Lactose malabsorption and intolerance in the elderly

BACKGROUND

Lactase activity declines with age in rats, but it is not clear whether this model is also shared by humans. Few studies have evaluated lactose intolerance and malabsorption in the elderly and no definite conclusions can be drawn. The aim of our study was therefore to verify the impact of age on lactose intolerance and malabsorption.

METHODS

Eighty-four healthy subjects took part in the study. Thirty-three were <65 years, 17 were between 65 and 74 years and 34 were >74 years. All the subjects underwent a preliminary evaluation of intestinal gas production capacity and oro-cecal transit time by H2/CH4 breath test after lactulose. After a 3-day period, an H2/CH4 breath test after lactose was performed. The occurrence of intolerance symptoms during the test and in the 24 h after the test was recorded.

RESULTS

Breath H2 and CH4 excretion parameters at fasting and after lactulose did not differ between the three groups. Cumulative breath H2 excretion after lactose was higher in subjects >74 years than in subjects <65 years and in subjects aged 65-74 years, while no difference was found between the latter two groups. In subjects >74 years, the prevalence of lactose malabsorption was higher than in the other two groups, while no significant difference was observed between subjects <65 years and subjects aged 65-74 years. Within the malabsorber subjects, the prevalence of lactose intolerance was higher in subjects <65 years than in those aged 65-74 years and in those aged >74 years. No significant difference was found between the latter two groups. No difference was found between the three groups in terms of daily calcium intake and a significant negative correlation between symptom score and daily calcium intake was only found in the group of subjects aged <65 years.

CONCLUSIONS

As age increases, the prevalence of lactose malabsorption shows an increase while the prevalence of intolerance symptoms among malabsorbers shows a decrease. Accordingly, daily calcium intake was similar among the adults and elderly studied.

Non-absorbable antibiotics for managing intestinal gas production and gas-related symptoms

BACKGROUND

Simethicone, activated charcoal and antimicrobial drugs have been used to treat gas-related symptoms with conflicting results.

AIM

To study the relationship between gaseous symptoms and colonic gas production and to test the efficacy of rifaximin, a new non-absorbable antimicrobial agent, on these symptoms.

METHODS

Intestinal gas production was measured by hydrogen (H2) and methane (CH4) breath testing after lactulose in 21 healthy volunteers and 34 functional patients. Only the 34 functional patients took part in a double-blind, double-dummy controlled trial, receiving, at random, rifaximin (400 mg b.d per 7 days), or activated charcoal (400 mg b.d per 7 days). The following parameters were evaluated at the start of the study and 1 and 10 days after therapy: bloating, abdominal pain, number of flatus episodes, abdominal girth, and cumulative breath H2 excretion.

RESULTS

Hydrogen excretion was greater in functional patients than in healthy volunteers. Rifaximin, but not activated charcoal, led to a significant reduction in H2 excretion and overall severity of symptoms. In particular, in patients treated with rifaximin, a significant reduction in the mean number of flatus episodes and of mean abdominal girth was evident.

CONCLUSIONS

In patients with gas-related symptoms the colonic production of H2 is increased. Rifaximin significantly reduces this production and the excessive number of flatus episodes.

Quality control study of H2 breath testing for the diagnosis of carbohydrate malabsorption in Italy. The "Tenue Club" Group

BACKGROUND AND AIMS

H2 breath testing is increasingly used in Italy. The aim of this multicenter study was to assess the accuracy of this technique in the diagnosis of carbohydrate malabsorption.

METHODS

An anonymous questionnaire was used to collect information about H2 breath testing methods and to design the quality control study. Fifteen out of 23 laboratories responded to the questionnaire and 12/23 completed the entire study.

RESULTS

The survey revealed that a large variety of H2 testing methods are employed in Italy, but none have been previously tested for accuracy. This prospective study showed that these tests fail to identify > 20% of patients with malabsorption. In contrast, a new method based on single H2 breath measurement at 6 hours after lactulose ingestion and a cutoff value of greater than 5 ppm, had a sensitivity of 92% +/- 4% and a specificity of 94% +/- 0.5%. Increasing the cut-off to 10 ppm resulted in a sensitivity of 88% +/- 9% and a specificity of 100%. This improved accuracy was obtained with a much simpler testing procedure in which only one breath sample is analyzed, in contrast to the baseline and multiple subsequent samples that are analyzed using the currently employed techniques.

CONCLUSIONS

A great improvement in the accuracy of the H2 breath test, as well as a considerable saving in terms of time and costs, may be possible through the use of a new, simplified H2 breath test followed by careful H2 analysis.

