Biomedical subjects

R C Orlando

Publications and source records attributed to R C Orlando.

At least 19 recordsLinked to original sources

PubMed2006

Effect of luminal acidity on the apical cation channel in rabbit esophageal epithelium.

Esophageal epithelial cells contain an apical cation channel that actively absorbs sodium ions (Na(+)). Since these channels are exposed in vivo to acid reflux, we sought the impact of high acidity on Na(+) channel function in Ussing-chambered rabbit epithelium. Serosal nystatin abolished short-circuit current (I(sc)) and luminal pH titrated from pH 7.0 to pH > or = 2.0 had no effect on I(sc). Circuit analysis at pH 2.0 showed small, but significant, increases in apical and shunt resistances. At pH < 2.0, I(sc) increased whereas resistance (R(T)) decreased along with an increase in fluorescein flux. The change in I(sc), but not R(T), was reversible at pH 7.4. Reducing pH from 7.0 to 1.1 with H(2)SO(4) gave a similar pattern but higher I(sc) values, suggesting shunt permselectivity. A 10:1 Na(+) gradient after nystatin increased I(sc) by approximately 4 muAmps/cm(2) and this declined at pH < or = 3.5 until it reached approximately 0.0 at pH 2.0. Impedance analysis on acid-exposed (non-nystatin treated) tissues showed compensatory changes in apical (increase) and basolateral (decrease) resistance at modest luminal acidity that were poorly reversible at pH 2.0 and associated with declines in capacitance, a reflection of lower apical membrane area. In esophageal epithelium apical cation channels transport Na(+) at gradients as low as 10:1 but do not transport H(+) at gradients of 100,000:1 (luminal pH 2.0). Luminal acid also inhibits Na(+) transport via the channels and abolishes it at pH 2.0. These effects on the channel may serve as a protective function for esophageal epithelium exposed to acid reflux.

Acids↗

PubMed2004

Calcium-switch technique and junctional permeability in native rabbit esophageal epithelium.

The Ca(2+)-switch technique was used to investigate the nature of the barrier governing (paracellular) permeability across the junctions of "native" rabbit esophageal epithelium. This was done by mounting esophageal epithelium in Ussing chambers to monitor transepithelial electrical resistance (R(T)), a marker of junctional permeability. When exposed to Ca(2+)-free Ringer solutions containing EDTA, R(T) declined approximately 35% below baseline over 2 h, and this decline reversed within 2 h by restoration of (1.2 mM) Ca(2+)-containing, normal Ringer solution ("Ca(2+)-switch technique"). Junctional resealing, i.e., increased R(T) on Ca(2+) replacement, was assessed by the Ca(2+)-switch technique and shown to be 1) specific for Ca(2+), with only Mn(2+) among substituted divalent cations yielding partial resealing; 2) a function of extracellular Ca(2+) levels because maneuvers (BAPTA/AM or A23187 exposure) to alter intracellular Ca(2+) had no effect; 3) dose dependent, requiring as a minimum > or =0.5 mM Ca(2+) and 1.2 mM Ca(2+) for optimization; and 4) independent of protein synthesis because it was not inhibited by cycloheximide. Resealing was also inhibited by luminal antibodies or synthetic peptides to the extracellular domain of E-cadherin. Immunohistochemistry revealed E-cadherin within all layers of stratum corneum in Ca(2+)-free but not Ca(2+)-containing solution. The present investigation documents, using the Ca(2+)-switch technique, that esophageal epithelial junctions contain a major Ca(2+)-dependent component and that this component reflects adhesion between the extracellular domains of E-cadherin containing a histidine-alanine-valine recognition sequence.

Alanine↗

PubMed2004

Dilated intercellular spaces and shunt permeability in nonerosive acid-damaged esophageal epithelium.

