Measuring esophageal distension by high-frequency intraluminal ultrasound probe

Distension of the esophagus can cause heartburn and chest pain; however, none of the available techniques to study the esophagus measure esophageal distension. We evaluated the technique of high-frequency intraluminal ultrasound probe (HFIUS) to measure the esophageal cross-sectional area (CSA) during gastroesophageal reflux (GER). The following methods were used: 1) the CSA of agarose gel tubes of known dimensions were measured using ultrasound probes; 2) seven normal subjects were studied to evaluate the esophageal CSA during different bolus volumes (1, 5, 10, 15, and 20 ml) of water swallows (WS); and 3) simultaneous pressures, pH, and ultrasound images of the esophagus were recorded in healthy subjects. In vitro studies showed that the HFIUS measured the CSA of the tubes accurately. The maximal CSA of the distal esophagus during WS with boluses of 1, 5, 10, 15, and 20 ml were 54, 101, 175, 235, and 246 mm(2), respectively. Esophageal contents during 62 episodes of transient lower esophageal sphincter relaxations, 29 pH positive, and 33 pH negative GER episodes revealed that reflux of air into the esophagus occurred more frequently than liquid. The median CSA and estimated diameter of the esophagus during liquid GER was 44.1 mm(2) and 7.5 mm, respectively. We conclude that HFIUS is a valid technique to measure the CSA of the esophagus in vivo during GER. Distension of the esophagus during physiological GER is relatively small.     

Rectal and colonic distension elicit viscerovisceral reflexes in humans

Colonic transit is slowed in patients with disordered rectal evacuation, but the mechanism of this phenomenon is unclear. Our objective was to investigate rectocolonic inhibitory reflexes in humans to provide potential insight into patients with obstructed defecation. In 30 healthy subjects, a barostat-manometric assembly recorded colonic tone and phasic activity in the descending colon during rectal distension and recorded rectal tone during colonic distension. Phasic distensions were 8, 16, and 32 mmHg above balloon operating pressure, and staircase inflations were comprised of balloon inflation then deflation in 2-mmHg increments at 30-s intervals from 0 to 36 mmHg. Colonic balloon volumes increased to a similar extent during phasic rectal distensions 8, 16, and 32 mmHg above operating pressure, reflecting reduced colonic tone; balloon volumes also increased and phasic pressure activity decreased during staircase rectal distensions. In contrast, rectal balloon volume declined, reflecting increased tone during phasic and staircase colonic distensions. Thus rectal distension inhibited colonic motor activity, indicative of a viscerovisceral inhibitory reflex.     

Atrial distension in humans during weightlessness induced by parabolic flights

Central venous pressure, esophageal pressure, and left atrial diameter were measured in individuals during each stage of parabolic flight, with emphasis on weightlessness. Results indicated that short periods of weightlessness lead to an increase in transmural central venous pressure and left atrial diameter, although there is a decrease in central venous pressure.     

Cholecystokinin pathways modulate sensations induced by gastric distension in humans

Ingested fat releases CCK, causes gastric relaxation, delays gastric emptying, and limits meal size; however, the mechanistic link among these actions has not been established. Fatty acid release of CCK is chain-length sensitive; dodecanoic acid (C12) induces greater CCK release than decanoic acid (C10). The effect of C12 or C10 on tolerance to subsequent intragastric infusion of liquid was determined in healthy subjects, with and without the CCK(1) receptor antagonist dexloxiglumide. Gastric wall relaxation after either fatty acid was assessed by graded volume distension and by barostat; gastric emptying was measured by gastric aspiration and by a [(13)C]octanoic acid breath technique. C12 released more CCK (mean plasma CCK after vehicle, 4.7 +/- 0.8 pM; C10, 4.8 +/- 0.3 pM; C12, 8 +/- 1.2 pM; P < 0.05 C12 vs. C10 or vehicle) and reduced the volume of water (and of 5 and 25% glucose solutions) delivered at maximum tolerance compared with C10 or vehicle (volume of water tolerated after vehicle, 1,535 +/- 164 ml; C10, 1,335 +/- 160 ml; C12, 842 +/- 103 ml; P < 0.05 C12 vs. C10 or vehicle); this effect was abolished by dexloxiglumide. Intragastric volumes were always similar at the limit of tolerance, and, whereas gastric relaxation occurred to similar degrees after the fatty acids, its duration was longer after C12, which also induced a longer delay in half-gastric emptying [t(1/2)(min) after vehicle, 53 +/- 2; C10, 67 +/- 3; C12, 88 +/- 7; P < 0.05 C12 vs. C10 or vehicle]. In conclusion, ingestion of a CCK-releasing fatty acid reduces the tolerated volume of liquid delivered into the stomach, primarily via a CCK(1) receptor-mediated delay in gastric emptying.     