Measurements of the jejunal unstirred layer in normal subjects and patients with celiac disease

Normal intestinal absorption of nutrients requires efficient luminal mixing to deliver solute to the brush border. Lacking such mixing, the buildup of thick unstirred layers over the mucosa markedly retards absorption of rapidly transported compounds. Using a technique based on the kinetics of maltose hydrolysis, we measured the unstirred layer thickness of the jejunum of normal subjects and patients with celiac disease, as well as that of the normal rat. The jejunum of humans and rats was perfused with varying maltose concentrations, and the apparent Michaelis constant (Km) and maximal velocity (Vmax) of maltose hydrolysis were determined from double-reciprocal plots. The true Km of intestinal maltase was determined on mucosal biopsies. Unstirred layer thickness was calculated from the in vivo Vmax and apparent Km and the in vitro Km of maltase. The average unstirred layer thickness of 11 celiac patients (170 micron) was seven times greater than that of 3 controls (25 micron). The unstirred layer of each celiac exceeded that of the controls. A variety of factors could account for the less efficient luminal stirring observed in celiacs. Although speculative, villous contractility could be an important stirring mechanism that would be absent in celiacs with villous atrophy. This speculation was supported by the finding of a relatively thick unstirred layer (mean: 106 micron) in rats, an animal that lacks villous contractility. Because any increase in unstirred layer slows transport of rapidly absorbed compounds, poor stirring appears to represent a previously unrecognized defect that could contribute to malabsorption in celiac disease and, perhaps, in other intestinal disorders.

Lactose intolerance and bone mass in postmenopausal Italian women

Previous studies on the role of lactose malabsorption in the pathogenesis of postmenopausal osteoporosis have yielded conflicting results and further information is needed. To date, all studies have been carried out on populations with a low prevalence of lactose malabsorption and the lactose intestinal absorptive capacity was tested using a non-physiological dose of lactose. In fifty-eight Italian postmenopausal women (mean age 57 (SD 7) years), bone mineral density (BMD) at lumbar spine, H2 breath response after ingestion of 20 g lactose, intensity of symptoms of intolerance after a lactose load and daily Ca intake were evaluated. No differences were found between women with or without a positive H2 breath test with regard to BMD (-1.2 (SD 0.9) v. -0.9 (SD 0.8)) and Ca intake (509 (SD 266) v. 511 (SD 313) mg/d). On the contrary, both BMD and Ca intake were significantly lower in women with lactose malabsorption and symptoms of intolerance (-1.5 (SD 0.7) and 378 (SD 220) mg/d) than in those with malabsorption without symptoms (-0.9 (SD 0.9) and 624 (SD 254) mg/d). Moreover, in lactose malabsorbers Ca intake was correlated inversely with symptom score (rs -0.31, P < 0.05) and positively with BMD (rs 0.42, P < 0.005). Our results show that in Italian postmenopausal women Ca intake and BMD are not influenced directly by lactose malabsorption; the appearance of symptoms of intolerance seems to influence BMD unfavourably through a reduced Ca intake.

The possible role of breath methane measurement in detecting carbohydrate malabsorption

To evaluate the possibility that measurement of breath methane (CH4) enhances the accuracy of breath hydrogen (H2) testing to diagnose carbohydrate malabsorption, breath CH4 concentration of healthy subjects was studied. Fasting breath CH4 concentration measured three times over a 30-minute period in 44 CH4-producing volunteers ranged from 5 to 120 ppm. Fluctuation of breath CH4 excretion exceeded 100% increase over fasting in 1 of 9 subjects who ingested a nonabsorbable, carbohydrate-free solution. Out of 13 subjects who had a false negative breath H2 response to lactulose, 11 had a CH4 percentage increase greater than 100%. In 11 of 32 lactose-intolerant patients with a negative breath H2 test, CH4 percentage increase after lactose challenge was greater than 100%. These data suggested that in methanogenic individuals, breath CH4 measurement might enhance the accuracy of H2 breath testing in detecting carbohydrate malabsorption.

Methanogens outcompete sulphate reducing bacteria for H2 in the human colon

Methanogens and sulphate reducing bacteria compete for H2 in the human colon, and, as a result, faeces usually contain high concentrations of just one of these two organisms. There is controversy over which of these organisms wins the competition for H2, although theoretical data suggest that sulphate reducing bacteria should predominate. To elucidate this question experiments were undertaken in which sulphate enriched homogenates of human sulphate reducing faeces and methane producing faeces were incubated separately or mixed together. Co-incubation of sulphate reducing faeces with methanogenic faeces resulted in a sixfold reduction in the activity of the sulphate reducing bacteria (measured as sulphide production), whereas methane production was not inhibited by co-incubation with sulphate reducing bacteria. Methanogenic faeces also consumed H2 more rapidly and reduced the H2 tension of the homogenate to a lower value than did sulphate reducing faecal samples. In these experiments, methanogens seem to outcompete sulphate reducing bacteria for H2.

Study of constancy of hydrogen-consuming flora of human colon

The constancy of the hydrogen consuming flora of the human colon was studied in 15 healthy subjects via two measurements obtained 18 to 36 months apart. Hydrogen disappearance rate and the major products of H2-consuming bacteria, methane and sulfide, were measured during incubation of fecal homogenates with excess hydrogen and sulfate. In 11/15, the hydrogen consumption rate and the predominant hydrogen-consuming pathway (methanogenesis, sulfate reduction, or neither) remained constant. However, major shifts in these pathways were observed in four subjects, with two losing and two gaining the ability to produce methane. Methanogenesis was associated with the highest hydrogen consumption rate. This study demonstrates that clinically unrecognizable, major alterations of the colonic flora occur in healthy subjects. Understanding of the factors responsible for these alterations might allow for therapeutic manipulation of the colonic flora.

