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The slowing of gastric emptying by monosaccharides and disaccharides in test meals.

1. Test meals containing various concentrations of glucose, maltose, sucrose, fructose, lactose, galactose and mixtures of these solutes were given to six healthy subjects. All meals contained 40 mM sodium citrate.2. The slowing of gastric emptying produced by the disaccharides in test meals was generally consistent with the stimulation of duodenal osmoreceptors occuring after the hydrolysis of the disaccharides.3. Glucose was slightly more effective, per osmole, in slowing gastric emptying than was galactose.4. By comparison with glucose or galactose, fructose was much less effective in slowing gastric emptying. In three subjects out of six there was a threshold for its effect.5. The results may be indicative of the relative activities of disaccharidases in the brush border of the small intestine. They are consistent with there being an osmoreceptor deep to these enzymes which slows gastric emptying.

Adult↗

Sequential utilization of mixed monosaccharides by yeasts.

Four yeasts (Saccharomyces cerevisiae, Schizosaccharomyces pombe, Candida utilus, and Rhodotorula toruloides) were tested for their ability to grow and consume D-glucose, D-xylose, D-xylulose, and D-xylitol. Sequential utilization of substrates was observed when D-glucose as mixed with D-xylulose as the carbon source. Catabolite inhibition was tentatively concluded to be responsible for this regulatory mechanism. D-Glucose was also found to inhibit the utilization of D-xylose and D-xylitol in C. utilus and R. toruloides. D-Xylose, D-xylitol, and D-xylulose were consumed simultaneously by R. toruloides and C. utilus.

Ascomycota↗

Extracellular metabolism of sucrose in a submerged culture of Claviceps purpurea: formation of monosaccharides and clavine alkaloids.

Transformation of extracellular sucrose during cultivation of Claviceps purpurea led to the formation of mono- and oligosaccharides. Maltose was a suitable substrate for submerged fermentation of alkaloids. Fermentation in a medium with maltose was characterized by an insignificant formation of glucans, intensive sporulation, suspension growth of mycelium, and a higher formation of elymoclavine. Glucose alone yielded low levels of total alkaloids and high glucan formation; on the other hand, glucose promoted the formation of elymoclavine.

Claviceps↗

Ganglioside and monosaccharide inhibition of nonspecific lymphocyte mitogenicity by group A streptococcal pyrogenic exotoxins.

Group A streptococcal pyrogenic exotoxins (SPE) types A, B, and C are potent nonspecific lymphocyte mitogens. The mitogenicity of these exotoxins was inhibited by gangliosides and sialic acid, whereas concanavalin A was unaffected. The capacity of both concanavalin A and SPE-A to stimulate lymphocytes was suppressed by alpha-methyl-D-mannopyranoside. Galactose reduced the activity of SPE-C. The sugars, glucose, N-acetylglucosamine, alpha-methyl-D-glucopyranoside, and fucose, did not affect SPE mitogenicity.

Exotoxins↗

Inhibition of Pseudomonas aeruginosa adhesion to fibronectin by PA-IL and monosaccharides: involvement of a lectin-like process.

Pseudomonas aeruginosa adherence to fibronectin has been shown to be important to bacterial colonization and infection. To better understand the mechanisms involved in this interaction, the role of the carbohydrate moiety of the fibronectin molecule in P. aeruginosa adhesion was studied. Strain NK 125 502 adhered to immobilized fibronectin with an adherence index of 4.8 x 10(5) CFU/ micro g. Periodic oxidation of fibronectin markedly reduced the adhesion of P. aeruginosa, while a neuraminidase treatment increased bacteria adhesion. N-Acetylgalactosamine, N-acetylglucosamine, sialic acid, and also lectin PA-IL worked as efficient inhibitors in adhesion assays: 59%, 70.7%, 100%, and 60% of inhibition, respectively. We have demonstrated here the involvement of a lectin-like process in the interaction of P. aeruginosa NK 125 502 with immobilized fibronectin.

