Effect of motilin on the lower esophageal sphincter of the opossum

We have studied the effect of Yajima's synthetic motilin on the lower esophageal sphincter (LES) of the opossum and compared its potency to that of gastrin and its interaction with secretin. Dose-response curves for the LES were constructed from the intravenous bolus injection of graded doses of motilin and gastrin alone and motilin given against a background infusion of secretin. The smallest dose of motilin that elicited a significant response was 0.05 microng/kg, and the highest response was observed with the highest dose used in this study (1.0 microng/kg). Over a wide dose range, both motilin and gastrin were found to be equally potent in stimulating the LES of the opposum, and secretin caused inhibition of the LES pressure to motilin. Therefore, we conclude that (1) motilin is a potent stimulant of the LES; (2) this response is dose dependent; (3) motilin's potency is similar to that of gastrin; and (4) secretin counteracts the effect of motilin on the LES.     

Characterization and mediation of inhibitory junction potentials from opossum lower esophageal sphincter

BACKGROUND: Activating nonadrenergic, noncholinergic (NANC) nerves of the lower esophageal sphincter (LES) hyperpolarizes and relaxes its circular smooth muscle. This relaxation is mediated by nitric oxide (NO) or an NO-containing compound. These studies were undertaken to compare the electrophysiological responses of circular smooth muscle from the LES and esophagus in response to NANC nerve stimulation and to test the hypothesis that NO mediates LES hyperpolarization. METHODS: The transmembrane potential difference was recorded with glass microelectrodes. Nerve-mediated membrane responses were evoked by electrical pulses of 0.5 msec duration and 50 V amplitude. RESULTS: Responses of LES muscle differed from those of the esophageal muscle. The duration of hyperpolarization was much longer in sphincteric muscle. The depolarization that followed hyperpolarization of esophageal muscle was not observed in sphincteric muscle. NG-nitro-L-arginine, an inhibitor of NO synthase, attenuated the nerve-induced hyperpolarization. L-arginine, the substrate for NO synthase, antagonized the effect of NG-nitro-L-arginine. Exogenous NO hyperpolarized of the smooth muscle membrane. CONCLUSIONS: These data support the hypothesis that NO or an NO-like compound may mediate nerve-induced hyperpolarization of the opossum LES.     

Electrophysiological and pharmacological responses of chronically denervated lower esophageal sphincter of the opossum

BACKGROUND & AIMS: Achalasia is characterized by loss of myenteric neurons and incomplete relaxation of the lower esophageal sphincter (LES). The aim of this study was to develop an achalasia model in the opossum using the surfactant benzyldimethyltetradecylammonium chloride (BAC). This study further characterizes the achalasia model. METHODS: BAC or saline was injected circumferentially into the LES of 14 adult opossums. Eight months after injection, manometry, isolated muscle bath studies, electrical field stimulation, and histochemical analysis were performed. RESULTS: Manometrically, the LES of BAC-treated opossums showed higher pressures (38.7 +/- 12 mm Hg vs. 17 +/- 3.0 mm Hg) and reduced esophageal body contraction amplitudes (4.2 +/- 3 mm Hg vs. 27.4 +/- 12 mm Hg). Isolated muscle strips challenged with carbachol and sodium nitroprusside contracted and relaxed similarly to controls. Electrical field stimulation failed to induce relaxation in BAC-treated tissue but did induce contraction. Contractile responses were markedly reduced by tetrodotoxin and atropine in BAC-treated animals and controls. An altered nitric oxide system was shown by the lack of response to L-arginine and N omega-nitro-L-arginine. Histology showed loss of myenteric neurons and increased cholinergic nerve bundles. CONCLUSIONS: Loss of NO inhibitory myenteric neurons markedly reduces the relaxation of the LES, and histology and pharmacological responses suggest a proliferation of cholinergic nerves into the LES contributing to the static elevated pressures of the amyenteric LES.     

Effect of cholecystokinin-octapeptide on lower esophageal sphincter

The effect of cholecystokinin-octapeptide (CCK-OP) on the lower esophageal sphincter (LES) was studied in 50 cats in vivo. CCK-OP caused a dose-dependent fall in LES pressures in all but 4 animals. Maximal sphincter relaxation was obtained with 200 to 400 ng of CCK-OP per kg of body weight. Atropine sulfate and/or hexamethonium, or adrenergic blocking agents (phentolamine or propranolol), in doses that completely inhibit the action of maximal doses of their respective agonists, failed to block the CCK-OP effect. Tetrodotoxin, however, in doses that denervates the LES, antagonized the CCK-OP-induced sphincter relaxation. In these tetrodotoxin-treated animals, CCK-OP produced LES contraction similar to that observed after pentagastrin. These results suggest that CCK-OP stimulates the postganglionic nonadrenergic, noncholinergic inhibitory neurons responsible for sphincter relaxation. CCK-OP also stimulates the circular muscle by direct action causing LES contraction. The latter becomes apparent when the innervation of the LES is abolished by tetrodoxtin.     

