Letter: Lactose feeding in lactose-intolerant monkeys.
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Animals↗
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Reinvestigation of lactose intolerant children: lack of correlation between continuing lactose intolerance and small intestinal morphology, disaccharidase activity, and lactose tolerance tests.
Thirty children on a lactose-free diet aged from 2-38 months who had previously been diagnosed as having secondary lactose intolerance were reinvestigated on 32 occasions by an oral lactose tolerance test, small intestinal biopsy, and measurement of disaccharidase activity in order to detect the presence of continuing lactose intolerance before reintroduction of milk. No correlation was found between continuing lactose intolerance, as diagnosed by the development of watery stools containing excess reducing substances after an oral load of lactose, and maximum blood glucose rise during a lactose tolerance test, lactase levels, and small intestinal morphology.
Child, Preschool↗
Lactose digestion from unmodified, low-fat and lactose-hydrolyzed yogurt in adult lactose-maldigesters.
The efficiency of carbohydrate absorption from two unmodified plain yogurts, a low-fat yogurt and a yogurt produced from lactose-hydrolyzed milk, was compared using the breath hydrogen response in 14 lactose-maldigesters. The maldigesters showed symptoms of intolerance to a standard 360 ml glass of milk containing 18 g lactose. Compared to intact milk, the breath hydrogen response to two varieties of unmodified yogurt and the lactose hydrolyzed yogurt was severely attenuated while the hydrogen response to low-fat yogurt was intermediate. Intolerance symptoms were significantly and equally reduced with all four yogurt products compared to milk. Ten lactose-digesters had a significantly greater efficiency of lactose digestion with 360 ml of milk than the 14 maldigesters; however, except for the magnitude of the maximum rise in breath H2, no inter-group differences were observed in response to unmodified yogurt. We conclude that lactose prehydrolysis adds nothing to the ability to tolerate and digest plain, full-fat yogurts, but it may be useful with low-fat or pasteurized varieties.
Adult↗
Evidence that the asparagine 322 mutant of the lactose permease transports protons and lactose with a normal stoichiometry and accumulates lactose against a concentration gradient.
The single asparagine 322 mutant of the lactose permease was made by constructing a hybrid plasmid which contained the amino-terminal coding sequence from the wild-type permease gene and the carboxyl-terminal coding sequence from a previously characterized double mutant permease which contained an asparagine residue at position 322. Since histidine at position 322 has been postulated to be critically involved with H+ transport and the active accumulation of sugars, the ability of the Asn-322 mutant to couple H+ and sugar transport was carefully examined. Measurements of proton/lactose stoichiometries gave very similar values for the wild-type (0.78) and the Asn-322 strain (0.82). Moreover, the Asn-322 mutant was able to effectively accumulate lactose against a concentration gradient although the levels of accumulation in the Asn-322 mutant (approximately 5-7-fold) were significantly less than that of the wild-type strain (approximately 30-40-fold). Overall, these results are inconsistent with the notion that an ionizable histidine residue at position 322 is obligatorily required for H+ transport or the active accumulation of galactosides against a concentration gradient. The ability of the Asn-322 mutant to recognize a variety of sugars was compared with wild-type, Val-177, and Val-177/Asn-322 strains. The Asn-322 mutant exhibited an ability to recognize and transport maltose (an alpha-glucoside) which was significantly better than the wild-type strain but not as good as either the single Val-177 mutant or the double Val-177/Asn-322 mutant. Both the Asn-322 and the Val-177/Asn-322 strain showed a relatively poor recognition for alpha-galactosides (i.e. melibiose), beta-galactosides (lactose and thiodigalactoside), and beta-glucosides (cellobiose). In contrast, the single Val-177 strain exhibited a normal recognition for these sugars.
Asparagine↗
Symptom response to lactose-reduced milk in lactose-intolerant adults.