Acetylgalactosamine↗

Ileal resection and dietary content of sucrose influence the intestinal uptake of monosaccharides.

The intestinal uptake of 0.5 and 40 mM glucose, galactose, and 3-O-methyl glucose (3-O-MG) was examined in vitro in rabbits fed a high (HS) or a low (LS) sucrose diet. In animals with an intact intestinal tract, the jejunal uptake of 0.5 mM 3-O-MG was unaffected by the dietary content of sucrose, whereas the uptake of 40 mM 3-O-MG was lower in LS than HS. The uptake of 40 mM galactose was higher in LS than HS and the uptake of 0.5 mM galactose was similar in HS and LS, whereas the uptake of 0.5 mM but not 40 mM glucose was lower in LS than HS. In animals subjected 6 weeks previously to an ileal resection, the adaptive changes in the jejunal uptake of the hexoses in response to alterations in the dietary content of sucrose differed from the changes observed in rabbits with an intact intestinal tract. For example, feeding HS to ileal resected animals was associated with increased jejunal uptake of 40 mM galactose, decreased uptake of 40 mM glucose, and unchanged uptake of 40 mM 3-O-MG; whereas in control animals with an intact intestinal tract, feeding HS resulted in increased uptake of 40 mM 3-O-MG, decreased uptake of 40 mM galactose, and no change in the uptake of 40 mM glucose. A similar adaptive pattern was noted in the jejunum and ileum for the effect of dietary sucrose on the uptake of 0.5 and 40 mM glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Monosaccharides in health and disease.

In healthy persons, glucose homeostasis maintains blood glucose levels between 70 and 130 mg/dl despite perturbations by meals, fasting, and exercise. Long-term follow-up of diabetic patients has suggested that "good control" of blood sugar levels minimizes the long-term complications of diabetes, such as retinopathy, nephropathy, and atherosclerosis. It now seems likely the products of insulin-independent metabolic pathways in epithelial and endothelial cells leading to polyol formation and protein glycosylation may be factors in the genesis of retinopathy, neuropathy, nephropathy, and premature atherosclerosis of diabetic patients. Dietary complex carbohydrates of various type, including those rich in dietary fiber, which are the cell walls of fruits, vegetables, and cereals, may slow the rate of absorption of glucose from those diets and contribute to a lowering of the postprandial glucose peak. Glycemic responses to various foods compared to glucose have been studied and show a large variation, which is dependent upon gastric emptying, overall effects on rate of hydrolysis and absorption of glucose from food mixtures. Dietary sucrose seems to cause a degree of insulin resistance. The active part of the disaccharide is fructose, which does not elicit an acute insulin response, but appears indirectly to increase insulin levels in both animals and man. Sucrose in animals appears to promote obesity more than glucose because of its lack of stimulation of thermogenesis. Xylitol has been used as a sweetener and as a sugar substitute in total parenteral nutrition. It is a paradox that the most physiological of sugars (glucose) can be a menace at high concentrations. The use of nonphysiological sugars or their derivatives in diabetics and patients with special needs, such as TPN, requires much more investigation to develop a sound rationale in nutrition management.

Animals↗

Ontogenetic development of monosaccharide and amino acid transporters in rabbit intestine.

We measured brush-border uptakes of seven sugars and amino acids by rabbit intestine as a function of age from the day of birth to adulthood. Gut dimensions, especially those of the colon and cecum, increase more rapidly with body weight than would be true if rabbits maintained identical proportions as they grew. However, nominal small intestinal area increases in approximately direct proportion to the animal's basal metabolic rate. For all solutes except fructose, uptake per milligram of intestinal tissue is maximal at or near birth and declines to a level 2.5-5 times lower in the adult. Because of small intestinal growth, though, the total uptake capacity of the whole length of the small intestine increases in approximately direct proportion to metabolic rate. Fructose uptake per milligram is unique in increasing steeply at the time of weaning, correlated with the post-weaning first appearance of fructose in the natural diet. Age-related changes in uptake ratios among aldohexoses or amino acids suggest developmental sequences of related transporters. Correlated with the very high protein content of rabbit milk, the proline-to-glucose uptake ratio is higher in suckling rabbits than in other sucking mammals. Remarkably, the ratio for adult rabbits is higher than in other monogastric herbivores and is instead similar to values for carnivores. In explanation, although the transport capacity of the small intestine appears to account for proline absorption in rabbits of all ages and for sugar absorption in suckling rabbits, the hindgut may be a major site of carbohydrate digestion in adult rabbits.

