Dimerization leads to changes in APP (amyloid precursor protein) trafficking mediated by LRP1 and SorLA.

Proteolytic cleavage of the amyloid precursor protein (APP) by α-, ß- and γ-secretases is a determining factor in Alzheimer's disease (AD). Imbalances in the activity of all three enzymes can result in alterations towards pathogenic Aß production. Proteolysis of APP is strongly linked to its subcellular localization as the secretases involved are distributed in different cellular compartments. APP has been shown to dimerize in cis-orientation, affecting Aß production. This might be explained by different substrate properties defined by the APP oligomerization state or alternatively by altered APP monomer/dimer localization. We investigated the latter hypothesis using two different APP dimerization systems in HeLa cells. Dimerization caused a decreased localization of APP to the Golgi and at the plasma membrane, whereas the levels in the ER and in endosomes were increased. Furthermore, we observed via live cell imaging and biochemical analyses that APP dimerization affects its interaction with LRP1 and SorLA, suggesting that APP dimerization modulates its interplay with sorting molecules and in turn its localization and processing. Thus, pharmacological approaches targeting APP oligomerization properties might open novel strategies for treatment of AD.

Is vertebral body stenting in combination with CaP cement superior to kyphoplasty?

PURPOSE: In the evolution of the minimally invasive treatment of vertebral compression fractures, vertebral body stenting (VBS) was developed to reduce intraoperative and secondary loss of vertebral height. Particularly in combination with the usage of biodegradable cement, the influence of VBS on the rate of intraoperative complications and long-term outcome is unclear. The purpose of this study was to investigate the differences between balloon kyphoplasty (BKP) and VBS regarding their long-term clinical and radiological outcome in combination with calcium phosphate (CaP) application instead of polymethyl methacrylate (PMMA). METHODS: This retrospective study included 49 patients with fresh mono-segmental thoracolumbar fractures without neurological signs treated with VBS or BKP and CaP cement (Calcibone). The outcome was evaluated with the visual analogue pain scale (VAS), the Oswestry disability score (ODI), and radiologically assessed. RESULTS: In the course of the radiological follow-up, the VBS group showed statistically significant less vertebral height loss than the BKP group. However, with respect to VAS and ODI scores there were no statistically significant differences between the VBS and BKP group in the clinical follow-up. The rate of cement leakage was comparable in both groups. CONCLUSIONS: Both techniques facilitated good clinical results in combination with absorbable cement augmentation. In particular, the VBS enabled us to benefit from the advantages of the resorbable isothermic CaP cement with an improved radiological outcome in the long term compared to BKP. However, there was a mentionable loss of reduction in the follow-up in both groups compared to previously published data with PMMA cement. These slides can be retrieved under Electronic Supplementary Material.

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.

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.

Effects of ethinyl estradiol on intestinal membrane structure and function in the rabbit.

Structural and functional properties of the small intestinal microvillus membrane were evaluated in the rabbit after administration of ethinyl estradiol, a synthetic estrogen with a demonstrated propensity to alter hepatic membrane lipid fluidity, and promote cholestasis. In the jejunum, no estrogen-induced changes in microvillus membrane total lipid, cholesterol or phospholipid content were observed. However, the ileal microvillus membrane in estradiol-treated animals demonstrates significant reductions vs. controls (per mg protein) in total lipid (0.55 milligrams vs. 0.89 milligrams) [corrected] and phospholipid (206.7 micrograms vs. 304.91 micrograms) (p less than 0.001) content, as well as modifications in specific phospholipid species. The increase in the ileal microvillus membrane cholesterol: phospholipid molar ratio (0.65 vs. 0.51, p less than 0.05) was associated with a significant decrease in membrane lipid fluidity reflected by an increase in fluorescence anisotropy measurements utilizing diphenyl hexatriene as the fluorophore (r at 25 degrees C = 0.306 vs. 0.282, p less than 0.05). Thermotropic lipid phase transitions, assessed by Arrhenius plots of both fluorescence data and ileal microvillus membrane p-nitrophenylphosphatase activity demonstrate that phase changes occur between and 24 and 28 degrees C in both treated and untreated groups. Within the temperature range studied (40-10 degrees C) no differences from control were observed in microvillus membrane alkaline phosphatase activity following estrogen treatment. These data therefore indicate that ethinyl estradiol-induced effects on microvillus membrane lipid composition and physical properties occur predominantly in the ileum and appear to be related, in part, to specific alterations in the availability of phospholipid following estrogen treatment.