The possible usefulness of low-lactose milk for those lactose-intolerant subjects who develop symptoms from milk consumption was investigated. In the first part of the study, 16 intolerant subjects (blood glucose rise less than 25 mg/100 ml) received low-lactose skim milk containing 15 g lactose (2.5 cups) and 7.5 g lactose (2.5 cups), regular skim milk containing 30 g lactose (2.5 cups), and all three milks plus a small breakfast. The low lactose milks produced significantly fewer symptoms. The food given with the milk had no significant effect on symptomatic response. The second group of 17 subjects received 25 g lactose in water (250 ml), skim milk (500 ml) and whole milk (500 ml); 10 g lactose in lactose-reduced skim (500 ml) and whole milk (500 ml) and whole milk (500 ml); and a placebo (250 ml). There was a significant positive relationship between amount of lactose consumed and symptom response. The form in which the lactose was administered (e.g., whole versus skim milk) was not significantly related to symptoms. It is concluded that in a symptomatic subjects a significantly greater quantity of low-lactose milk than regular milks can be consumed.
Adult↗
[Lactose--a potential dietary fiber. The regulation of its microecological effect in the intestinal tract. 2. The nutrient effect of lactose].
In the small intestine lactose is subjected to the hydrolytic impact of beta-galactosidase originating mainly from the mucosa. In rats about two thirds of the enzyme activity are located in the first part of the small intestine, and one third in the second one. A part of the mucosal enzyme does not remain in the mucosa. It becomes detached and can be determined in the chymus. The ratio of the transient to the resident proportion amounts to 1.8: 1 in germfree and 0.23: 1 in conventional rats. Bacterial settlement causes an increase in the mucosal mass resulting in higher total activity whereas the specific activity of the mucosal enzyme remains unchanged. Microorganisms occurring close to the small intestine mucosa take part in lactose degradation. Lactose-containing diet leads to an increase in both the bacterial and the mucosal activity, the latter one to varying degrees. Lactose concentration in the ileal chymus rises with increasing intake of lactose and decreasing protein and phosphate intake. Following a saturation kinetics the velocity of lactose hydrolysis is correlated with the lactose concentration of the diet. alpha-lactose is hydrolysed more rapidly in the small intestine of both human sucklings and rats than beta-lactose. As the results of a mathematical model show lactose mutarotation does not effect on the degree of lactose degradation in the small intestine. Depending on the intake of lactose and the food composition the rate of lactose hydrolysis amounts to: --max. 50% after small intestine perfusion in human sucklings, --max. 80% after small intestine perfusion in rats, --max. 60% in rats with ileostomata.
Animals↗
[Lactose content of the Danish diet. Study of lactose content of some ordinary Danish foodstuffs with reference to preparence of a dietary guide for patients with lactose malabsorption].
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Denmark↗
Estimation of the fraction of the lactose in a high lactose diet available for fermentation in the cecum and colon of the rat.
Experiments were conducted to determine the amount of lactose which passed into the large intestine and the lactase activity in the small intestine of rats (200 g) fed a control diet or a diet containing 30% lactose. The fraction of lactose consumed in a single 1-hour meal that escaped hydrolysis in the small intestine was estimated by measuring the area under a smooth curve of a plot of lactose:marker ratio in the terminal ileum expressed as a fraction of intake, against the fraction of the total marker that passed into the large intestine. This amounted to approximately 30% and 31.5% of the lactose consumed for the rats fed the control and 30% lactose diets, respectively. In another experiment in which the rats were fed a diet containing 30% lactose and the Cr-EDTA marker ad libitum for 1 week, approximately 43% of the lactose consumed became available for fermentation in the large intestine. This work suggests that a substantial fraction of the lactose ingested is available for fermentation in the large intestine. The lactase activity of homogenates of the small intestine of rats fed the control or high lactose diet was 106 +/- 5 or 115 +/- 4 mg lactose/30 minutes/rat (P less than 0.05), respectively. The lactase activity in the small intestine homogenate (mucosa + contents) was significantly higher than that actually available in vivo (110 +/- 7 versus 69 +/- 4 mg/30 minutes/rat).
Animals↗
Individual sensitivity to lactose in lactose malabsorption.