Aging↗

Intestinal transport of monosaccharides and amino acids during postnatal development of mink.

Intestinal development is typically studied using omnivores. For comparative purposes, we examined an altricial carnivore, the mink (Mustela vison). In mink, intestinal dimensions increase up to 8 wk after birth and then remain constant (length) or decrease (mass) into maturity despite continuing gains in body mass. Rates of glucose and fructose transport decline after birth for intact tissues but increase for brush-border membrane vesicles (BBMV). Rates of absorption for five amino acids that are substrates for the acidic (aspartate), basic (lysine), neutral (leucine and methionine), and imino acid (proline) carriers increase between birth and 24 h for intact tissues before declining, but increase after 2 wk for BBMV. The proportion of BBMV amino acid uptake that is Na(+)-dependent increases during development but for aspartate is nearly 100% at all ages. Tracer uptake by BBMV can be inhibited by 100 mmol/l of unlabeled amino acid, except for lysine. BBMV uptake of the dipeptide glycyl-sarcosine does not differ between ages, is not Na(+) dependent, and is only partially inhibited by 100 mmol/l unlabeled dipeptide. Despite the ability to rapidly and efficiently digest high dietary loads of protein, rates of amino acid and peptide absorption are not markedly higher than those of other mammals.

Aging↗

The kinetics of monosaccharide absorption by human jejunal biopsies: evidence for active and passive processes.

The kinetics of initial rates of uptake of glucose, galactose, arabinose and mannitol have been measured in jejunal biopsies from normal subjects in order to investigate the existence of multiple uptake systems. Glucose kinetics fitted best a model of a saturable uptake system (app Kt = 2.06 +/- 0.33 mM, app Jmax = 93.85 +/- 1.19 nmol/10 min/mg dry weight), together with a linear uptake indistinguishable from the passive uptake of arabinose and mannitol (app Kd = 0.80 +/- 0.05 nmol/10 min/mg dry weight/mM for glucose, 0.75 +/- 0.03 for arabinose, and 0.83 +/- 0.03 for mannitol). The saturable uptake, but not the linear uptake, was inhibited by phlorizin and by the absence of sodium. Cytochalasin B and phloretin had no effect on overall uptake. Galactose kinetics in the absence of inhibitors fitted best a model of a single saturable uptake system (app Kt = 11.05 +/- 0.12, app Jmax = 201.9 +/- 1.13) with no evidence of linear uptake. In the presence of phlorizin, or in the absence of sodium, uptake was predominantly linear with app Kds of 0.84 +/- 0.03 and 0.79 +/- 0.01, not significantly different from the linear component of glucose uptake. We conclude that hexose uptake in human jejunum in vitro occurs by both active and passive routes, and that the active uptake of galactose appears to be inhibited at high galactose concentration.

Adolescent↗

Momordica charantia extracts inhibit uptake of monosaccharide and amino acid across rat everted gut sacs in-vitro.

The inhibitory effects of Momordica charantia extracts were studied on the uptake of glucose and tyrosine across rat everted gut sacs in vitro. The aqueous extract of the plant was found to inhibit primarily the uptake of glucose in a dose-dependent manner. Uptake of tyrosine was affected at high substrate concentrations only. The extract was also found to decrease the absorptive capacity of fluid across the small intestine and sodium ions. It is hypothesized that the effects of Momordica could involve a washout of glucose from the blood stream.

Amino Acids↗