Nitrergic modulation of cholinergic responses in the opossum lower oesophageal sphincter

1. Electrical field stimulation (EFS) of the superfused lower oesophageal sphincter from opossum (Monodelphis domestica) elicited biphasic responses. The first phase (relaxation) was strictly dependent on the duration of the EFS. The second phase (contraction) started following termination of the EFS (< or = 15 Hz). EFS at frequencies above 15 Hz led only to contraction, which started immediately upon initiation of the stimulation. 2. In the presence of NG-nitro-L-arginine (L-NOARG; 0.1-300 microM), the relaxation phase was abolished and the contractile response started with the initiation of EFS (at all frequencies) and was greater in magnitude. The contractile response to EFS was completely blocked with scopolamine (10 microM). 3. Exogenous acetylcholine (1-100 microM) elicited concentration-dependent contractions of the sphincter in the presence of botulinum toxin. These contractions were abolished when EFS was applied during administration of acetylcholine. This inhibitory effect of EFS was completely reversed when the tissue was treated with L-NOARG (100 microM). 4. These results suggest that the cholinergic response in the opossum lower oesophageal sphincter is under nitrergic control.     

Effect of metoclopramide, ranitidine, and droperidol on the lower sphincter of the esophagus. Experimental study on the opossum (Didelphis albiventris)

Electromanometric measures of the gastroesophageal junction were performed in 20 adult, male and female, anesthetised opossums. The electromanometric examinations were performed according the intermitent pull through technique. The research was divided in four groups, according to the drug to be analysed: group 1 (20 animals) IM injection of physiological solution (control group); group 2 (20 animals) IM injection of metoclopramide; group 3 (20 animals) IM injection of ranitidine; group 4 (20 animals) IM injection of droperidol. Electromanometry was done 15 minutes before the drug injection, just after the injection and 15, 30, 45 and 60 minutes after the injection. In each one of the moments the pressure of the lower esophageal sphincter (LES-mmHg) was analysed. Considering LES pressure the results observed were: in group 1 it was not observed any significative alteration after IM injection of physiologic solution; in group 2 it was observed significative pressure increase, 15 minutes after metoclopramide IM injection; in group 3 it was observed pressure increase, being significative at 15 and 30 minutes after IM injection; in group 4 it was observed significative increase in LES pressure in every moment, 15 minutes after droperidol IM injection.     

Different protein kinase C isozymes mediate lower esophageal sphincter tone and phasic contraction of esophageal circular smooth muscle

Circular muscle of the esophagus (ESO) is normally relaxed and contracts phasically in response to neural stimuli. In contrast, lower esophageal sphincter (LES) circular muscle maintains spontaneous tone and relaxes in response to neural stimuli. We have previously shown that in vitro, spontaneous LES tone and contraction of ESO in response to acetylcholine (ACh) are antagonized by protein kinase C (PKC) inhibitors, suggesting that PKC activation is responsible for these functions. In the current study, Western blot analysis of LES and ESO revealed PKC-alpha, -betaII, and -gamma isozymes in LES circular muscle, but only PKC-betaII translocated from the cytosolic to the membrane fraction in response to ACh. In contrast, ESO contained PKC-betaII, -gamma, and -epsilon, and only PKC-epsilon translocated to the membrane fraction in response to ACh. In LES single cells isolated by enzymatic digestion and permeabilized by saponin, 1-2-dioctanoylglycerol-mediated contraction was inhibited by preincubation with PKC-betaII antiserum but not by other PKC antisera. In esophageal cells, contraction was inhibited by the PKC-epsilon antiserum but not by antisera against other PKC isozymes. N-Myristoylated peptides derived from the pseudosubstrate sequences of PKC isozymes were used to inhibit saponin, 1-2-dioctanoylglycerol-induced contraction of LES and ESO smooth muscle cells. Contraction of LES cells was reduced by the alpha beta gamma pseudosubstrate but not by the alpha, delta, or epsilon pseudosubstrate. Contraction of ESO cells was reduced by the epsilon pseudosubstrate but not by the alpha, delta, or alpha beta gamma pseudosubstrate. We conclude that different types of contractile activity in the ESO and LES are mediated by different PKC isozymes. LES contraction is mediated by the calcium-dependent PKC-betaII, whereas contraction of ESO is mediated by the calcium-independent PKC-epsilon.     