The clinical significance of lactose malabsorption and the individual sensitivity to lactose were investigated in 20 patients with verified lactose malabsorption. Thirteen patients were relieved of all symptoms while seven improved only on a lactose-free dth lactose-free milk but following provocation with increasing amounts of lactose, the tendency to diarrhea and abdominal discomfort increased considerably. Three patients experienced discomfort after provocation with only 5 gl lactose. On provocation with increasing amounts of lactose the seven patients who had not recovered also developed increased abdominal discomfort but none of them developed increased tendency to diarrhea. It is concluded that, in addition to lactose malabsorption, these patients must suffer from ittitable colon with tendency to constipation.
Abdomen↗
Effect of O-sulphate groups in lactose and N-acetylneuraminyl-lactose on their enzymic hydrolysis.
1. Lactose 6'-O-sulphate, N-acetylneuraminyl-(alpha 2 leads to 3)-D-lactose 6'-O-sulphate, N-acetylneuraminyl ?-O-sulphate-(alpha 2 leads to 3)-D-lactose 6'0-O-sulphate, N-acetylneuraminyl ?-O-sulphate-(alpha 2 leads to 6)-D-lactose and N-acetylneuraminyl-(alpha 2 leads to 3)- and -(alpha 2 leads to 6))-lactose 6'-O-sulphate were prepared by chemical sulphation of lactose, N-acetylneuraminyl-lactose and tis isomers by using pyridine-SO3 reagent. 2. Significant kinetic differences were observed in the enzymic hydrolysis of the sulphated derivatives compared with unsubstituted substrates. 3. In the case of reactions catalysed by rat liver lysosomal and Clostridium perfringens neuraminidases (EC 3.2.1.18), the presence of an O-sulphate group in the N-acetylneuraminyl moiety affected the reaction by decreasing the Km and the Vmax, its presence in the galactosyl moiety affected the reaction by decreasing the Km and increasing the Vmax. and its presence in both N-acetylneuraminyl and galactosyl moieties decreased the Km and the Vmax. of the reaction. 4. Mixed-substrate reaction kinetic data indicated competition between the sulphated and unsubstituted substrates for the same active sites on the neuraminidase molecule. 5. Lactose 6'-O-sulphate neither behaved as a substrate nor acted as an inhibitor with respect to unsubstituted lactose and p-nitrophenyl beta-D-galactopyranoside when tested with lactase of suckling rat intestine and Escherichia coli beta-D-galactosidase (EC 3.2.1.23). 6. Preliminary investigation also indicated that, whereas glucose 6-O-sulphate and glucose 3-O-sulphate were were neither substrate nor inhibitor of glucose oxidase (EC 1.1.3.4), galactose 6-O-sulphate was oxidized half as fast as unsubstituted galactose by galactose dehydrogenase (EC 1.1.1.48).
Animals↗
Colonization control of lactose-fermenting Salmonella typhimurium in young broiler chickens by use of dietary lactose.
Inclusion of lactose in the diets of chickens has been determined to reduce cecal colonization with Salmonella typhimurium. We hypothesized, therefore, that dietary lactose may be a practical means for reducing the prevalence of Salmonella contamination of chicken products. Because some strains of Salmonella are atypical and ferment lactose, we investigated the effects of dietary lactose on cecal colonization with lactose-fermenting S typhimurium. Broiler chicks were inoculated intracloacally with Lac+ S typhimurium selected for resistance to novobiocin and rifampicin. The chicks also were inoculated orally with certain anaerobes that do not effectively inhibit colonization by S typhimurium, but do appear essential for lactose mediated inhibition of cecal colonization. Control chicks were not given dietary lactose, and chicks in the experimental group were fed a diet containing 7% lactose. Enumeration of Lac+ S typhimurium in cecal contents revealed dietary lactose to be effective at controlling this organism. Control was correlated with changes in cecal pH and increases in undissociated volatile fatty acids, especially propionic acid.
Animals↗
Lactose digestion from yogurt: influence of a meal and additional lactose.
Lactose in yogurt is better digested than lactose in other dairy foods by lactase-deficient individuals, in part because of intraintestinal activity of yogurt microbial beta-galactosidase (beta-gal). The survival and activity of yogurt beta-gal depend on gastrointestinal transit, pH, and viability of the yogurt culture. To evaluate the ability of yogurt beta-gal to digest lactose when yogurt is consumed with food or with additional lactose, 22 healthy lactose-maldigesting individuals were fed 10 test meals. Results of breath-hydrogen expiration, incidence of symptoms, and enzyme and lactose content of gastric aspirates indicate that the consumption of a meal with yogurt does not inhibit, and may slightly improve, lactose digestion from yogurt. However, yogurt beta-gal appears unable to assist in the digestion of additional lactose beyond that normally present in yogurt.