Effect of phentolamine on carotid reflexes induced by acetylcholine

Acetylcholine was injected into the common carotid artery of 15 mongrel dogs. In the animals with tied internal carotid artery, hyperpnoea, bradycardia and hypotension was observed, and in the animals with free internal carotid artery the hyperphoea was followed by apnoea. The administration of phentolamine provokes a temporary decrease or abolition of the reflexes produced by acetylcholine. This action of the alpha-blocker is due to a local effect because when phentolamine is injected intravenously it does not happen and the reflexes produced by acetylcholine with starting place at the carotid sinus of the opposite side are not affected.     

Crural diaphragm inhibition during esophageal distension correlates with contraction of the esophageal longitudinal muscle in cats

Esophageal distension causes simultaneous relaxation of the lower esophageal sphincter (LES) and crural diaphragm. The mechanism of crural diaphragm relaxation during esophageal distension is not well understood. We studied the motion of crural and costal diaphragm along with the motion of the distal esophagus during esophageal distension-induced relaxation of the LES and crural diaphragm. Wire electrodes were surgically implanted into the crural and costal diaphragm in five cats. In two additional cats, radiopaque markers were also sutured into the outer wall of the distal esophagus to monitor esophageal shortening. Under light anesthesia, animals were placed on an X-ray fluoroscope to monitor the motion of the diaphragm and the distal esophagus by tracking the radiopaque markers. Crural and costal diaphragm electromyograms (EMGs) were recorded along with the esophageal, LES, and gastric pressures. A 2-cm balloon placed 5 cm above the LES was used for esophageal distension. Effects of baclofen, a GABA(B) agonist, were also studied. Esophageal distension induced LES relaxation and selective inhibition of the crural diaphragm EMG. The crural diaphragm moved in a craniocaudal direction with expiration and inspiration, respectively. Esophageal distension-induced inhibition of the crural EMG was associated with sustained cranial motion of the crural diaphragm and esophagus. Baclofen blocked distension-induced LES relaxation and crural diaphragm EMG inhibition along with the cranial motion of the crural diaphragm and the distal esophagus. There is a close temporal correlation between esophageal distension-mediated LES relaxation and crural diaphragm inhibition with the sustained cranial motion of the crural diaphragm. Stretch caused by the longitudinal muscle contraction of the esophagus during distension of the esophagus may be important in causing LES relaxation and crural diaphragm inhibition.     

Baclofen blocks LES relaxation and crural diaphragm inhibition by esophageal and gastric distension in cats

Esophageal distension and transient lower esophageal sphincter (LES) relaxation (TLESR) are accompanied by simultaneous relaxation of the LES and inhibition of crural diaphragm. Recent studies indicate that baclofen decreases the frequency of TLESR; however, its effect on the crural diaphragm is not known. We evaluated the effects of baclofen on LES relaxation and crural diaphragm inhibition induced by gastric distension and esophageal distension in cats. Five adult cats underwent surgical implantation of wire electrodes into the crural and costal diaphragm for measurement of their EMG activity, respectively. One week after the surgery, animals were lightly sedated and recordings were performed using a manometry catheter equipped with a 2.5-cm balloon. The effects of baclofen (10 micromol/kg iv) on the graded esophageal distension and gastric distension-induced LES and crural diaphragm responses were studied. Distension of the esophagus and stomach induces relaxation of the LES and inhibition of the crural diaphragm, simultaneously. Baclofen blocks both the esophageal and the gastric distension-induced relaxation of the LES and inhibition of the crural diaphragm. The magnitude of response to baclofen was significantly larger for the crural diaphragm inhibition than for the LES relaxation. Baclofen, a GABA(B) receptor agonist, blocks the reflex inhibitory pathway to the LES and crural diaphragm. The reflex inhibitory pathway to the crural diaphragm is more sensitive to blockade by baclofen than the reflex LES inhibitory pathway.     