Effect of hyperparathyroidism and hypercalcemia on lower esophageal sphincter pressure

Heartburn is a frequent and sometimes initial complaint in hyperparathyroidism, and it is often relieved by successful parathyroid surgery. Four of five patients with primary hyperparathyroidism and heartburn obtained relief of symptoms and had an increase in lower esophageal sphincter pressure after successful operative treatment. Four of five volunteers undergoing calcium infusion exhibited a decrease in lower esophageal sphincter pressure after about 2.5 to 3 hours of infusion. Calcium infusion in a treated patient who had an increase in lower esophageal sphincter pressure postoperatively resulted in a transient return of lower esophageal sphincter pressure to preoperative levels.     

Mechanisms and sites of action of endothelins 1 and 2 on the opossum internal anal sphincter smooth muscle tone in vitro

Endothelins, localized in the enteric nervous system, may play important roles in the morphogenesis of the gastrointestinal (GI) tract and in the regulation of GI motility. However, the role of endothelins in the GI sphincters, including the internal anal sphincter (IAS) have not been examined. We examined the actions of endothelins on the basal tone of the opossum IAS circular smooth muscle strips before and after different neurohumoral antagonists or inhibitors. Endothelins 1 and 2 produced a concentration-dependent biphasic effect on the basal tone of the IAS, an initial brief fall followed by a sustained rise. The fall in the IAS smooth muscle tone was not modified by atropine, guanethidine, or tetrodotoxin but was significantly attenuated by the nitric oxide synthase inhibitor L-NNA, the specific neuronal nitric oxide synthase inhibitor, 1-(2-trifluoromethylphenyl)imidazole, the N-type neuronal Ca++-channel blocker omega-conotoxin GVIA, and by the calmodulin antagonist W-13. Endothelin-induced contraction of the IAS, on the other hand, was not affected by any of the neurohumoral antagonists but was significantly inhibited by the selective protein kinase C inhibitor H-7 or the calmodulin inhibitor W-13. The combination of H-7 and W-13 had no additive effect in attenuating the contractile action of endothelin 1. There was clear evidence of a cross-tachyphylaxis to the actions of endothelin 1 and endothelin 2. We conclude that the endothelins exert important neuromodulatory effects on the basal tone of the IAS. The contractile action occurs directly at the smooth muscle and the relaxant action by the activation of neuronal nitric oxide synthase at the nerve terminals. The contraction and relaxation of the smooth muscle caused by endothelins 1 and 2 may involve distinct receptors that are similar for both endothelins. The excitatory actions of endothelin 1 involve both the protein kinase C and the Ca++-calmodulin pathways that may lie in series.     

Effect of gastrin-17 on lower esophageal sphincter characteristics in man

We studied the effect of gastrin-17 on lower esophageal sphincter (LES) characteristics in man. Nine healthy volunteers participated in two experiments performed in random order during continuous infusion of saline (control) or gastrin-17 (15 pmol/kg/hr). LES pressure (LESP) and transient lower esophageal sphincter relaxations (TLESR), as most the important reflux mechanism, were measured with intraesophageal sleeve manometry combined with pH metry. Infusion of gastrin-17 resulted in plasma gastrin levels comparable to those reached after a mixed meal. During continuous gastrin infusion, LESP decreased significantly (P < 0.05) compared to control. The rate and duration of TLESR was not influenced by gastrin-17. Gastroesophageal reflux and the number of TLESR associated with reflux were significantly (P < 0.05) increased during gastrin infusion. These results suggest that in humans gastrin at physiological postprandial plasma concentrations decreases LESP, does not influence TLESR, but increases the percentage of TLESR associated with reflux.     

Effect of morphine on gastroesophageal reflux and transient lower esophageal sphincter relaxation

BACKGROUND: Results from animal studies and preliminary data from pilot studies in patients with primary biliary cirrhosis suggest that tauro-ursodeoxycholic acid has metabolic properties that may favour its long-term use as an alternative to ursodeoxycholic acid for patients with chronic cholestatic liver diseases. No direct comparison of tauro-ursodeoxycholic and ursodeoxycholic acids have yet been carried out in primary biliary cirrhosis. METHODS: The effects of ursodeoxycholic and tauro-ursodeoxycholic acids were compared in 23 patients with primary biliary cirrhosis according to a crossover design. Both drugs were administered at the daily dose of 500 mg. in a randomly assigned sequence for two 6-month periods separated by a 3-month wash-out period. RESULTS: Serum liver enzymes related to cholestasis and cytolysis consistently improved, as compared to baseline values, during the administration of both ursodeoxycholic and tauro-ursodeoxycholic acids, but no significant difference between these two bile acids was found. Both treatments were well tolerated and no patient complained of side effects. CONCLUSION: In the short-term, tauro-ursodeoxycholic acid appears to be safe and at least as effective as ursodeoxycholic acid for the treatment of primary biliary cirrhosis.     