Detection of malabsorption of low doses of carbohydrate: accuracy of various breath H2 criteria

BACKGROUND

Although the accuracy of breath H2 testing to detect malabsorption of small (< 50 g) doses of carbohydrate has never been evaluated, studies suggest that its accuracy is limited by a high prevalence of "H2 nonproducers." The aim of this study was to determine the accuracy of H2 breath testing in the detection of malabsorption of 10 g of carbohydrate.

METHODS

In 55 healthy subjects, we determined the ability of breath H2 measurements to distinguish between the ingestion of 10 g of a nonabsorbable carbohydrate (lactulose) and two control meals, a nonabsorbable electrolyte solution or glucose (10 g).

RESULTS

The conventional criterion of a 20 ppm increase in breath H2 had 100% specificity but failed to identify lactulose malabsorption in 47% and 24% of subjects at 4 and 8 hours of testing. In contrast, a breath H2 of > 6 ppm at 5 or 6 hours had near perfect specificity and sensitivity. A sum of breath H2 at 5, 6, and 7 hours of > 15 ppm yielded perfect separation between lactulose and control solutions.

CONCLUSIONS

True "H2 nonproducers" are extremely rare. Using appropriate criteria, breath H2 testing provides a very accurate means of identifying malabsorption of low doses of carbohydrate.

Prevalence and consistency of low breath H2 excretion following lactulose ingestion. Possible implications for the clinical use of the H2 breath test

The clinical use of the H2 breath test is limited by the finding that a variable fraction of the population fails to excrete appreciable H2 during colonic carbohydrate fermentation. Therefore, we assessed the ability to increase breath H2 excretion in 371 patients (224 female, 147 male) by administering the nonabsorbable sugar lactulose. Following 12g of lactulose, 27% of 94 patients did not increase their breath H2 concentration over 20 ppm and were considered low H2 excretors. Ingestion of 20 g of lactulose in 277 patients yielded a frequency of low H2 excretors of 14%. Six of 10 patients that were low H2 excretors after 12g of lactulose increased their breath H2 levels over 20 ppm when tested with 20g. In 35 patients tested with the same amount of lactulose on two separate occasions, the subject frequently altered his or her H2 producing status over a period of a few weeks. Low H2 excretors had a significantly higher breath CH4 concentration, both fasting (22 +/- 34 ppm) and after lactulose (51 +/- 58 ppm) compared to the remaining patients (5 +/- 13 ppm and 16 +/- 40 ppm, respectively). While the mean age of low excretors (54 +/- 17 years) was significantly higher than the others (44 +/- 17 years), no difference was found for sex prevalence and stool pH. This study demonstrates that respiratory H2 excretion following lactulose ingestion is not consistent and suggests that the application of too restrictive criteria could lead to improper interpretation of the H2 breath test.

Use of metabolic inhibitors to study H2 consumption by human feces: evidence for a pathway other than methanogenesis and sulfate reduction

Human fecal bacteria produce and consume hydrogen, and consumption rate is a critical determinant of the volume of H2 liberated into the colonic lumen. Two bacterial reactions that have been reported to be major consumers of H2 are methanogenesis and sulfate reduction. To determine the importance of each of these reactions, we measured the disappearance of exogenous H2 during incubation with human fecal homogenates treated with 20 mmol/L 2-bromoethanesulphonic acid (BES), an inhibitor of methanogenesis, and/or 20 mmol/L sodium molybdate (Mo), an inhibitor of sulfate reduction. Four methanogenic and four nonmethanogenic samples consumed an average of 99% and 85%, respectively, of the initial H2 during 22 hours of incubation. With methanogenic homogenates, 36% of the H2 consumption persisted despite inhibition of methanogenesis. Inhibition of sulfate reduction had no effect on the rate of H2 consumption by these eight fecal specimens. The importance of fecal sulfate availability was determined in fecal samples obtained from an additional 14 randomly selected volunteers. Incubation after supplementation with 20 mmol/L sulfate was associated with an increase in sulfide production in four of the samples, and three of these four samples also demonstrated an increased rate of H2 consumption. No such evidence of sulfate reduction was observed in the other 10 homogenates. We conclude that a bacterial reaction other than methanogenesis and sulfate reduction, perhaps the recently described reduction of CO2 to acetate, represents a major metabolic route of H2 disposal in nonmethanogenic feces and a minor, but appreciable, pathway in methanogenic feces.