OBJECTIVES: It has recently been established that patients with nonerosive reflux disease have on biopsy within esophageal epithelium a lesion known as dilated intercellular spaces (DIS). METHODS: To further explore the nature and implications of this lesion, in vitro models of nonerosive acid and acid-pepsin damage were created in Ussing chamber-mounted rabbit esophageal epithelium. Using these models circuit analysis and permeability studies were carried out, the latter using dextran of varying size and human epidermal growth factor (EGF). RESULTS: Luminal HCl, pH 1.1, or HCl, pH 2.0 + pepsin, 1 mg/ml, for 30 min significantly reduced transepithelial electrical resistance (RT) but produced no gross erosions or histologic evidence of cell necrosis. Transmission electron microscopy, however, documented the presence of DIS. Circuit analysis on healthy esophageal epithelium showed that shunt resistance (RS) was much lower than apical membrane, basolateral membrane and transcellular resistances (Ra, Rb, and Rcell, respectively) and approached that of RT. Further, circuit analysis on acid and acid-pepsin damaged tissues showed that the declines in RT resulted from declines in RS. Moreover, the declines in RT (and so RS) were associated with a linear increase in permeability to 4 kD dextrans as well as an increase in permeability to 6 kD EGF and dextrans as large as 20 kD. CONCLUSIONS: In nonerosive acid-damaged esophageal epithelium DIS develop in association with and as a marker of reduced transepithelial resistance and increased shunt permeability. This change in shunt permeability upon acid or acid-pepsin exposure is substantial, permitting dextran molecules as large as 20 kD (33 A) to diffuse across the epithelium. Also, this shunt leak enables luminal EGF at 6 kD to diffuse across the acid-damaged epithelium and by so doing enables it to access its receptors on epithelial basal cells. We hypothesize that the shunt leak of EGF may in part account for the development of a reparative phenomenon on esophageal biopsy in patients with nonerosive reflux disease known as basal cell hyperplasia.

Animals↗

PubMed2004

Review article: the pathophysiology of gastro-oesophageal reflux disease - oesophageal manifestations.

The pathogenesis of gastro-oesophageal reflux disease (GERD) is multifactorial, involving transient lower oesophageal sphincter relaxations (TLESRs) as well as other lower oesophageal sphincter (LES) pressure abnormalities. GERD is associated with a decrease in LES pressure, which can be provoked by factors such as foods (fat, chocolate, etc.), alcohol, smoking and medications. These factors have also been shown to increase TLESRs. As a result, reflux of acid, bile, pepsin and pancreatic enzymes occurs, leading to oesophageal mucosal injury, which can potentially progress to oesophageal adenocarcinoma in a minority of patients with Barrett's metaplasia. In addition, duodenogastric contents can also contribute to oesophageal injury. Other factors contributing to the pathophysiology of GERD include hiatal hernia, poor oesophageal clearance, delayed gastric emptying and impaired mucosal defensive factors. Hiatal hernia has a permissive role in the pathogenesis of reflux oesophagitis by promoting LES dysfunction. Delayed gastric emptying, resulting in gastric distension, can significantly increase the rate of TLESRs, contributing to postprandial GER. The mucosal defensive factors have an important role in GERD. When excessive acid causes a breakdown in oesophageal epithelial defenses, epithelial resistance may be reduced. Nocturnal GERD is associated with prolonged acid exposure and proximal extent of acid contact, which elevates the risk for oesophageal damage and GERD-related complications. In sum, GERD is a complex problem caused by many factors that are exacerbated when the patient is in the supine position.

Esophageal Sphincter, Lower↗

PubMed2002

Physiological and morphological effects of alendronate on rabbit esophageal epithelium.

Alendronate, an aminobisphosphonate, produces as a side effect a topical (pill induced) esophagitis. To gain insight into this phenomenon, we assessed the effects of luminal alendronate on both esophageal epithelial structure and function. Sections of rabbit esophageal epithelium were exposed to luminal alendronate at neutral or acidic pH while mounted in Ussing chambers to monitor transmural electrical potential difference (PD), short-circuit current (I(sc)), and resistance (R). Morphological changes were sought by light microscopy in hematoxylin and eosin-stained sections. Impedance analysis was used for localization of alendronate-induced effects on ion transport. Luminal, but not serosal, alendronate (pH 6.9-7.2), increased PD and I(sc) in a dose- and time-dependent manner, with little change in R and mild edema of surface cell layers. The changes in I(sc) (and PD) were reversible with drug washout and could be prevented either by inhibition of Na,K-ATPase activity with serosal ouabain or by inhibition of apical Na channels with luminal acidification to pH 2.0 with HCl. An effect on apical Na channel activity was also supported by impedance analysis. Luminal alendronate at acidic pH was more damaging than either alendronate at neutral pH or acidic pH alone. These data suggest that alendronate stimulates net ion (Na) transport in esophageal epithelium by increasing apical membrane sodium channel activity and that this occurs with limited morphological change and no alteration in barrier function. Also alendronate is far more damaging at acidic than at neutral pH, suggesting its association with esophagitis requires gastric acid for expression. This expression may occur either by potentiation between the damaging effects of (refluxed) gastric acid and drug or by acid-induced conversion of the drug to a more toxic form.

