Biomedical subjects
M S Medow
Publications and source records attributed to M S Medow.
Esophageal dysmotility elicited by acid perfusion in children with esophagitis.
OBJECTIVE: To determine the importance of acid reflux-induced dysmotility in the genesis of noncardiac chest pain in children. METHOD: We performed esophageal manometries during intraesophageal perfusion with 0.9% NaCl or 0.1 N HCl in 19 children (age, 14.5 +/- 0.5 yr) with gastroesophageal reflux, biopsy-proven esophagitis, and complaints of at least one episode of chest pain per day. RESULTS: Baseline esophageal motilities were normal in all patients. Eight of 19 children (42%) complained of chest pain during intraesophageal acid perfusion. In three of these eight patients, complaints of chest pain during acid perfusion were temporally associated with "conversion" of previously normal motility patterns to manometric tracings, indicating esophageal dysmotility. Compared with findings during saline perfusion, esophageal acid exposure in these three children resulted in significant increases in both the duration (13.6 +/- 4.0 vs 3.2 +/- 0.2 s, p < 0.05) and amplitude (105.2 +/- 7.8 vs 61.2 +/- 2.1 mm Hg, p < 0.05) of esophageal contractions during wet swallows. Symptoms of chest pain resolved in all patients after therapy with H2-receptor antagonists. CONCLUSIONS: These data represent the first demonstration of acid-induced esophageal dysmotility in children with chest pain and suggest that reflux-induced motor abnormalities contribute to the onset and/or exacerbation of chest pain in pediatric patients with gastroesophageal reflux and esophagitis.
Ontogeny of proximal colon basolateral membrane lipid composition and fluidity in the rabbit.
Basolateral membranes from rabbit proximal colon were prepared from isolated colonocytes throughout postnatal maturation, using a modification of published techniques. In suckling (14-20 day) and post-weaning/mature (35-49 day) animals, membranes were purified approx. 10-fold, based upon the enrichment of ouabain-sensitive, sodium-potassium dependent adenosine triphosphatase activity. Membrane lipid analyses demonstrated age-dependent increases in total cholesterol and the cholesterol/phospholipid molar ratio, as well as decreases in phosphatidylethanolamine content and the fatty acid unsaturation index. Fluidity of basolateral membranes and membrane liposomes, determined from fluorescence anisotropy measurements using the lipid probes 1,6-diphenyl-1,3,5-hexatriene and DL-12-(9-anthroyl)stearic acid, demonstrated significant, ontogenic decreases in fluidity; and, additional studies showed that fluidity changes occurred early in the weaning period (by day 24 postnatally). Arrhenius plots of liposome anisotropies suggested a bilayer lipid thermotropic transition temperature of 22 degrees C in sucklings 26 degrees C in mature rabbits. These findings demonstrate that ontogeny of colonic basolateral membranes is associated with significant modulations in lipid composition and fluidity.
Spectrum of esophageal disorders in children with chest pain.
The charts of 83 children with chest pain who underwent esophageal manometry followed by esophagogastroscopy were reviewed. Forty-seven (57%) had normal esophageal histology and normal motility (group I). Esophagitis and normal motility were demonstrated in 15 children (group II), normal esophageal histology and esophageal dysmotility in 13 (group III), and both esophagitis and abnormal motility in 8 (group IV). Diffuse esophageal spasm and achalasia were the most common motility disorders identified (in seven and four patients, respectively). The presence and duration of symptoms, the age, and the gender were not different among the four patient groups. After six months of H2-receptor blockade, 12 of 15 group II patients were asymptomatic, whereas a significantly smaller percentage (five of 18) of patients with abnormal esophageal motility responded to esophageal dilation or treatment with calcium channel blockade, H2-receptor antagonist, and/or prokinetic agents (P less than 0.01). These data suggest that the evaluation of children with chest pain should include esophageal motility testing and esophagoscopy, even in the absence of other gastrointestinal-associated symptoms, and that while treatment of esophagitis results in resolution of symptoms, motility disorders were relatively refractory to therapy.
Glucocorticoid-mediated alterations in fluidity of rabbit cardiac muscle microvessel endothelial cell membranes: influences on eicosanoid release.