Non-absorbable antibiotics and small bowel bacterial overgrowth

The normal gastrointestinal flora includes no more than 10(3) organisms/ml of gastric aspirate and no more than 10(5) organisms/ml of duodenal or jejunal juice. The organisms are primarily gram-positive and aerobic bacteria. In particular anatomical or functional predisposing conditions, an abnormal colonization takes place in the small bowel with microbial concentrations > or = 10(7)/ml of aspirate and with a predominance of anaerobes and coliforms. At times this small bowel bacterial overgrowth remains asymptomatic, but more often leads to a true malabsorption syndrome with symptoms, such as diarrhoea, weight loss and megaloblastic anemia. The most accurate procedure for confirming the presence of this condition is represented by the bacterological analysis of the jejunal aspirate. The routine use of this method is, however, notably hindered by the need for intubation of the patient and by the lack of laboratories suitably equipped for anaerobe culture. As an alternative to this complex procedure, numerous non-invasive tests have been perfected over the last few years, including the glucose- or lactulose- H2 breath test. The main aim of the treatment of the small bowel bacterial overgrowth is the suppression of the bacterial colonization using antimicrobial therapy. Among the local-action non-absorbable antibiotics, rifaximin, was shown to have bactericidal activity against aerobes and anaerobes bacteria, such as bacteroides, lactobacilli and clostrides. In controlled clinical trials the antibiotic has demonstrated therapeutic efficacy in bacterial origin diarrhoea, in porto-systemic encephalopathy, in diverticulosis and, finally, in small bowel bacterial overgrowth.

A simple carbon monoxide breath test to estimate erythrocyte turnover

Carbon monoxide is stoichiometrically released when heme is converted to bilirubin. This report describes and validates a novel technique that permits the estimation of heme turnover and red blood cell survival from the carbon monoxide concentration of end-expiratory breath samples. The end-alveolar Pco of a subject was corrected for environmental carbon monoxide exposure with a simple device that equilibrates with atmospheric carbon monoxide at the same rate as does the subject. The resultant value (endogenous Pco) was tested for its ability to predict heme turnover and red blood cell survival. Red cell survival times of 32 healthy subjects, as calculated from the endogenous Pco, averaged 101 +/- 19 days, a value close to the expected 110-day survival time; 13 patients with clinical evidence of shortened red blood cell survival times had measured erythrocyte life spans ranging from 10 to 59 days. The endogenous Pco of each of seven patients increased after red blood cell transfusion, demonstrating that this technique detected the known rapid turnover of a small fraction of transfused cells. A good correlation (r = 0.91) was observed between heme turnover calculated from endogenous Pco and total fecal biliary pigment output. Carbon monoxide measurements reflect red blood cell destruction in both the marrow and the circulation, therefore yielding shorter life spans than did chromium 51 survival studies. This breath test appears to yield a rapid, semiquantitative assessment of heme turnover and red blood cell survival that is not provided by any other presently available technique. This simple, noninvasive carbon monoxide breath test may find widespread use in the evaluation of anemia and jaundice.

Factors affecting hydrogen production and consumption by human fecal flora. The critical roles of hydrogen tension and methanogenesis

We studied the influence of hydrogen tension (PH2) and methanogenesis on H2 production and consumption by human fecal bacteria. Hydrogen consumption varied directly with PH2, and methanogenic feces consumed H2 far more rapidly than did nonmethanogenic feces. At low PH2, H2 production greatly exceeded consumption and there was negligible accumulation of the products of H2 catabolism, methane and sulfide. Thus, incubation at low PH2 allowed the first reported measurements of absolute as opposed to net H2 production. Feces incubated at high and intermediate PH2 had a net H2 production of only 1/900 and 1/64 of absolute production. Glucose fermentation by fecal bacteria yielded an absolute H2 production of 80 ml/g, a value far in excess of that excreted by volunteers ingesting lactulose. We conclude that most H2 produced by colonic bacteria is consumed and methanogenesis and fecal stirring (via its influence on fecal PH2) are critical determinants of H2 consumption and, hence, net H2 production. Study of fecal samples from four subjects with low breath H2 excretion after lactulose showed that absolute H2 production was normal, and the low H2 excretion apparently reflected increased consumption due to rapid methanogenesis (two subjects) and decreased luminal stirring (two subjects).

Human jejunal unstirred layer: evidence for extremely efficient luminal stirring

Previous studies employing the osmotic transient technique have suggested that the human jejunal lumen is poorly stirred with a resultant unstirred layer thickness of approximately 600 microns. However, assuming negligible epithelial resistance to glucose absorption, we recently estimated that the unstirred layer thickness seemingly could not exceed 48 microns in the human jejunum. Because disaccharidases are located on the brush border, the rate of disaccharide hydrolysis can be used to determine unstirred layer thickness, independent of epithelial transport. In the present report, we utilized published hydrolysis data for sucrose and maltose to calculate the unstirred layer thickness in the normal human jejunum. This calculation indicated that the unstirred layer thickness was only approximately 35 microns, less than one-fifteenth of previously reported 600-microns values obtained with the osmotic transient technique. Diffusion through a 600-microns unstirred layer would be the rate-limiting step in absorption of all rapidly transported compounds. In contrast, with a 35-microns unstirred layer, variations in epithelial function or luminal stirring could readily influence the absorption.