Relationship of cervical and abdominal vagal activity to lower esophageal sphincter function

The purpose of this study was to compare the effects of electrical stimulation of the abdominal and cervical portions of the vagus on lower esophageal sphincter (LES) pressure in the anesthetized opossum. Unilateral or bilateral abdominal vagotomy gave no significant change in basal LES pressure or in the sphincteric response to swallowing. Electrical stimulation of the peripheral end of the sectioned cervical vagus gave a frequency-related decrease in LES pressure with a maximum reduction of 93.5 +/- 2.5% at 10 HZ, 10 V. Stimulation of the central end of the cervical vagus increased LES pressure, with a maximum response of 34.0 +/- 1.9 mm Hg. Neither peripheral nor central stimulation of the sectioned abdominal vagus had significant effect on LES pressure (P greater than 0.05). Additionally, LES relaxation in response to swallowing or cervical vagal stimulation was intact after bilateral abdominal vagotomy. These studies suggest that whereas the cervical portion of the vagus mediates inhibitory and excitatory changes in LES pressure, the abdominal vagus has no demonstrable role in the control of LES function.     

Lower sphincter of the opossum esophagus in pseudopregnancy

To seek a possible role of estrogen and progesterone in the development of changes in esophageal function during pregnancy, we produced a state of pseudopregnancy by administration of hormones to a suitable animal model. Twenty-two female opossums weighing an average of 2.5 kg, were divided into two groups. The treated group received intramuscular injections of 100 microgram of estradiol valerate daily from day 1 to day 12 and 15 mg of medroxyprogesterone acetate from day 7 to day 12. The control group received no injections. Both groups underwent manometry on days 1, 7, and 12. Lower esophageal sphincter pressure decreased (P less than 0.05) in treated animals from 58 +/- 13 mm Hg and 57 +/- 11 on days 1 and 7, respectively, to 44 +/- 10 mm Hg on day 12. The lower esophageal sphincter pressure remained unchanged in control animals. In both groups, there was no change in peristaltic wave pressure, duration, or velocity in the distal 6 cm of the esophagus. No abnormal peristaltic phenomena were observed. Esophageal muscle strips prepared from treated animals showed responses to electrical field stimulation of intrinsic nerves that were like those from control animals. The same was true for responses to acetylcholine and pentagastrin. Total tissue water and total tissue potassium content did not differ in treatment and control animals.     

Endogenous motilin and lower esophageal sphincter pressure in man: clue to an association

In man (n = 5), after intraduodenal instillation of 50 ml of 0.1 N hydrochloric acid the lower esophageal sphincter pressure (LESP) and plasma motilin concentrations rise concomitantly exceeding basal by about 80% (p less than 0.025) and 90% (p less than 0.05), respectively, at 3 to 4 minutes. These results suggest that the increase in LESP after duodenal acidification may be brought about by endogenously released motilin.     

Simultaneous study of tones of the lower esophageal sphincter and proximal stomach in healthy humans

OBJECTIVES: The aim of this study was to determine the feasibility and tolerance of simultaneous assessment of the proximal gastric and lower esophageal sphincter tones in healthy humans, in fasting and fed conditions. METHODS: Esophageal motility and lower esophageal sphincter tone were measured on two separate days in 7 healthy subjects. During one of these sessions, proximal gastric tone was simultaneously assessed with a balloon placed in the proximal stomach and connected to an electronic barostat. Motility was monitored 1 hour before and 4 hours after a liquid fat meal (400 mL/600 kcal). In four other healthy subjects, simultaneous assessment of proximal gastric and lower esophageal sphincter tones was performed after, suggestion of a 200 mL/200 kcal liquid meal. RESULTS: Simultaneous use of gastric barostat and esophageal motility device was well tolerated in 10/11 healthy subjects. The presence of the barostat balloon did not significantly affect basal lower esophageal sphincter tone and the rate of transient lower esophageal sphincter relaxations. The important fall of lower esophageal sphincter basal tone after ingestion of the 400 mL/600 kcal meal did not allow to detect a post-prandial increase of transient lower esophageal sphincter; relaxations. After ingestion of the 200 mL/200 kcal meal, the incidence of transient lower esophageal sphincter relaxations increased (p < 0.02 vs. fasting). Maximal gastric relaxation was reached 15 min after meal, and appeared shorter (112 +/- 17 min vs. 167 +/- 24 min) and more pronounced (292 +/- 26 mL vs. 190 +/- 51 mL) than after the 400 mL meal, but differences were not statistically significant. CONCLUSIONS: Simultaneous assessment of proximal gastric and lower esophageal sphincter tone is feasible, after oval ingestion of a meal. Since the 400 mL meal induces in important inhibition of lower esophageal sphincter basal tone, the 200 mL meal seems more adequate for assessment of the transient lower esophageal sphincter relaxations.     