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.

A role for intermediate filaments in the establishment of the primitive epithelia during mammalian embryogenesis.

Investigations of the cytoskeleton in mammalian eggs and embryos have revealed the existence of an unusual array of crosslinked intermediate filaments composed of cytokeratins 5, 6, 16, and 'Z' that are referred to as cytoskeletal sheets. We have been investigating the function of these cytoskeletal sheets during embryogenesis. In this investigation we report the rapid appearance of extensive arrays of tonofilaments extending across blastomeres and in association with intercellular desmosomal junctions appearing at the time the embryo hatches from its zona pellucida, through the time of implantation of the embryo into the uterine wall. Just prior to the time of gastrulation these tonofilaments disappear. Electron microscopy and immunoconfocal microscopy demonstrate that the tonofilaments are composed of cytokeratins characteristic of the type found earlier in development, that is types 5 and 6; whereas, cytokeratin type 8 which has been shown to be synthesized in blastocysts is localized primarily at perinuclear regions. Cytokeratins 8 and 18 are synthesized to about the same extent as actin at the time the tonofilaments appear whereas the synthesis of cytokeratins 5 and 6 is greatly reduced. Our results suggest that cytokeratins 5 and 6 in the tonofilaments may arise from the stored form of cytokeratins in the cytoskeletal sheets. Consequently, our results suggest that the sheets may serve as a maternal reserve of cytokeratin employed by the embryo at the time of implantation to form extensive arrays of tonofilaments in the embryo that likely provide structural integrity to the embryo as it is subjected to mechanical stress during invasion and implantation into the uterine wall.

Effects of feeding on the small intestinal mucosa of beagle pups during the first 5 d of life.

To further define the effects of feeding on small intestinal ontogeny, naturally suckled and formula-fed beagle pups were studied over the first 120 h of life. In suckled animals, proximal jejunal and midintestinal mucosal weight and protein and DNA contents increased > 75% by 24 h (P < 0.005), with no further increases at 120 h. In formula-fed pups, no mucosal mass changes were found between 0 and 72 h of life. At 120 h, proximal jejunal mucosal weight and protein and DNA contents were significantly greater than in newborns (P < 0.005) and were similar to values for suckled animals at the same time. No significant mid-intestinal or terminal ileal growth was noted in formula-fed pups at any time. Specific and total activities of proximal jejunal brush border lactase, sucrase, and alkaline phosphatase were significantly greater in suckled vs formula-fed animals at 120 h. In a parallel study to assess postnatal effects of mature milk vs colostrum, significant mucosal growth at 24 h of life was demonstrated in pups suckled by surrogate dams who had whelped 21 d previously. These data indicate that both natural suckling (colostrum or milk) and formula feeding support enteric mucosal growth in newborn dogs; however, the two feeding regimens are characterized by unique ontogenic patterns of intestinal mucosal growth and function.

Gastroesophageal reflux associated with nemaline myopathy of infancy.

A severe infantile form of nemaline myopathy has a high mortality rate when untreated because of subsequent malnutrition and respiratory failure. Three infants with this condition demonstrated persistent vomiting, poor weight gain, and recurrent pneumonias. Esophageal manometry demonstrated decreased lower esophageal sphincter pressures and low amplitude peristalsis; 24-hour esophageal pH monitoring revealed significant gastroesophageal reflux. Medical therapy was ineffective in relieving symptoms. After antireflux surgery, vomiting and respiratory symptoms ceased, and there was no longer significant gastroesophageal reflux during pH monitoring. Our experience indicates that in some infants with nemaline myopathy a severe form of gastroesophageal reflux develops that is not responsive to medical therapy. Early surgical intervention may decrease life-threatening complications associated with gastroesophageal reflux in these infants.

Enteral nutrition in infants with congenital heart disease and growth failure.