beta-Galactosidase from Aspergillus niger in adult lactose malabsorption: a double-blind crossover study

An assessment was made of the efficacy of a beta-galactosidase, obtained from Aspergillus niger and added to intact milk, in decreasing lactose malabsorption and intolerance. Sixteen adult patients with malabsorption and intolerance to this sugar were studied in a double-blind crossover study vs. placebo. A 5-hour hydrogen breath test was used to assess malabsorption of lactose contained in 400 ml milk. When compared with placebo, the addition of exogenous lactase to intact milk caused a statistically significant reduction in the maximum breath H2 concentration (P less than 0.01) and in the cumulative H2 excretion (P less than 0.005). In the same way, the cumulative index for gastrointestinal intolerance was significantly lower (P less than 0.005) after the ingestion of lactase-added milk. This study demonstrates that enzyme replacement therapy, with beta-galactosidases obtained from Aspergillus niger, is effective in decreasing lactose malabsorption and its consequent intolerance in adult subjects with lactase deficiency.

Competition for hydrogen by human faecal bacteria: evidence for the predominance of methane producing bacteria

Studies of sludge have shown that some species of sulphate reducing bacteria outcompete methane producing bacteria for the common substrate H2. A similar competition may exist in human faeces where the methane (CH4) producing status of an individual depends on the faecal concentration of sulphate reducing bacteria. To determine if non-methanogenic faeces outcompete CH4 producing faeces for H2, aliquots of each type of faeces were incubated alone or mixed together, with or without addition of 10% H2 and/or 20 mmol/l sulphate. Methane producing faeces consumed H2 significantly more rapidly and reduced faecal H2 tension to a lower value compared with non-methanogenic faeces. The mixture of the two types of faeces yielded significantly more CH4 than CH4 producing faeces alone (mean (SD) 8.5 (1.3) v 2.9 (0.45) mmol/l of homogenate per 24 hours, p less than 0.01). Faecal sulphide concentrations were similar in CH4 producing and non-producing homogenates both before and after 24 hours of incubation. The addition of sulphate to the homogenates did not significantly influence CH4 production or sulphide formation. Our results suggest that in human faeces methane producing bacteria outcompete other H2 consuming bacteria for H2.

A reappraisal of the magnitude and implications of the intestinal unstirred layer

Until recently, a variety of studies had suggested that luminal stirring in the jejunum is relatively poor, with unstirred layers of about 600 microns reported for humans and 300-900 microns for animals. Unstirred layers of this magnitude would markedly retard the absorption of all solutes, and diffusion through this layer would be the rate-limiting step in the uptake of all rapidly absorbed compounds. As a result, luminal stirring, rather than epithelial transport, would be the major variable influencing absorption rate. However, recent studies in dogs and humans have shown that the unstirred layer has a maximal apparent thickness of only about 40 microns. This layer is far thinner than what can be achieved in vitro with vigorous stirring with a magnetic bar, suggesting that some unique stirring mechanism, perhaps villous contractions, is responsible for this extraordinarily efficient mixing. A 40-microns unstirred layer would produce only about 1/15 the resistance of the previously reported 600 microns value; with this thinner layer, alterations in either luminal stirring or epithelial function could readily influence the absorption rate of rapidly transported compounds.

Reproducibility of measurements of trace gas concentrations in expired air

Measurement of the pulmonary excretion of trace gases has been used as a simple means of assessing metabolic reactions. End alveolar trace gas concentration, rather than excretory rate, is usually measured. However, the reproducibility of this measurement has received little attention. In 17 healthy subjects, duplicate collections of alveolar air were obtained within 1 minute of each other using a commercially available alveolar air sampler. The concentrations of hydrogen, methane, carbon monoxide, and carbon dioxide were measured. When the subject received no instruction on how to expire into the device, a difference of 28% +/- 19% (1SD) was found between duplicate determinations of hydrogen. Instructing the subjects to avoid hyperventilation or to inspire maximally and exhale immediately resulted in only minor reduction in variability. However, a maximal inspiration held for 15 seconds before exhalation reduced the difference to a mean of 9.6% +/- 8.0%, less than half that observed with the other expiratory techniques. Percentage difference of methane measurements with the four different expiratory techniques yielded results comparable to those obtained for hydrogen. In contrast, percentage differences for carbon monoxide measurements were similar for all expiratory techniques. When normalized to a PCO2 of 5%, the variability of hydrogen measurements with the breath-holding technique was reduced to 6.8% +/- 4.7%, a value significantly lower than that obtained with the other expiratory methods. This study suggests that attention to the expiratory technique could improve the accuracy of tests using breath hydrogen measurements.