Experiments were conducted to determine effects of the synthetic glucocorticoid, dexamethasone, on the lipid fluidity of cultured rabbit cardiac muscle microvessel endothelial cells and the possible role(s) for altered fluidity in the steroid inhibition of cellular eicosanoid production. Following a sixteen hour exposure to 10(-7) M dexamethasone, membranes prepared from treated cells exhibited a decreased fluidity compared to their control counterparts, as assessed by steady-state fluorescence polarization techniques using 1,6-diphenyl-1,3,5-hexatriene (DPH). Examination of the effects of temperature on the anisotropy values of DPH using Arrhenius plots revealed consistent differences in the steroid treated cells over the entire temperature range (40-5 degrees C). These dexamethasone-dependent fluidity changes were associated with increases in the cholesterol/phospholipid ratio of membrane lipids. Restoration of membrane fluidity to control values with the fluidizing agent, 2-(2-methoxyethoxy)ethyl-8-(cis- 2-n-octylcyclopropyl)octanoate (A2C), partially reversed dexamethasone induced inhibition of A23187-stimulated eicosanoid release. These observations suggest that at least part of dexamethasone's inhibitory actions on eicosanoid generation in microvessel endothelial cells are mediated by alterations in membrane composition and fluidity.
Noncardiac chest pain in adolescents and children with mitral valve prolapse.
Chest pain in adolescents and children is usually not of cardiac origin. Of cardiac conditions commonly linked to chest pain in childhood, mitral valve prolapse (MVP) is the most prevalent, but this association has recently been questioned. In light of recent reports of gastroesophageal sources of chest pain in adults with MVP, we performed a comprehensive gastroesophageal evaluation of 17 preadolescents and adolescents with mitral valve prolapse who had chest pain as their presenting symptom. Evaluation consisted of esophageal manometry, Bernstein test, esophageal pH probe, and/or esophagogastroscopy. Fourteen of the 17 patients had at least one abnormal finding. Five patients had esophagitis, five had gastritis, one had high-amplitude esophageal contractions, one had abnormal esophageal manometry with positive Bernstein test, one had esophageal reflux and positive Bernstein test, and one had abnormal manometry with esophageal reflux. The 13 patients with esophagitis, gastritis, reflux, or positive Bernstein test were treated with antacid, with resolution of chest pain in 12 patients. Two of these patients underwent follow-up endoscopy with documentation of improvement. The patient with high-amplitude esophageal contractions was treated with dicyclomine, which resulted in resolution of chest pain. The observation that the chest pain was not related to mitral valve prolapse is important in clinical practice and raises further questions as to whether mitral valve prolapse causes chest pain.
Esophageal chest pain in children with asthma.
Sixteen patients with asthma and chest pain of greater than 2 months duration underwent gastroenterological evaluation utilizing fiber-optic esophagogastroduodenoscopy (EGD), esophageal manometry, and Bernstein testing. Eleven of 16 patients (75%) had endoscopic and histologic evidence of esophagitis. One patient with esophagitis exhibited high-amplitude peristaltic contractions during motility testing. Four of these 11 patients (36%) had a positive Bernstein test. Extended intraesophageal pH monitoring of seven patients with esophagitis revealed significant gastroesophageal reflux (GER) in all of these patients. Chest pain was associated with an episode of GER in three patients (43%). Nine of 11 patients (82%) with esophagitis responded to medical therapy, resulting in resolution of esophageal inflammation and chest pain. One patient required Nissen fundoplication surgery after failure of medical therapy, and one patient who refused surgery progressively developed more severe esophagitis during 9 months of medical therapy. Children with asthma may have chest pain due to gastroesophageal reflux-associated esophagitis that usually responds to medical therapy.
Effect of low-density lipoprotein on endothelial cell membrane fluidity and mononuclear cell attachment.
To determine the effects of prolonged low-density lipoprotein (LDL) exposure in vitro on cultured endothelial cell (EC) lipid dynamics and cellular function, human umbilical vein ECs were incubated in LDL concentrations [cholesterol (Chol) = 240 mg/dl] associated with the premature development of atherosclerosis. After 4 days of incubation, cells were examined for changes in cellular lipid composition and for membrane fluidity. Results indicate that LDL-EC have increased Chol content (control EC vs. LDL-EC = 22.4 +/- 5.26 vs. 38.9 +/- 0.24 nmol/10(6) cells, P less than 0.05) and cellular Chol-to-phospholipid ratio (0.61 +/- 0.10 vs. 1.21 +/- 0.10 mol/mol, P less than 0.05). Augmentation of EC Chol content was accompanied by a marked decrease in EC cellular membrane fluidity as assessed by fluorescence polarization (anisotropy, r values, 0.172 +/- 0.019 vs. 0.226 +/- 0.014, P less than 0.0001). LDL-induced changes in EC lipid dynamics were associated with enhanced EC binding of monocytes (P less than 0.05) and U937 cells (P less than 0.01). Both LDL-induced decreases in membrane fluidity and enhanced attachment of mononuclear cells were reversed to control levels following a 2-min incubation of LDL-EC with the membrane mobility agent, A2C. These data therefore suggest that LDL-induced modulations in lipid dynamics play an important role in perturbation of EC function.