To determine an effective nutritional regimen for management of growth failure in infants with congenital heart disease and congestive heart failure, the authors studied 19 infants with cardiac anomalies who were not candidates for early corrective surgery. Patients were randomly assigned to one of three feeding groups: group 1 (n = 7) received continuous, 24-hour nasogastric alimentation; group 2 (n = 5) received overnight, 12-hour nasogastric infusions plus daytime oral feedings as tolerated; and group 3 (n = 7) received oral feedings alone. For all patients, commercial infant formula (cow's milk or soy protein) was supplemented to a calorie density of approximately 1 kcal/mL. During a 5.25 +/- 0.45 month study period, only group 1 infants achieved intakes greater than 140 kcal/kg per day (mean = 147 kcal). Serial anthropometric measurements demonstrated that only 24-hour infusions (group 1) were associated with significantly improved nutritional status, when assessed by z scores for weight (P less than .01) and length (P less than .05). Group 1 infants also showed marked increases in midarm muscle circumference and triceps and subscapular skinfold thicknesses (P less than .01, compared with groups 2 and 3). These data suggest that infants with congenital cardiac defects complicated by malnutrition manifest increased nutrient requirements for growth and weight gain. Continuous, 24-hour, nasogastric alimentation is a safe and effective method for achieving both increased nutrient intake and improved overall nutritional status in these infants.

Lipid fluidity modulates platelet aggregation and agglutination in vitro.

To determine the effect of altered membrane fluidity on platelet aggregation/agglutination, fresh, washed human platelets were treated with A2C, a cyclopropyl fatty acid ester which is known to enhance mobility of intrinsic membrane bilayer constituents and increase membrane fluidity. Fluorescence polarization studies demonstrated A2C incubation time- and concentration-dependent increases in platelet membrane fluidity (decreased fluorescence anisotropy). Preincubation with A2C was associated with diminished collagen, thrombin and ristocetin-induced platelet aggregation/agglutination. Aggregation/agglutination was diminished by 93 +/- 5% for collagen (0.2 mg/ml), 53 +/- 3% for thrombin (1.0 U/ml) and 85 +/- 9% for ristocetin (1.1 mg/ml). These data suggest that membrane fluidity is involved in the regulation of platelet function.

Low blood selenium levels in patients with cystic fibrosis compared to controls and healthy adults.

Frank clinical selenium deficiency has been described in cystic fibrosis (CF), and a relative deficiency has been proposed as contributing to the pathogenesis of the disease. Because of these possibilities, we investigated the relationship between overall nutritional status in CF with measures of selenium nutriture. Fifteen stable outpatients with CF (group I) were compared to 13 age-matched controls (group II) and 27 healthy adults (group III). Whole blood, plasma, and red blood cell selenium levels were reduced by 31%, 29%, and 33%, respectively, in CF patients vs controls (all p less than 0.001). In addition, both groups I and II showed significantly lower blood selenium levels than healthy adults (p less than 0.005). Nutritional assessment revealed CF patients to be undernourished, with significant decreases in serum albumin (p less than 0.025), weight-for-height deficit (p less than 0.01), and weight-for-age (p less than 0.025) vs controls. However, only the triceps skinfold (TSF) measurement correlated significantly with selenium status (r = 0.56: p less than 0.05 for whole blood selenium vs TSF). We conclude, based on the magnitude of decrement in blood selenium, that it is unlikely that selenium plays a significant primary pathogenic role in cystic fibrosis. However, these patients are at high risk for developing clinical selenium deficiencies. The measurement of blood selenium levels using appropriate age-matched normal standards should be mandatory in all CF patients with malnutrition, or in those requiring parenteral nutritional support.

Cholesterol screening in children: should obesity be a risk factor?

To determine whether obesity should be added to the current American Academy of Pediatrics (AAP) criteria for cholesterol screening in childhood, the charts of 99 children referred for evaluation of either hypercholesterolemia (n = 53) or obesity (n = 45) were reviewed. Compared with obese children, nonobese hypercholesterolemic subjects were younger (8.4 vs 11.4 years) and had lower mean body mass index and % ideal body weight. Frequency of elevated (> 90th percentile for age) total and low-density lipoprotein cholesterols were similar in both groups. Fifty-three of 65 children who met the current AAP criteria were hypercholesterolemic, however, 23/76 hypercholesterolemic children failed to satisfy these screening criteria. Thirty-six of 45 obese children had cholesterol levels > 90th percentile, suggesting increased risk for hypercholesterolemia in this group. If obesity was added to the AAP criteria, 66/80 hypercholesterolemic subjects would have been identified. These modified criteria, vs AAP standards, significantly improved both their sensitivity (70 vs 87%, p < 0.02) and negative predictive value (45 vs 30%, p < 0.02). Pending further studies in larger pediatric populations, these data indicate that obesity should be considered a risk factor for hypercholesterolemia in childhood, and we recommend modifying the AAP screening criteria to include obese children.