Adult↗
Effect of a single dose of lactase on symptoms and expired hydrogen after lactose challenge in lactose-intolerant subjects.
The effect of a single dose or oral lactase on symptoms, breath hydrogen concentration, and glucose absorption in lactose-intolerant subjects challenged with lactose was studied. Volunteers underwent a lactose challenge test; those whose breath hydrogen concentrations increased 20 ppm or more and who met other criteria were admitted as subjects. After fasting, the subjects were given three chewable lactase tablets (total lactase dose, 9900 FCC units) or placebo tablets in a randomized, double-blind, crossover manner. The subjects also consumed 8 oz of whole milk in which 37.5 g of lactose powder was dissolved (total lactose content, 50 g). The washout period between lactose challenges was at least one week. Breath hydrogen and plasma glucose concentrations were measured before and at intervals after the challenges, and the subjects completed symptom-evaluation questionnaires every eight hours for four days. Twenty-four subjects completed the study. The maximum mean breath hydrogen concentration was significantly lower after lactase treatment than after placebo treatment. In 21 subjects, the area under the hydrogen concentration-time curve (AUC) was lower after lactase than after placebo; three subjects had hydrogen AUCs more than 300 ppm.hr lower. There were no significant differences in plasma glucose levels. Subjective ratings of the severity of abdominal cramping, belching, flatulence, and diarrhea were lower during the first eight hours after challenge in lactase-treated subjects; ratings for bloating were lower during the next eight hours. Single doses of a chewable lactase tablet reduced the concentration of expired hydrogen and symptoms of lactose intolerance after a lactose challenge.
Abdominal Muscles↗
Transport by the lactose permease of Escherichia coli as the basis of lactose killing.
Lactose killing is a peculiar phenomenon in which 80 to 98% of the Escherichia coli cells taken from a lactose-limited chemostat die when plated on standard lactose minimal media. This unique form of suicide is caused by the action of the lactose permease. Since uptake of either lactose or galactose by the lactose permease caused death, the action of rapid transport across the membrane must be the cause of the phenomenon. Alternative causes of lactose killing, such as accumulation of toxic metabolic intermediates or action of the beta-galactosidase, have been eliminated. It is proposed that rapid uptake of sugars by the lactose permease disrupts membrane function, perhaps causing collapse of the membrane potential.
Biological Transport↗
Gastric emptying of lactose and milk in subjects with lactose malabsorption.
Six lactose absorbers (LA) and 5 lactose malabsorbers (LM) had tests of gastric emptying with 750-ml meals of glucose in water, lactose in water, plain milk, and chocolate milk. The glucose and lactose meals emptied in a similar fashion in LA and LM subjects with a significant decrease in gastric emptying as the osmolarity of the meals was doubled. If the data are normalized by dividing lactose emptying by the emptying of glucose meals of twice the osmolality in each individual, the lactose malabsorbers empty significantly more lactose. Both LA and LM subjects emptied comparable amounts of milk meals having similar osmolarity. Chocolate milk, which had a higher osmolality than plain milk, emptied more slowly than plain milk in both groups, and this difference was significant in the LM group.
Adult↗
[Lactose--a potential dietary fiber. The regulation of its microecologic effect in the intestinal tract. 4. Dietary fiber action of lactose: evaluation with multivariate statistical analysis].