Alendronate↗

PubMed2001

Overview of the mechanisms of gastroesophageal reflux.

Reflux of acidic gastric contents through the esophagogastric junction into the esophageal lumen occurs in everyone nearly every day. The esophagogastric junction is composed of several structural components that contribute to its function as the primary antireflux barrier. Only when 1 or more of these components fail does reflux esophagitis develop. The initial focus of this review is on transient lower esophageal sphincter relaxations, a vagally mediated reflex arc that accounts for almost all reflux events in healthy individuals and the majority of reflux events in those with reflux esophagitis. The association of erosive esophagitis with low or absent (incompetent) lower esophageal sphincter (LES) pressure and anatomic disruptions of the esophagogastric junction, such as hiatal hernia, are also important, especially with respect to whether the LES dysfunction and hernia are the cause or the consequence of erosive disease.

Disease Progression↗

PubMed2001

Gastroesophageal reflux disease.

Gastroesophageal reflux disease (GERD) is a chronic disorder that affects millions of people worldwide and has the potential to lead to serious consequences, including cancer of the esophagus. It for this reason that there is such intense interest in the topic, this emphasized by the identification of some 341 articles published in the English language in the year 2000 alone. The present report highlights the results of a number of studies that either increase our understanding of the condition or raise important issues about its diagnosis and treatment. Included in the areas covered are (1) the role of genetics in GERD; (2) the mechanism for transient lower esophageal sphincter relaxations and their association with hiatal hernias; (3) the role of Helicobacter pylori in GERD and Barrett esophagus; (4) efficacy and safety of proton pump inhibitors in GERD; and (5) the mechanism for chronic cough in patients with GERD, among others.

Journal Article↗

PubMed2001

The role of pepsin in acid injury to esophageal epithelium.

OBJECTIVES: The development of reflux esophagitis in humans is a process resulting from esophageal exposure to refluxed gastric contents. There is no doubt that damage to the esophageal epithelium requires exposure to gastric acid; however, the role of refluxed pepsin as contributor to this damage seems to be underappreciated. METHODS: The role of physiological concentrations of pepsin was examined in Ussing chambered rabbit esophageal epithelium and in cultured esophageal epithelial cells. RESULTS: The results of this investigation reaffirmed the ability of pepsin to increase the rate and degree of esophageal cell and tissue damage at acidic pH, although the range of activity was limited to pH < 3.0. Moreover, the increased rate of tissue damage by acidified pepsin rapidly (within 15 min) produced a lesion that was irreversible, whereas, in a similar time frame, acid alone produced a lesion that was completely reversible. This early lesion by acidified pepsin was localized by performance of mannitol fluxes in apparently undamaged esophageal epithelium on light microscopy to the intercellular junctional complex. Further acid produced similar degrees of cell killing as acidified pepsin at pH < 3.0 in rabbit esophageal epithelial cells in suspension but not when growing on coverslips or present within intact epithelium. CONCLUSIONS: These studies suggest that acidified pepsin plays a key role in the development of reflux esophagitis by producing an early irreversible lesion that results in an increase in paracellular permeability, which indirect evidence suggests is due to damage to the junctional complex. The irreversibility of the increase in paracellular permeability is likely to aid conversion of nonerosive to erosive damage to the epithelium by permitting luminal acid greater access to the basolateral membrane of esophageal epithelial cells, which is known to be acid permeable.

Animals↗

PubMed2000

Mechanisms of reflux-induced epithelial injuries in the esophagus.

The esophagus is lined by a moist stratified squamous epithelium. In humans, this epithelium, as evidenced by the Bernstein test, has considerable capacity to resist damage even upon direct contact of high concentrations of luminal acid. This intrinsic property of the epithelium to defend itself against luminal acid is called "tissue resistance." Tissue resistance is comprised of a number of important structures and functions, the individual functions of which are described in this review. Moreover, when luminal acidity is sufficiently noxious, tissue resistance can be overcome, leading to heartburn and ultimately cell necrosis. Herein are described the mechanisms by which acid overcomes the epithelial defense to produce these typical signs and symptoms of gastroesophageal reflux disease.