Estrogen modulates ileal basolateral membrane lipid dynamics and Na+-K+-ATPase activity.

The effects of ethinyl estradiol, a synthetic estrogen with cholestatic properties and a propensity to alter hepatocyte and ileal brush-border membrane fluidity, on lipid structure and Na+-K+-ATPase activity of rabbit small intestinal basolateral membranes were determined. Utilizing the fluorophores 1,6-diphenyl-1,3,5-hexatriene and DL-12-(9-anthroyl)stearic acid, increases in fluorescence anisotropy, the reciprocal of fluidity, were found in basolateral membranes and in membrane lipid liposomes isolated from ileum. Fluidity alterations were accompanied by a marked decrease in bilayer phospholipids (0.37 vs. 0.48 mumol/mg protein; P less than 0.01) and an increase in both the cholesterol-to-phospholipid molar ratio (0.85 vs 0.61; P less than 0.02) and membrane saturated fatty acid content. Estrogen-mediated physicochemical changes were associated with a significant reduction in ileal basolateral membrane Na+-K+-ATPase specific activity (100.0 vs. 185.8 nmol Pi.min-1.mg protein-1; P less than 0.02). Control values both for fluorescence anisotropy and for Na+-K+-ATPase specific activity were restored after in vitro membrane fluidization with benzyl alcohol. The data therefore indicate that ethinyl estradiol effects on basolateral membrane lipid dynamics are confined to the ileum and are associated with inhibition of Na+-K+-ATPase activity. These structural and functional changes appear to be related, in part, to specific modifications in the availability of phospholipid after estrogen treatment.

Taurocholate transport by brush-border membrane vesicles from the developing rabbit ileum: structure/function relationships.

To examine the ontogenesis of bile acid transport in the rabbit ileum, brush-border membrane vesicles (12- to 20-fold purified) were prepared from 14- to 49-day-old animals. Taurocholate uptake was characterized by the emergence of secondary active, Na(+)-dependent transport at the start of weaning (21 days). Transient intravesicular accumulation (overshoot) of taurocholate occurred at 5-10 s of incubation, and the overshoot maximum increased significantly from 21 days (349.2 +/- 22.4 nmol/mg protein) to 35 days (569.0 +/- 84.3 nmol/mg protein; p less than 0.001), without further increase at maturity (49 days, not equal to 607.6 +/- 136.7 nmol/mg protein). No significant taurocholate active uptake component was noted at 14 days; however, ileal vesicles from sucklings showed carrier-mediated, Na+ D-glucose cotransport. In greater than or equal to 35-day-old rabbits, osmolarity studies at 20 s of incubation showed that only approximately 12% of [14C]taurocholate uptake was secondary to bile acid-to-membrane binding. Conversely, at 20 min, greater than 95% of radiolabel incorporation represented solute bound to the external and/or internal membrane surface. Arrhenius plots establish brush-border membrane taurocholate uptake as an intrinsic, lipid-dependent process, with a slope discontinuity between 24 and 28 degrees C, similar to the membrane lipid thermotropic transition region. Steady-state fluorescence polarization studies (1,6-diphenyl-1,3,5-hexatriene) demonstrate a temporal association between the maturation of taurocholate uptake and age-related decreases in ileal brush-border membrane fluidity. These data indicate that maturation of bile acid secondary active transport in the rabbit ileum may be regulated, at least in part, by changes in brush-border membrane lipid dynamics.

Colostrum-induced enteric mucosal growth in beagle puppies.

To evaluate the role of artificial feeding and natural feeding in early growth of enteric mucosa, we determined enteric mucosal mass, protein and DNA content, and disaccharidase activities in beagle puppies at birth, and after 24 h of either natural or artificial feeding. Despite similar increases in body weight over the first 24 h of life, neither mucosal mass, DNA content, nor protein content of the artificially fed animals was different from that of newborn animals. In contrast, mucosal mass of the suckled animals was 75% greater, DNA content was 56% greater, and protein content was 93% greater than that of newborn animals. The mucosal protein/DNA ratio of the suckled animals was greater than that of newborn, but not artificially fed animals. The greater DNA, protein, and protein/DNA ratio in this group suggest that the greater mucosal mass is a result of both cellular hyperplasia and hypertrophy. Sucrase specific activity of the suckled animals was less than that of the artificially fed but not the newborn animals. Other disaccharidase activities were not different among the three groups. These data extend the findings of Widdowson et al.(25) to another species and demonstrate that this rapid enteric growth over the first day of life results only from natural feeding. They strongly suggest, therefore, that rapid early enteric growth, mediated perhaps by a factor in natural milk that stimulates enteric mucosal growth, is an important heretofore unappreciated phase of intestinal development.