The conditions and the intestinal processes responsible for the action of lactose as a potential dietary fibre are described. The beta-galactosidase activity in the rat caecum and colon is influenced by dietary factors: It declines with increasing lactose concentration and it rises with increasing protein and phosphate concentration in the diet. The enzyme activity correlates negatively with the content of lactose, and positively with the content of protein and phosphate in the chymus. The products of lactose hydrolysis are degraded by microbial glycolysis in caecum and colon. The glycolytic products are mainly absorbed and energetically utilized by the macroorganism. Phosphate stimulates the microbial metabolism and, therefore, accelerates the consumption of the energy substrate lactose. Mathematical optimization gives the necessary composition of the diet which causes an intended microecological effect. To minimize the chymus pH (5.1 in the colon ascendens; 4.6 in the colon descendens; 4.3 in the faeces) the lactose content of the diet has to be greater than or equal to 160 mumol/g, the protein content less than or equal to 10 mg/g, and the phosphate content less than or equal to 5.5 mumol/g. The minimal pH value depends to a greater extent on variations in the supply of protein and phosphorus with the diet whereas the response to changes in lactose concentration is less noticeable.
Animals↗
Plasmids, loss of lactose metabolism, and appearance of partial and full lactose-fermenting revertants in Streptococcus cremoris B1.
The unstable ability to metabolize lactose (lac) via the phosphoenolpyruvate-phosphotransferase system (PTS) was examined in Streptococcus cremoris B1. The presence of functional lactose-specific PTS enzymes was correlated with the presence of a distinct plasmid species. Characterization of deoxyribonucleic acid extracted from lactose-positive (Lac+) S. cremoris B1 revealed two plasmids having molecular weights of 9 X 10(6) and 36 X 10(6). An acriflavine (BC1)-induced, lactose-negative (Lac-) mutant possessed no plasmids and was devoid of all three lac-specific PTS enzymes. A Lac- mutant (DA2) isolated by growing at elevated temperatures only possessed the 9 X 10(6)-dalton plasmid and also lacked the lac PTS enzymes. A spontaneous Lac- mutant possessed both the 9 X 10(6)-and 36 X 10(6)-dalton plasmids. This mutant displayed FIII-lac and phospho-beta-D-galactosidase (P-beta-gal) activity but was deficient in EII-lac activity. The spontaneous Lac- strain reverted to both full and partial lactose-fermenting phenotypes having FIII-lac, EII-lac, and P-beta-gal activities. BC1 and DA2 Lac- mutants reverted only to the partial lactose-fermenting phenotype having P-beta-gal activity; EII-lac and FIII-lac activities were absent. The results indicate that the genetic determinants for EII-lac, FIII-lac, and P-beta-gal are located on the 36 X 10(6)-dalton plasmid in S. cremoris B1. Evidence for a second chromosomally associated P-beta-gal gene operating in the partial lactose-fermenting revertants is also presented.
DNA, Bacterial↗
Simultaneous assessment of intestinal permeability and lactose tolerance with orally administered raffinose, lactose and L-arabinose.
1. In order to develop an improved differential sugar absorption test for simultaneously assessing intestinal permeability and lactose intolerance, methods were established for determining raffinose, lactose and L-arabinose in human urine. Using NAD(P)H-coupled enzymatic assays and fluorimetry, each sugar was measurable over a concentration range of approximately 3-300 mumol/l in diluted urine specimens. 2. After an overnight fast, 40 normal volunteers drank an iso-osmotic solution containing raffinose, lactose and L-arabinose. The median 5 h urinary sugar excretion was 0.26% of the ingested raffinose, 0.05% of lactose and 17.5% of L-arabinose. 3. In 143 patients with gastrointestinal disease, excretion of both ingested raffinose and lactose was significantly increased in coeliac disease in relapse or in partial remission and in Crohn's disease, but not in the irritable bowel syndrome, coeliac disease in remission or ulcerative colitis. Excretion of lactose, but not raffinose, was increased in patients with mucosal lactase deficiency, whereas excretion of L-arabinose was reduced in all disease groups except ulcerative colitis. 4. Discrimination between diseases was poor when based on individual sugar recoveries, but improved dramatically when excretion was expressed relative to that of L-arabinose. The raffinose/L-arabinose excretion ratio, an index of intestinal permeability, was greater than 0.08 in 15/15 untreated coeliac patients but less than 0.06 in all normal subjects and in 9/9 lactase-deficient patients, 15/16 recovered coeliac patients, 5/6 patients with ulcerative colitis, 13/16 patients with Crohn's disease and 61/62 patients with irritable bowel syndrome.
Adolescent↗