the oesophagus was found to modify the activity of a distant region of the oesophagus cranial or caudal to the site of distension.8. The reactions of the caudal oesophagus were abolished by atropine.9. The importance of vago-vagal reflexes in the modification of basically direct oesophageal responses has been discussed.

A study in vivo of adrenergic receptors in the rectum and in the internal and sphincter of the cat

THE SMOOTH MUSCLE SPHINCTERIC ACTIVITY OF THE ANUS IN CATS IS BASED ON TWO DISTINCT MECHANISMS: a typical anal component, characterized by anal slow pressure waves not related to spike potentials in the internal anal sphincter, and an intestinal-like pressure component related to spiking activity in the internal sphincter. Anal slow pressure waves are influenced by the activity of alpha excitatory receptors within the internal sphincter, whereas no conclusive data are available concerning the action of adrenergic beta receptors on this pressure component. Intestinal-like pressure waves and the correlated spiking activity in the internal anal sphincter are influenced by alpha and beta inhibitory adrenergic receptors. The rectal wall of the cat contains alpha and beta adrenergic receptors producing relaxation.

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.

Effect of pH changes on the cardiac sphincter

In 16 normal subjects the pressure characteristics of the cardiac sphincter have been examined. The effect of perfusing the gastric aspect of the sphincter mucosa has been studied by comparing the effects of saline with those of solutions where pH ranged from 1.0 to 8.0. Acid perfusion produced an increase in sphincteric pressure, particularly at pH 3.0. This suggests that a physiological mechanism exists which can increase the barrier pressure to gastrooesophageal reflux during periods of active secretion of the stomach, as occurs in digestion.