Mechanisms of the haematological changes induced by hyperventilation

During voluntary hyperventilation an increase in the lymphocyte and thrombocyte counts occurs, paralleled by an increase in plasma epinephrine and norepinephrine. All these changes are rapidly reversible after hyperventilation and are followed by an increase in the neutrophil granulocyte count. The pathophysiological mechanisms of these changes were investigated by comparison of the hyperventilation-induced changes of the blood picture in 11 normal, 9 splenectomized and 12 beta-blocked volunteers. Splenectomy did not affect the hyperventilation-induced mobilization of lymphocytes and neutrophils but totally suppressed the change in the thrombocyte count. beta-blockade by 80 mg propranolol did not suppress the hyperventilation-induced increase in neutrophils. It reduced the absolute increase of lymphocytes and thrombocytes by half, but it also increased the baseline counts of these cells. The study shows that hyperventilation mobilizes thrombocytes from the spleen but not from extralienal pools, and that lymphocytes and neutrophils are mobilized from extralienal pools. Whereas neutrophil mobilization is not suppressed by beta-blockade, the reduction of hyperventilation-induced mobilization of lymphocytes and thrombocytes may be due to a reduction in the size of the mobilizable cell pools, and therefore cannot be interpreted as a sure indication that adrenergic mechanisms are involved in their hyperventilation-induced mobilization.     

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.     

Sensory peptide neurotransmitters mediating mucosal and distension evoked neural vasodilator reflexes in guinea pig ileum

The aim was to determine the role CGRP and/or tachykinins released from sensory neural mechanisms in enteric neural vasodilator pathways. These pathways project through the myenteric plexus to submucosal vasodilator neurons. Submucosal arterioles were exposed in the distal portion of an in vitro combined submucosal-myenteric guinea pig ileal preparation, and dilation was monitored with videomicroscopy. Vasodilator neural reflexes were activated by gently stroking the mucosa with a fine brush or by distending a balloon placed beneath the flat-sheet preparation in the proximal portion. Dilations evoked by mucosal stroking were inhibited 64% by the CGRP 8-37 and 37% by NK3 (SR 142801) antagonists. When the two antagonists were combined with hexamethonium, only a small vasodilation persisted. Balloon distension-evoked vasodilations were inhibited by NK3 antagonists (66%) but were not altered by CGRP 8-37. In preparations in which myenteric descending interneurons were directly activated by electrical stimulation, combined application of CGRP 8-37 and the NK antagonists had no effect. Stimulation of capsaicin sensitive nerves in the myenteric plexus did not activate these vasodilator reflexes. These findings suggest that mucosal-activated reflexes result from the release of CGRP and tachykinins from enteric sensory neurons. Distension-evoked responses were significantly blocked by NK3 antagonists, suggesting that stretch activation of myenteric sensory neurons release tachykinins that activate NK3 receptors on myenteric vasodilator pathways.     

Mechanisms of esophageal cancer development in Brazilians

Esophageal cancer represents one of the most common and lethal cancers around the World. Some areas of South America, including parts of Brazil, present the highest incidence of the disease in the West. The main etiological factors that have been associated with the disease in Brazil are alcohol consumption, tobacco smoking and, in the South, consumption of hot maté. Nitrosamines are the only carcinogens capable of inducing tumors in the esophagus of experimental animals, with the rat being the most susceptible species, mainly due to tissue specific metabolic activation by CYP enzymes. Studies of CYP2A expression in the esophagus of rodents suggest an association between CYP2A expression and esophageal susceptibility to tumor induction. CYP2A6 and CYP2E1, the main enzymes to activate nitrosamines in humans, are the only carcinogen activating CYP enzymes to be expressed in the esophagus of Brazilians. Patients who presented high levels of CYP2A6 expression could activate nitrosamines at rates comparable to the rat. This expression profile is different from those present in French patients. We investigated 34 Brazilian patients regarding the risk associated with polymorphisms in drug metabolizing enzymes and TP53 mutations. A GSTP1 polymorphism presented a clear risk to white and non-white patients to develop esophageal cancer. GSTM1 null polymorphism also seemed to be associated with an increased risk. CYP2A6, CYP2E1, SOD2, and GSTT1 polymorphisms were not associated with an increased risk of esophageal cancer. TP53 mutations occurred mostly in exon 7, differing from the mutation profile found in the IARC database. The preliminary results obtained with polymorphisms of drug metabolizing enzymes and TP53 mutations need to be confirmed in a larger number of samples in order to compare the mechanisms of esophageal cancer development in Brazilians with that of other populations.     