Measurement of starch absorption in humans

Although starch provides a large fraction of human caloric intake, there is limited information concerning the efficiency of intestinal absorption of this nutrient. Owing to the fermentation of starch by colonic bacteria, there is no quantitative test for starch absorption comparable to the fecal fat determination. The most accurate estimation of starch absorption has been obtained by intubating the terminal ileum and aspirating ileal contents following ingestion of a meal containing starch plus a nonabsorbable marker. Starch absorption is calculated from the ratio of starch:marker in the ileal aspirate relative to the ratio in the meal. Disadvantages of the technique are the requirement for ileal intubation and the possible adverse effect of intubation on the absorptive process. A more widely used technique to assess starch absorption involves measurement of breath hydrogen (H2) excretion after ingestion of starch. Malabsorbed starch is fermented by colonic bacteria with liberation of H2 that is absorbed and excreted in expired air. This test is simple and noninvasive and can provide quantitative measurements of starch malabsorption. Application of this technique has demonstrated that 5-10% of starch in wheat, potatoes, and corn is not absorbed by healthy subjects, while rice starch is nearly completely absorbed.

Where does serum amylase come from and where does it go?

The serum amylase concentration reflects the balance between the rates of amylase entry into and removal from the blood. Hyperamylasemia can result either from an increased rate of entry of amylase into the circulation and/or a decreased metabolic clearance of this enzyme. The pancreas and salivary glands have amylase concentrations that are several orders of magnitude greater than that of any other normal tissue, and these two organs probably account for almost all of the serum amylase activity in normal persons. A variety of techniques are now available to distinguish pancreatic from salivary-type isoamylase. Pancreatic hyperamylasemia results from an insult to the pancreas, ranging from trivial (cannulation of the pancreatic duct) to severe (pancreatitis). In addition, loss of bowel integrity (infarction or perforation) causes pancreatic hyperamylasemia due to absorption of amylase from the intestinal lumen. Hyperamylasemia due to salivary-type isoamylase is observed in conditions involving the salivary glands. In addition, this type of hyperamylasemia occurs in conditions in which there is no clinical evidence of salivary gland disease, such as chronic alcoholism, postoperative states (particularly postcoronary bypass), lactic acidosis, anorexia nervosa or bulimia, and malignant neoplasms that secrete amylase. Hyperamylasemia can also result from decreased metabolic clearance of amylase due to renal failure or macroamylasemia (a condition in which an abnormally high-molecular-weight amylase is present in the serum). Patients with abdominal pain and a markedly elevated serum amylase (more than three times the upper limit of normal) usually have acute pancreatitis, and additional serum enzyme testing is not helpful. Patients with smaller elevations of serum amylase often have conditions other than pancreatitis, and measurement of a serum enzyme more specific for the pancreas (pancreatitic isoamylase, lipase or trypsin) is frequently of diagnostic value in such patients.

Physiological measurements of luminal stirring in the dog and human small bowel

The resistance to absorption resulting from poor stirring of luminal contents (RLum) is considered to be equivalent to an unstirred layer of greater than 600 microns in the human small intestine. We measured RLum in the jejunum of conscious dogs by assessing the absorption rate of two rapidly absorbed probes, glucose, and [14C]warfarin. When RLum was expressed as an unstirred layer, the maximal thickness of the unstirred layer (assuming negligible epithelial cell resistance) was only approximately 35 and 50 microns for perfusion rates of 26 and 5 ml/min, respectively. Maximal unstirred layer thickness for the human jejunum, calculated from previous studies of glucose absorption, yielded a mean value of only 40 microns (range: 23 to 65 microns). Since epithelial resistance appears to be negligible during absorption of low concentrations of glucose, the maximal unstirred layer of 40 microns should be close to the true value for glucose in the human small intestine. We conclude that the unstirred layer for rapidly absorbed compounds in dogs and man are less than one-tenth of previously reported values, but this layer still may remain the rate limiting step in absorption of rapidly transported compounds.

Colonic concentrations of hydrogen and methane following colonoscopic preparation with an oral lavage solution

Explosions are a rare complication of electrocautery in the colon. The cause of these explosions is ignition of gas containing hydrogen (greater than 4%) or methane (greater than 5%), and oxygen. Hydrogen and methane are products of colonic bacterial metabolism. Oral solutions used for colonoscopy preparation are designed to cleanse the colonic lumen but provide no substrate for fermentation reactions. In 52 patients undergoing colonoscopy, gas samples were collected from the right, transverse, and left colon and analyzed for hydrogen, methane, oxygen, and carbon dioxide. The highest hydrogen and methane concentrations were 0.6% and 0.7%, respectively, less than 16% of the explosive level. Oxygen and carbon dioxide concentrations were close to those of air, suggesting that the bulk of colonic gas was air infused during the procedure. We conclude that the concentrations of explosive gases are well below the hazardous levels when oral colonic cleansing solutions and standard colonoscopic procedures are employed.