Endothelium↗

PubMed2000

Eicosanoids and the esophagus.

Eicosanoids are products of arachidonic acid metabolism. Among the products produced are the prostaglandins and leukotrienes, products which are known to play important roles in health and disease of many gastrointestinal tissues. Here, we review current knowledge about eicosanoids in the esophagus, including production in healthy and diseased tissues and potential physiologic and pathophysiologic effects in two important esophageal mucosal disorders, reflux esophagitis and esophageal cancer.

Animals↗

PubMed2000

Gastroesophageal reflux disease.

Gastroesophageal reflux disease (GERD) is a common chronic disorder affecting millions of people worldwide. This is a review of a number of published studies in the past year that increase current understanding or raise important issues about this disorder. Among the areas covered are the epidemiology and role of genetics in GERD; its pathogenesis with respect to duodenogastric reflux and impaired epithelial barrier function; the effects of atropine on transient lower esophageal sphincter relaxations; the role of acid suppression, heat shock proteins, and the enzyme cyclooxygenase-2 in Barrett esophagus and esophageal adenocarcinoma; the complication rates in laparoscopic fundoplication; and the results of ablation therapy for the treatment of Barrett esophagus and esophageal adenocarcinoma. These investigations reinforce a sense of the complexity of GERD and provide optimism that modern technology will continue to be used to develop more effective treatments.

Journal Article↗

PubMed2000

A randomized, placebo-controlled, multicenter study of the safety and efficacy of a new polyethylene glycol laxative.

OBJECTIVE: This study was designed to determine the efficacy and safety of a new laxative, Braintree polyethylene glycol (PEG) laxative (Miralax, Braintree Laboratories, Braintree, MA). METHODS: This investigation was designed as a placebo-controlled, blinded, randomized, multicenter parallel trial. Study subjects were constipated but otherwise healthy outpatients who had < or =2 stools during a 7-day qualification period. Braintree PEG laxative 17 g or dextrose placebo p.o. in 8 oz of water for a 14-day treatment period. A diary recorded each bowel movement and subjective symptoms of stool consistency, ease of passage, cramps, and flatus. CBC, blood chemistries and urinalysis were performed before and after the treatment period. RESULTS: There were 151 randomized subjects, 131 female and 20 male. An increase in bowel movement frequency was observed with the PEG laxative as compared to placebo (p<0.001), with the greatest difference in efficacy in wk 2 of treatment (p<0.001). By wk 2 of treatment, on average, placebo subjects had 2.7 bowel movements/wk and PEG-treated study subjects had 4.5 movements/wk (p<0.01), or more than one bowel movement every 2 days. Investigator (p<0.005) and patient (p<0.001) subjective assessment of perception of treatment effectiveness, and patient evaluations of stool consistency and passage showed significant improvement in the active treatment group (p<0.001). There were no significant differences in laboratory changes or adverse experiences recorded between groups. CONCLUSION: Braintree PEG laxative is safe and effective in the short term for the treatment of constipation.

Adult↗

PubMed2000

Lumen-to-surface pH gradients in opossum and rabbit esophagi: role of submucosal glands.

The opossum esophagus, like that of humans, contains a network of submucosal glands with the capacity to secrete bicarbonate ions into the esophageal lumen. To evaluate the role of these glands in protecting the epithelial surface from acid insult, we measured the lumen-to-surface pH gradient in opossum esophagus at different luminal pH and compared it to that of rabbit esophagus, an organ devoid of submucosal glands. Sections of opossum and rabbit esophageal epithelium were mounted luminal side up in a modified Ussing chamber. pH-sensitive microelectrodes, positioned within 5 microm of the epithelial cell surface, were used to monitor surface pH during perfusion with solutions of different pH. At luminal pH 7. 5, the pH(s) of both opossum and rabbit were similar (pH(s) = 7.5). Lowering luminal pH from 7.5 to 3.5 in opossum decreased pH(s) to 4.2+/-0.16, a value significantly higher than pH of perfusate, whereas in rabbit this maneuver decreased pH(s) to 3.69+/-0.08, a value not significantly different from pH of perfusate. In opossum but not in rabbit, addition of carbachol to the serosal solution increased basal pH(s) to 7.8+/- 0.1 and significantly blunted the decline in pH(s) on perfusion with acidic Ringer solution (pH 3.5), with pH(s) falling to 5.6+/-0.45. The effect of carbachol on surface buffering was inhibited by prior treatment with atropine. Luminal acidification to pH 2.0 in opossum (as in rabbit) abolished the lumen-to-surface pH gradient even after addition of serosal carbachol. We conclude that the presence of submucosal glands in esophagus contributes through bicarbonate secretion to creation of a lumen-to-surface pH gradient. Although this gradient can be modulated by carbachol, its capacity to buffer (and therefore to protect) the epithelial surface against back-diffusing H(+) is limited and dissipated at pH 2.0.