Excess membrane cholesterol alters calcium movements, cytosolic calcium levels, and membrane fluidity in arterial smooth muscle cells.
The relations between membrane cholesterol content, basal (unstimulated) transmembrane 45Ca2+ movements, cytosolic calcium levels, and membrane fluidity were investigated in cultured rabbit aortic smooth muscle cells (SMCs) and isolated SMC plasma membrane microsomes. SMCs were enriched with unesterified (free) cholesterol (FC) for 18-24 hours with medium containing human low density lipoprotein and FC-rich phospholipid (PL) liposomes. This procedure increased cholesterol mass without affecting PL mass, resulting in an increase in the FC/PL molar ratio compared with controls in cells (67% FC increase, p less than 0.001; 43% FC/PL ratio increase, p less than 0.01) and in SMC microsomes (52% FC increase, p less than 0.05; 43% FC/PL ratio increase, p less than 0.05). Cholesterol enrichment also increased unstimulated 45Ca2+ influx (p less than 0.001) and efflux (p less than 0.05). Cellular cholesterol content correlated in a linear fashion with these changes (influx: r = 0.722, p less than 0.01; efflux: r = 0.951, p less than 0.05). In addition, cytosolic calcium levels increased approximately 34% (p less than 0.01) with cholesterol enrichment. The cholesterol-induced increase in 45Ca2+ influx was reversible with time and demonstrated sensitivity to the channel blockers. Fluorescence anisotropy measured from 5 degrees C to 40 degrees C using the fluorophore diphenylhexatriene showed decreased membrane fluidity in microsomal membranes obtained from cholesterol-enriched SMCs compared with controls (p less than 0.02). These results suggest that the SMC plasma membrane is very sensitive to cholesterol enrichment with liposomes or human low density lipoprotein and that increases in membrane cholesterol content increase cytosolic calcium levels in SMCs, are associated with a decrease in membrane fluidity, and unmask a new, or otherwise silent, dihydropyridine-sensitive calcium channel that may be involved in altered arterial wall properties with serum hypercholesterolemia.
Unfolding transitions of fibronectin and its domains. Stabilization and structural alteration of the N-terminal domain by heparin.
Changes in the conformational state of human plasma fibronectin and several of its fragments were studied by fluorescence emission, intrinsic fluorescence polarization and c.d. spectroscopy under conditions of guanidinium chloride-and temperature-induced unfolding. Fragments were chosen to represent all three types of internal structural homology in the protein. Low concentration (less than 2 M) of guanidinium chloride induced a gradual transition in the intact protein that was not characteristic of any of the isolated domains, suggesting the presence of interdomain interactions within the protein. Intermediate concentrations of guanidinium chloride (2-3 M) and moderately elevated temperatures (55-60 degrees C) induced a highly co-operative structural transition in intact fibronectin that was attributable to the central 110 kDa cell-binding domain. High temperatures (greater than 60 degrees C) produced a gradual unfolding in the intact protein attributable to the 29 kDa N-terminal heparin-binding and 40 kDa collagen-binding domains. Binding of heparin to intact fibronectin and to its N-terminal fragment stabilized the proteins against thermal unfolding. This was reflected in increased delta H for the unfolding transitions of the heparin-bound N-terminal fragment, as well as decreased accessibility to solvent perturbants of internal chromophores in this fragment when bound to heparin. These results help to account for the biological efficacy of the interaction between the fibronectin N-terminal domain and heparin, despite its relatively low affinity.
Beta-galactosidase tablets in the treatment of lactose intolerance in pediatrics.
Lactose-intolerant children manifest diminished or nonexistent intestinal lactase activity, resulting in flatulence, abdominal pain, and diarrhea. To assess the hydrolytic capability of lactase-containing tablets taken immediately before oral lactose challenge, we studied 18 children previously identified as being lactose intolerant and having no underlying organic gastrointestinal disease. Subjects had a mean (+/- SEM) age of 11.4 +/- 3.4 years; 72% were male. At time of the study, lactase-containing tablets or placebo tablets were ingested (double-blind) immediately before drinking a solution of lactose. Breath samples were obtained for hydrogen analysis at 30-minute intervals during a 2-hour period, and clinical symptoms were monitored. In lactose-intolerant patients, hydrogen production was significantly greater following placebo (maximum hydrogen excretion, approximately 60 ppm) compared with lactase-containing tablets (maximum hydrogen excretion, 7 ppm). Increased hydrogen production was associated with clinical symptoms including abdominal pain (89% of subjects following placebo ingestion), bloating (83%), diarrhea (61%), and flatulence (44%). These results indicate, therefore, that coingestion of lactose and lactase-containing tablets significantly reduces both breath hydrogen excretion and clinical symptoms associated with lactose intolerance.