Static and dynamic function of the lower esophageal sphincter before and after laparoscopic Nissen fundoplication

SUBJECT: We analysed the periprosthetic bone mineral density (BMD) in a prospective longitudinal study over two years after operation and in a separate cross-sectional study more than five years after implantation of cementless total hip arthroplasty (CLS-stem, Mecron threaded acetabular cup) by using dual-energy X-ray absorptiometry (DEXA). MATERIALS AND METHODS: In n = 53 patients (29 women, 24 men) we analysed the periprosthetic BMD prospectively in certain periods. All patients had an uncomplicated postoperative course and good clinical outcome (Merle d'Aubigne score > 12). In the cross-sectional study we analysed 23 patients (13 women, 10 men). Regions of Interest (ROI) were defined according to Gruen et al. for the periprosthetic femur and to De Lee and Charnley for the periprosthetic acetabulum. RESULTS: BMD significantly decreases in the periprosthetic femur as well as in the periprosthetic acetabulum during the first three months. In men BMD reaches its lowest values between six months (femur) and one year (acetabulum) after operation and then increases to 96.2% at the femur and 93.8% at the acetabulum. In women BMD decreases during the entire follow-up to 89.4% at the periprosthetic femur and 80.0% at the periprosthetic acetabulum. In the proximal zones 1 and 7 of the femur and the cranial-medial zone II of the acetabulum we observed the highest decrease of mineralisation. More than five years after implantation of the prosthesis BMD in the femur showed only little changes. On the other side BMD around the threaded acetabular cup significantly decreased to 67.4% in women and 79.1% in men. CONCLUSION: The results reflect the different stress on the periprosthetic bone after implantation of the prosthesis and fit to earlier reported good clinical results of the CLS-stem and to increased loosening rate of threaded acetabular cups after five years. Analysing changes of mineralisation in cementless total hip arthroplasty DEXA together with the analization scheme according to Gruen at the femur and to De Lee and Charnley at the acetabulum is a useful method and has been reliable in clinical practise.     

Transdiaphragmatic pressure gradients and the lower esophageal sphincter after tight abdominal wall plication in the rat

BACKGROUND: Gastroesophageal reflux (GER) is increasingly recognized as a complication of surgical closure of gastroschisis and omphalocele. AIM: This study tests the hypothesis that forceful abdominal wall closure reinforces the transdiaphragmatic pressure gradients that constitute the main GER-driving force and challenges the antireflux barrier. MATERIALS AND METHODS: Abdominal and esophageal pressures as well as lower esophageal sphincter pressures (LESP) and length (LESL) were measured in 17 adult rats before tight abdominal wall plication, after it, and 1 week later. RESULTS: This maneuver increased the transdiaphragmatic expiratory gradient from 0.67 +/- 1.31 to 6.97 +/- 2.68 mm Hg (P < .01) and the inspiratory gradient from 4.36 +/- 1.13 to 10.79 +/- 2.31 mm Hg (P < .01) by markedly increasing both the expiratory (from 1.47 +/- 0.74 to 9.44 +/- 1.85 mm Hg; P < .01) and inspiratory (from 0.98 +/- 0.69 to 6.83 +/- 1.55 mm Hg; P < .01) intraabdominal pressures. These changes were transient, and all pressures became normal after 1 week. The antireflux barrier functioned properly under these new conditions because both LESP and the diaphragmatic pinch-cock pressure (DPP) increased, from 20.3 +/- 3.63 to 26.5 +/- 4.31 mm Hg (P < .01) and from 16.4 +/- 7.25 to 22.5 +/- 4.36 mm Hg (P < .01), respectively, while LESL remained unchanged. CONCLUSION: Tight abdominal wall plication in the rat generates high intraabdominal pressures and thus reinforces the transdiaphragmatic pressure gradients, but these conditions elicit a healthy barrier response with sphincteric reinforcement. In addition, these changes are transient and fade out some time after operation. These facts should be taken into account for understanding the pathogenesis of GER after repair of abdominal wall defects in human babies.