Acids↗

PubMed1999

Esophageal exposure to ethanol increases risk of acid damage in rabbit esophagus.

Heavy alcohol consumption is associated with the development of reflux esophagitis. Among the reasons for this are impairment of the antireflux barrier, stimulation of acid secretion, and altered tissue resistance. To explore the contribution of altered tissue resistance to the development of esophagitis, sections of rabbit esophageal epithelium were mounted in Ussing chambers and exposed luminally to 10% ethanol, acid (HCl, pH 2), or combinations of both. Tissue injury was assessed by measurements of potential difference (PD), short circuit current (Isc) and electrical resistance (R) and by histology. Tissues exposed luminally to HCl for 1 hr exhibited little or no change electrically or morphologically compared to Ringer controls, while luminal exposure to 10% ethanol for 1 hr lowered PD (53 +/- 4%), Isc (30 +/- 1%), and R (31 +/- 5%) and produced cellular edema in the upper layers. Simultaneous exposure to ethanol and acid resulted in significantly greater declines in PD (81 +/- 1%) and Isc (70 +/- 2%), but not R (40 +/- 4%), and greater morphologic damage. Moreover, this vulnerability of ethanol-exposed tissues to acid was demonstrable at generally innocuous levels of acidity (pH 2-4), after only short periods of ethanol exposure (10 min) and with delays for acid exposures of up to 1 hr following ethanol removal from the bathing solution. In conclusion, ethanol has a direct noxious effect on esophageal epithelium, which predisposes the tissue to acid injury. Tissue vulnerability develops with even short exposures to clinically relevant concentrations of ethanol, lasts for at least 1 hr after ethanol clearance, and transforms relatively innocuous concentrations of acid into damaging agents. These results support the likelihood that ethanol's ability to alter tissue resistance plays an important role in the development of reflux esophagitis in humans.

Animals↗

PubMed1999

Is the esophageal squamous epithelial barrier function impaired in patients with gastroesophageal reflux disease?

BACKGROUND: A disturbed epithelial barrier function has been promoted as one factor in the pathogenesis of gastroesophageal reflux disease (GERD). We therefore studied the effect of acid perfusion on the transmural potential difference (PD) of the distal esophagus in relation to onset of reflux symptoms. METHODS: PD was assessed during perfusion with saline and with 0.1 M HCl in healthy controls (n = 17) and in GERD patients without (n = 15) or with esophagitis (n = 6) and in remission after a fundoplication (n = 10). Heartburn and other upper GI symptoms were recorded concomitantly. Endoscopy-negative patients were studied before and after omeprazole treatment. RESULTS: HCl perfusion induced more lumennegative peak PD values in patients with active GERD, regardless of the presence or absence of esophagitis, than in healthy controls. After successful therapy, the PD response to acid perfusion equalled that of healthy subjects. Acid perfusion was associated with the onset of heartburn in most patients with active GERD but in none of the healthy subjects, and less frequently after medical and surgical therapy. CONCLUSIONS: The epithelial permeability to hydrogen ions differs between healthy subjects and patients with active GERD. Effective treatment, such as omeprazole or fundoplication, might improve the barrier function.

Adolescent↗

PubMed1999

Esophageal submucosal glands: structure and function.