Mechanisms of cardiac fibrosis induced by urokinase plasminogen activator

Human hearts with end-stage failure and fibrosis have macrophage accumulation and elevated plasminogen activator activity. However, the mechanisms that link macrophage accumulation and plasminogen activator activity with cardiac fibrosis are unclear. We previously reported that mice with macrophage-targeted overexpression of urokinase plasminogen activator (SR-uPA+/o mice) develop cardiac macrophage accumulation by 5 weeks of age and cardiac fibrosis by 15 weeks. We used SR-uPA+/o mice to investigate mechanisms through which macrophage-expressed uPA causes cardiac macrophage accumulation and fibrosis. We hypothesized that: 1) macrophage accumulation and cardiac fibrosis in SR-uPA+/o mice are dependent on localization of uPA by the uPA receptor (uPAR); 2) activation of plasminogen by uPA and subsequent activation of transforming growth factor-beta1 (TGF-beta1) and matrix metalloproteinase (MMP)-2 and -9 by plasmin are critical pathways through which uPA-expressing macrophages accumulate in the heart and cause fibrosis; and 3) uPA-induced cardiac fibrosis can be attenuated by treatment with verapamil. To test these hypotheses, we bred the SR-uPA+/o transgene into mice deficient in either uPAR or plasminogen and measured cardiac macrophage accumulation and fibrosis. We also measured cardiac TGF-beta1 protein (total and active), Smad2 phosphorylation, and MMP activity after the onset of macrophage accumulation but before the onset of cardiac fibrosis. Finally, we treated mice with verapamil. Our studies revealed that plasminogen is necessary for uPA-induced cardiac fibrosis and macrophage accumulation but uPAR is not. We did not detect plasmin-mediated activation of TGF-beta1, MMP-2, or MMP-9 in hearts of SR-uPA+/o mice. However, verapamil treatment significantly attenuated both cardiac fibrosis and macrophage accumulation.     

Mechanisms of leukocyte-mediated tissue injury induced by interleukin-2

In this review we discuss the effects of interleukin-2 (IL-2) therapy on trafficking of leukocytes and platelets to normal organs. The use of animal models has allowed the elucidation of events leading to damage and/or dysfunction of normal tissues after IL-2 administration. These studies have shown that acute toxicity induced by IL-2 is mediated primarily by neutrophils. Chronic toxicity results from the adhesion and transmigration of activated lymphocytes into normal organs. Platelet-derived microvascular thrombosis also contributes to the vascular toxicity of IL-2. A better understanding of these mechanisms may lead to the development of interventions that will significantly improve the therapeutic efficacy of IL-2. Received: 22 August 1998 / Accepted: 16 October 1998     

Mechanisms of polyclonal tolerance induced by lipopolysaccharide and cyclophosphamide

The treatment of recipient mice with LPS from S. marcescens followed by the injection of CY 48 h later inhibited a subsequent antibody production against unrelated antigen (SRBC) and polyclonal mitogen (LPS from Br. abortus). Such a reactivity persisted for 2-3 weeks after treatment. It was shown that the number of Ig+ cells in the spleens of treated mice was decreased, while the population of spleen Thy-1.2+ cells remained unaltered. Cell-cooperative test revealed that the function of B cells, but not T cells, was inhibited by the treatment. There were no changes in DTH response to SRBC. Thus, a subsequent treatment of mice with LPS and CY led to B-cell deficiency. The nature of this phenomenon is presumably the same as the nature of CY-induced antigen-specific immunological tolerance.