Renal Fanconi syndrome: developmental basis for a new animal model with relevance to human disease.
Using succinylacetone (SA), a metabolite of tyrosine excreted in excess by infants and children with hereditary tyrosinemia and the renal Fanconi syndrome (FS), we have investigated developmentally-related membrane transport events leading to emergence of the generalized renal tubular dysfunction seen in human FS. SA was found to impair sugar and amino acid uptake by both newborn renal tubules and 7-day renal brush-border membrane vesicles (BBMV). This impairment by SA was due in part to a slowing of substrate cotransport rate of 22Na+-entry into BBMV. Concentration-dependent uptake studies indicated SA inhibited the newborn high-affinity transport systems for sugars and amino acids. SA also caused an increase in membrane fluidity and a shift in the thermotropic transition temperature. The demonstrated dual nature of SA's effect on membrane fluidity and O2 consumption, together with the relative contribution of each component to SA-induced transport impairment helps to provide a basis for an understanding of the age-related increases in glucosuria, aminoaciduria and natriuria seen in infants with FS.
Campylobacter pylori-related gastrointestinal disease in children. Incidence and clinical findings.
Over a one-year period, 95 children and adolescents presenting with epigastric pain and/or vomiting, and without associated risk factors for development of peptide disease, underwent endoscopic antral biopsies for pathologic diagnosis and to detect presence of Campylobacter ss. pylori (C. pylori). Additional biopsies of the esophagus, stomach, and duodenum were obtained for histologic evaluation. C. pylori was identified in 16 patients (16.8%), all of whom had evidence of acute and/or chronic gastritis. Significant discriminating factors between C. pylori-positive and -negative subjects included age at presentation (positive vs negative = 14.6 vs 9.9 years, P less than 0.01), biopsy-confirmed gastritis (100% vs 30.4%, P less than 0.001), and diagnosis of duodenitis alone (0% vs 46.8%, P less than 0.001). Risk for bacterial colonization was significantly higher in the presence of endoscopic gastritis (P less than 0.001). Among C. pylori-positive patients, none responded to standard antiulcer therapy (H2-receptor antagonists, antacids). Symptomatic and histologic remission was achieved utilizing combined therapy with bismuth subsalicylate and antibiotics. Seven of 79 C. pylori-negative patients with biopsy-proven gastritis who responded poorly to antisecretory therapy had the organism identified in follow-up antral biopsies; these patients improved clinically following treatment for C. pylori. These data suggest that C. pylori is a significant factor in the etiology of upper gastrointestinal tract inflammatory disease in pediatrics, and presence of the organism should be evaluated, particularly in children with evidence of acute and/or chronic gastritis.
Use of the intraesophageal acid perfusion test in provoking nonspecific chest pain in children.
The intraesophageal acid perfusion (Bernstein) test was evaluated as a provocative test for nonspecific chest pain in children with esophagitis. Sixty patients with atypical chest pain were studied. None of the patients had heartburn or other characteristic symptoms of esophagitis. Forty-five patients had esophagitis; in 18 (40%) of these patients, pain replicating their usual symptoms developed during esophageal acid perfusion, whereas in 15 patients without esophagitis, chest pain did not develop during esophageal acid perfusion. In three patients with esophagitis, esophageal manometric abnormalities and chest pain developed as a result of esophageal acid perfusion. Treatment with either ranitidine or antacids had equivalent effectiveness. We conclude that a positive Bernstein test result in children with nonspecific chest pain indicates that the pain is likely associated with esophageal disease.
Patterns of gastroesophageal reflux (GER) in patients with apparent life-threatening events.
The incidence and temporal patterns of gastroesophageal reflux (GER) in infants presenting with an apparent life-threatening event (ALTE) was compared with GER characteristics of infants evaluated for persistent emesis, utilizing continuous 24 h intraesophageal pH monitoring. These data indicate that the incidence of significant GER was similar in both groups, despite the absence of a clinical vomiting history in 46% of ALTE patients. Furthermore, infants with ALTE demonstrate a significantly higher incidence of sleep reflux when compared with control infants presenting with vomiting alone (27 vs. 0%, p less than 0.001). Awake GER beyond the first two postprandial hours was not observed in either study group. Monitoring results, therefore, indicate that significant GER is common in infants with ALTE; and these infants manifest an apparently unique pattern of GER distinct from that observed in age-matched controls with GER alone. Possible relationships between GER in ALTE patients and the development/onset of apneic episodes are discussed.