Methodology of the H2 breath test. II. Importance of the test duration in the diagnosis of carbohydrate malabsorption

We analyzed the results of 352 consecutive four-hour lactose hydrogen breath tests with the aim of verifying whether the results after two hours have the same accuracy as those after four hours in the diagnosis of malabsorption of 20g of lactose. Our results show that in 208 subjects who proved to be lactose malabsorbers the mean changes in breath H2 concentration were higher at three and a half hours than at any other time. Moreover, although the majority of the subjects (63%) reached the cut-off value (more than 20 parts per million with respect to the baseline value) in the first two hours of the test, in 76 of our 208 lactose malabsorbers (37%) a hydrogen increase higher than the cut-off value is only detectable after the second hour of the test. Therefore, unlike those who believe that two samples of expired air at 0 time and after two hours are sufficient, we think that for greater diagnostic accuracy the lactose H2 breath test must be prolonged for at least 4 hours.

Methodology of the H2 breath test. I. Collection and storage for gas measurement

The measurement of hydrogen and methane in expired air is widely used in the field of gastrointestinal diagnosis. Techniques as simple and as reliable as possible are therefore requested for the collection and storage of breath samples. As far as collection is concerned, we compared three systems of end-expiratory sampling: a modified Haldane-Priestley tube, a Y-piece device fitted to a plastic syringe and a commercially available two-bag system. There was a significant correlation between the results obtained with all three systems, suggesting that all are sufficiently reliable. However, the two-bag system does not require particular training on behalf of the operator or particular cooperation from the patients and also makes it possible to take samples from more than one patient at the same time. For the storage of breath samples plastic syringes are the most commonly used device. Nonetheless, at room temperature there is a leakage of hydrogen equal to 9% after 24 hours, increasing to 29% after 5 days of storage. Refrigeration of the syringes at -20 degrees C prevents any loss in the first 48 hours and limits it to 5% after 5 days. The stability of the methane was higher than that of the hydrogen: after 5 days the loss is 4% at room temperature and 2% at -20 degrees C. For both gases the losses increase significantly at a temperature of 37 degrees C and are not affected by the initial concentration of the stored gas.(ABSTRACT TRUNCATED AT 250 WORDS)

The diagnosis of small bowel bacterial overgrowth. Reliability of jejunal culture and inadequacy of breath hydrogen testing

The reliability of a single jejunal culture in the diagnosis of small bowel bacterial overgrowth has recently been questioned. Seventy-seven patients thought to have bacterial overgrowth, defined as a jejunal culture yielding at least 10(6) organisms per milliliter of aspirate, took part in the study. Bacterial overgrowth was found in 74% of the patients with predisposing conditions and in 32% of those with no clear causes of bacterial colonization. The intestinal juice of some patients was taken at two different levels of the proximal jejunum, using both the closed- and open-tube systems. Highly significant correlations (rs = 0.90, p less than 0.001) were found between the numbers of bacteria per milliliter at the 2 jejunal levels and between the numbers of bacteria per milliliter of jejunal aspirate obtained from the closed and open tubes (rs = 0.84, p less than 0.001). Compared with the jejunal culture, the gas chromatography of volatile fatty acids in jejunal aspirate and the glucose- and lactulose-hydrogen breath tests showed sensitivities of 56%, 62%, and 68% and specificities of 100%, 83%, and 44%, respectively. This work demonstrates the reliability of jejunal cultures and the inadequacy of breath hydrogen testing in the prediction of positive jejunal cultures. When results of testing for volatile fatty acids in jejunal aspirates are positive, this always indicates the presence of bacterial overgrowth; thus, this procedure would avoid the more complicated, time-consuming, and costly bacteriological analysis of jejunal samples.

Diamine oxidase plasma activities after treatment with heparin and jejunal morphometry in untreated coeliac disease

Diamine oxidase plasma concentrations after treatment with heparin were measured and compared with the surface to volume ratio of jejunal biopsy samples assessed by a morphometric technique in patients with untreated and treated coeliac disease and in biopsied controls. As expected, enzyme activity was significantly lower in patients with untreated coeliac disease than in patients on a gluten-free diet and in biopsied controls. No difference was found between treated patients and biopsied controls. There was a significant overall correlation between plasma enzyme activity and surface to volume ratio of jejunal mucosa, although two untreated patients without an overt malabsorption syndrome but with a very low surface to volume ratio had normal enzyme activity. This study shows that in coeliac disease plasma diamine oxidase activity after treatment with heparin does not always mirror the extent of the jejunal lesions, particularly in those patients with minimal or unrelated symptoms who would benefit most from a valid screening test to identify their condition.