Protein kinase C, a pivotal regulator of hamster egg activation, functions after elevation of intracellular free calcium.

We investigated the signal transduction pathways that mediate activation of Syrian hamster eggs. Under conditions in which the concentration of intracellular free calcium ([Ca2+]i) is clamped low, activation of protein kinase C (PKC) can induce second polar body formation, reformation of the nuclear envelope, and decondensation of chromatin, as well as golgi reformation. However, calcium is necessary for normal transition from meiotic metaphase II to anaphase II. Conversely, under conditions in which the level of PKC activity is clamped low, induction of a rise in [Ca2+]i, using the calcium ionophore A23187, does not induce egg activation. These results strongly suggest that PKC acts after the calcium signal as a proximal inducer of egg activation. This suggestion is supported by the kinetics of egg activation; PKC stimulators activate the eggs at a significantly enhanced rate (P < 0.01) compared with activation by calcium ionophore. We show here that PKC stimulators induce emission of the second polar body, but that subsequently, with longer culture, the emitted polar body is absorbed. Our results suggest that the rise in [Ca2+]i serves two functions, to activate PKC and to induce the transition from metaphase II to anaphase II. PKC, once activated, mediates several other events of egg activation.

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.

Esophagitis and Helicobacter pylori in children: incidence and therapeutic implications.

The relationship between gastric Helicobacter pylori colonization and esophagitis was determined in 457 children undergoing endoscopic evaluation of abdominal pain and/or vomiting. In all patients, biopsies of the esophagus were examined histologically, and two antral biopsies were analyzed for the presence of H. pylori, using standard microbiological and histochemical techniques. The incidence of biopsy-proven esophagitis was similar in H. pylori-positive (15/56 patients) and -negative (94/401; p = NS) groups. Clinical improvement, after 2 months of antisecretory therapy with H2-receptor antagonists, was independent of H. pylori status (11/15 vs. 68/94 responders; p = NS). All 26 H. pylori-negative nonresponders became asymptomatic with a second course of H2-blockers. The 4/15 H. pylori-positive patients (all of whom had associated gastritis/duodenitis) who failed antisecretory therapy responded clinically to treatment with amoxicillin plus bismuth subsalicylate. These data indicate that primary treatment of biopsy-confirmed esophagitis in children should include anti-secretory agents, regardless of H. pylori status. A small percentage of H. pylori-positive patients with esophagitis and concomitant gastroduodenal inflammation may require additional antibacterial therapy, suggesting that presence of the organism should be assessed in all pediatric patients undergoing upper endoscopic evaluation.

Respiratory methane excretion in children with lactose intolerance.

To evaluate the relationship between colonic methane production and carbohydrate malabsorption, we measured end-expiratory methane levels in 70 normal and 40 lactose-intolerant children. Time-dependent excretion of hydrogen and methane was determined every 30 min for 120 min following a fasting oral lactose challenge (2 g/kg). Mean breath hydrogen levels in normals (lactose-tolerant) equaled 3.7 parts per million (ppm) throughout the study, but increased to > 10 ppm by 60 min and remained elevated in lactose-intolerant subjects. Breath methane in normal children averaged 1.6 ppm from 0 to 120 min. In contrast, CH4 excretion by lactose-intolerant children averaged 5.1 ppm at 90 min; and, by 120 min levels increased significantly compared with control. Breath methane levels in lactose-intolerant subjects following a lactose load continued to increase, however, despite the coingestion of exogenous lactase in amounts calculated to result in complete hydrolysis of the disaccharide. These data demonstrate that lactase-deficient children manifest significant increases in breath methane excretion following lactose ingestion and that enhanced methane production may be a consequence of several factors, including altered fecal pH and increased methanogenic substrates provided by colonic lactose fermentation. Further studies are required to determine the clinical significance of elevated methane production in lactose intolerance.