A three-tiered defense system exists in the esophagus, which serves a dual purpose of both limiting the degree of gastroesophageal reflux and minimizing the risk of acid-induced mucosal injury. The antireflux barrier, composed of both the lower esophageal sphincter and the diaphragmatic pinchcock, is the first line of defense and serves to limit the frequency and volume of refluxed gastric contents. When the antireflux barrier fails, the second line of defense, esophageal clearance, comes into play and serves to limit the duration of contact between gastric contents and the esophageal epithelium. Mechanisms involved in esophageal clearance include gravity and esophageal peristalsis, which remove volume, and secretions from swallowed saliva and esophageal submucosal glands, which neutralize acid. The third line of defense, tissue resistance, is necessary when acid contact time is prolonged such as when esophageal clearance is either ineffective or not operative (e.g., during sleep). Most studies that have examined esophageal clearance mechanisms have focused on the roles of esophageal peristalsis and salivary secretion, but the role of submucosal gland secretions is less well understood. This article reviews the structure and function of esophageal submucosal glands and discusses the potential role of their secretory products in esophageal clearance and tissue resistance.

Animals↗

PubMed1999

Mechanisms of basolateral Na+ transport in rabbit esophageal epithelial cells.

We examined the mechanisms of cellular Na+ transport, both Cl- dependent and Cl- independent, in the mammalian esophageal epithelium. Rabbit esophageal epithelium was dissected from its muscular layers and mounted in a modified Ussing chamber for impalement with ion-selective microelectrodes. In bicarbonate Ringer, transepithelial potential difference was -14.9 +/- 0.9 mV, the transepithelial resistance (RTE) was 1,879 +/- 142 Omega. cm2, the basolateral membrane potential difference (VmBL) was -53 +/- 1.5 mV, and the intracellular activity of Na+ (aNai) was 24.6 +/- 2.1 mM. Removal of Na+ and Cl- from the serosal and luminal baths decreased aNai to 6.6 +/- 0.6 mM. Readdition of Na+ to the serosal bath in the absence of Cl- increased aNai by 21.8 +/- 3.0 mM, whereas VmBL and RTE remained unchanged. When serosal Na+ was readded in the presence of amiloride the increase in aNai and the rate of Na+ entry were decreased by approximately 50%. 5-(N-ethyl-N-isopropyl)amiloride mimicked the effect of amiloride, whereas phenamil did not. Subsequent readdition of Cl- to the serosal bath further increased aNai by 4.4 +/- 1.9 mM. When the cells were acid loaded by pretreatment with NH+4 in nominally HCO-3-free Ringer, intracellular pH measurements showed a pHi recovery that is dependent on the presence of Na+ in the serosal bath and that can be blocked by amiloride. These data indicate that esophageal epithelial cells possess a Na+-dependent, amiloride-sensitive electroneutral mechanism for Na+ entry consistent with the presence of a basolateral Na+/H+ exchanger. The ability of Cl- to further enhance Na+ entry supports the existence of at least one additional Cl--dependent component of basolateral Na+ entry.

Amiloride↗

PubMed1999

Effect of heat stress on rabbit esophageal epithelium.

Hot beverages expose the esophageal epithelium to temperatures as high as 58 degrees C. To study the impact of such temperatures, rabbit esophageal epithelium was exposed to luminal heat or both luminal and serosal heat while mounted in Ussing chambers. Luminal heat, mimicking exposure to hot beverages, reduced potential difference (PD) and resistance (R) when applied at >/=49 degrees C and reduced short-circuit current (Isc) at >/=60 degrees C. At >/=60 degrees C, subepithelial blisters developed. Higher temperatures reduced R only moderately and reversibly. In contrast, the Isc declined sharply and irreversibly once threshold was reached. Luminal and serosal heat also reduced PD, Isc, and R, although the threshold for reduction in Isc was now similar to that for R. Additionally, luminal and serosal heat reduced Isc more than R for any given temperature and resulted in blisters at lower temperatures (50 degrees C) than luminal heat alone. The heat-induced decline in Isc was attributed in part to inactivation of Na-K-ATPase activity, although other transport systems could have been equally affected, and the decline in R to an increase in paracellular permeability. The latter effect on R also contributed to an increase in tissue sensitivity to luminal acid damage. Consumption of hot beverages exposes the esophagus to temperatures that can negatively impact epithelial structure and function. Impaired barrier function by heat increases the risk of esophageal damage by subsequent contact with (refluxed) gastric acid. These findings help explain in part the association between esophageal disease and consumption of hot beverages.

Animals↗