Decreased plasma postheparin diamine oxidase levels in celiac disease

The highest diamine oxidase activity is contained in small-bowel mucosa and, after heparin administration, the enzyme is released by the intestine into the plasma. Previous experimental studies showed that measurement of plasma postheparin diamine oxidase activity is a sensitive test for quantitating the length and severity of small-bowel mucosal injury. On this basis, we measured plasma diamine oxidase activity in celiac disease, a condition characterized by a loss of mature enterocyte mass. Twenty-five untreated celiac patients, 21 celiac patients on a gluten-free diet, 16 patients with small-bowel diseases other than celiac disease (abnormal controls), and 18 healthy controls were studied. Diamine oxidase activity was measured using [14C]putrescine as substrate and expressed as units per milliliter of plasma. Basal diamine oxidase levels in controls and patients were too low for significant differences between the groups to be detected. After preliminary experiments in which, on separate occasions, heparin was intravenously administered at doses of 75 and 150 units/kg and in which the second blood sample was taken 10 and 30 min after heparin injection, it was decided to use the 150 unit/kg dose and to measure plasma diamine oxidase activity in the blood sample taken 10 min after heparin stimulation in all the remaining subjects taking part in the study. Postheparin diamine oxidase levels were significantly lower in untreated celiac patients (mean 1.53 units/ml) than in healthy controls (mean 5.85), treated celiac patients (mean 4.82), and abnormal controls (mean 2.62). Except in three patients, no overlap between healthy controls and untreated celiac patients was observed. No significant difference was detected between healthy controls and treated celiac patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of small intestine bacterial overgrowth with rifaximin, a non-absorbable rifamycin

In twelve patients affected by small bowel bacterial overgrowth, diagnosed by means of the lactulose hydrogen breath test, the therapeutic efficacy of a non-absorbable derivative of rifamycin, rifaximin, was evaluated. This study showed that this drug has a satisfactory therapeutic efficacy in contaminated small bowel syndrome and, at the doses tested, is free of side-effects.

Sorbitol malabsorption in normal volunteers and in patients with coeliac disease

Sorbitol is a hexahydroxy alcohol used as a sugar substitute in many dietetic foods and as a drug vehicle. Previous studies have suggested that sorbitol ingestion may be an additional cause of non-specific gastrointestinal distress. We evaluated sorbitol malabsorption in 30 healthy volunteers, seven patients with untreated coeliac disease and nine patients with coeliac disease on a gluten free diet, using a four hour H2 breath test. After ingestion of test solutions containing sorbitol 10 and 20 g and of four sweets (6.8 g sorbitol), 90%, 100%, and 62% of healthy volunteers, respectively had significantly raised H2 excretion, indicating malabsorption of sorbitol. Of all healthy subjects tested, 45% after 10 g, 100% after 20 g, and 50% after four sweets complained of symptoms of carbohydrate intolerance during the eight hours after sorbitol. After a 5 g dose given at concentrations of 2%, 4%, 8%, 16%, malabsorption was shown in 10%, 12%, 22%, and 43% of the healthy volunteers. Symptoms of intolerance at 5 g were experienced only at concentrations of 8% and 16%. Unlike healthy volunteers and coeliac patients on a gluten free diet, 100% of untreated coeliacs malabsorbed a 2% solution of 5 g sorbitol. These results show that malabsorption and intolerance of sorbitol may result from ingestion of doses and/or concentrations usually found in many foods and drugs; they underline the need to consider this as a possible and hitherto underestimated cause of gastrointestinal symptoms.

Fasting breath hydrogen in celiac disease

We studied the possible clinical significance of high basal levels of H2 by analyzing the breath excreted by the following fasting subjects: 50 healthy volunteers, 149 subjects with functional bowel disorders, 16 patients with small bowel bacterial overgrowth proven by bacteriology, 34 patients with untreated celiac disease, 40 patients with celiac disease on a gluten-free diet, and 40 patients with disorders of the small intestine other than celiac disease (disease controls). The fasting levels of H2 in untreated celiac patients (mean 22.5 +/- 19.3 ppm) were significantly higher than those in healthy volunteers (5.8 +/- 3.1 ppm), patients with functional bowel disorders (6.6 +/- 4.4 ppm), treated celiac patients (9.9 +/- 8.1 ppm), and disease controls (7.0 +/- 6.7 ppm). No significant difference was found between patients with untreated celiac disease and bacterial overgrowth (mean 14.7 +/- 14.0 ppm). The percentage of patients with elevated H2 fasting levels in untreated celiac disease (58.8%) was significantly higher than that in the other groups, except for the patients with bacterial overgrowth (43.7%). In 14 celiac patients, studied before and after a gluten-free diet, fasting H2 levels decreased from 26.6 +/- 18 to 11.6 +/- 10 ppm, becoming normal only in those patients with healing of intestinal lesions. Our results show that high fasting H2 levels are a frequent feature of untreated celiac disease and that the return to normal of these levels is predictive of villous regrowth.

[Consumer available margarines in Italy. Note 1: Fatty acid composition and trans-isomers content (author's transl)]

The most used consumer available margarines in Italy, showed important differecens regarding composition of the saturated (S.F.A.) and trans-unsaturated (T.U.F.A.) fatty acids. The ratio S.F.A./U.F.A. correlated well to the T.U.F.A. content. The margarines with the higher U.F.A. values presented also the higher T.U.F.A. values and corresponded to those prepared from a single seed oil (peanut, corn, sunflower). The monounsaturated fatty acids are composed of a mixture of geometrical and positional isomers with the unsaturation at any C atom between C6 and C16.