Agonist-specific role for Na+-H+ antiport in prostaglandin release from microvessel endothelium.
Rabbit coronary microvascular endothelial (RCME) cells synthesize prostaglandin (PG) I2 and PGE2 in response to stimulation with human thrombin, ATP, and the Ca2+ ionophore, A23187. Replacement of extracellular Na+ with choline or N-methylglucamine reduced thrombin-stimulated PG secretion but did not significantly affect either ATP- or A23187-stimulated PG secretion. Pretreatment of RCME cells with Na+ channel or Na+ -Ca2+ exchange blockers did not alter PG release in response to any of these three agonists. Pretreatment of RCME cells with the specific Na+ -H+ antiport blockers 5-(N-ethyl-N-isopropyl)-amiloride (EIPA, 10 microM) and 5-(N,N-hexamethylene)-amiloride (HMA, 0.1 microM) significantly reduced thrombin but not A23187- or ATP-stimulated PG secretion. Studies with the intracellular pH indicator dye 2,7-bis(carboxyethyl)-5(6)-carboxyfluorescein demonstrated thrombin activation of Na+ -H+ antiport, an effect blocked by either HMA or EIPA. Since manipulations known to inhibit Na+ -H+ exchange (EIPA, HMA, replacement of Na+ with choline or N-methylglucamine) reduced thrombin-stimulated RCME cell PG release, we conclude that activation of Na+ -H+ exchange is involved in the coupling of thrombin interaction with RCME cells to subsequent phospholipase activation and PG release.
Dexamethasone effects on microvascular endothelial cell lipid composition.
Previous studies have shown that treatment of cultured rabbit coronary microvessel endothelial (RCME) cells with dexamethasone results in a dose-, time-, and glucocorticoid-dependent inhibition of prostaglandin release. In the present study, the effects of dexamethasone on RCME membrane lipid composition and release of arachidonic acid were examined. This study demonstrated that dexamethasone treatment did not significantly alter the relative distribution of membrane phospholipids but did result in changes of fatty acid composition. There was an increase in saturated and monounsaturated fatty acids and a decrease in polyunsaturated fatty acids. Dexamethasone treatment did not reduce A23187-stimulated arachidonic acid release, despite inhibiting prostaglandin release by 50%. Studies with radiolabeled arachidonic acid suggest that dexamethasone may exert some actions on membrane remodeling, an effect that will require further investigation. Our data strongly suggest that the inhibitory actions of glucocorticoids on prostaglandin release in cultured RCME cells are not the result of a generalized inhibition of arachidonic acid release, and alternate mechanisms must therefore be considered.
Ontogeny of basolateral membrane lipid composition and fluidity in small intestine.
To evaluate physicochemical properties of the small intestinal basolateral cell surface during postnatal development, membranes were isolated from suckling (14-17 days) and weanling-mature (35-49 days) rabbit jejunal and ileal enterocytes at 30- to 40-fold purification (based on Na+-K+-ATPase specific activity) and with limited contamination from coisolated cellular elements. Membrane lipid analysis demonstrated age-dependent reductions and proximal to distal increases in total lipid (per milligram protein). Postnatal increases in membrane total cholesterol of jejunum (suckling vs. mature, 0.18 vs. 0.26 mumol/mg protein; P less than 0.01) and ileum (0.18 vs. 0.31 mumol/mg protein; P less than 0.01) resulted in markedly higher cholesterol-to-phospholipid molar ratios (jejunum, 0.43 vs. 0.73; ileum, 0.43 vs. 0.72 mumol/mg protein; P less than 0.01). Membranes from mature animals had higher relative sphingomeylin and phosphatidylcholine content and, in both age groups, fatty acyl saturation was increased in ileum compared with jejunum. By utilization of the fluorophores 1,6-diphenyl-1,3,5-hexatriene and DL-12-(9-anthroyl)stearic acid, the fluidity of basolateral membranes and liposomes prepared from extracted membrane lipid decreased markedly in mature rabbits. Arrhenius plots demonstrated higher apparent thermotropic transition temperatures of mature membrane lipid. These data therefore demonstrate significant changes in small intestinal basolateral membrane lipid composition and fluidity that occur during the weaning period. Possible relationships to ontogenesis of membrane protein function are discussed.