Anton Ailabouni

The contribution of salivary amylase to glucose polymer hydrolysis in premature infants.

ABSTRACT. To determine whether salivary amylase of premature infants can function as a surrogate for pancreatic amylase, we evaluated its production in the infant, acid resistance, and hydrolytic potency in a simulated oropharyngeal, gastric, and intestinal environment. The activity of salivary amylase in 11 prematures varied between 1 and 33 U/ml; the isozymic profile and acid resistance of the premature salivary amylase were identical to those of the enzyme of adults. A “modular” formula containing 7 g/dl of a 14C labeled long chain glucose polymer with degrees of polymerization ranging between 18 and 29 glucose units was prepared. Salivary amylase, 1.1 U/ml, was added to this formula. The progressive breakdown of the 14C polymers as the milk was subjected to oropharyngeal, gastric, and intestinal phase environments was evaluated by quantifying the liberation of short-chain oligomers from the 14C labeled substrates. The gastric pH was varied between 2 and 5 and the gastric incubation time was either 5 or 180 min. Substantial gastric phase breakdown only occurred after 3 h of exposure at the higher pHs of 4 (12%) and 5 (32%). During the intestinal phase, salivary amylase activity resumed. Prior gastric phase pH affected ultimate intestinal phase breakdown, p<0.001; after 5-min gastric phases at pHs ranging from 2 to 5, the intestinal phase breakdown ranged from 17 to 55%. We conclude that the limited salivary amylase in the saliva of premature infants can produce significant glucose polymer digestion in both the stomach and small intestine but the digestion falls substantially short of that accomplished by usual concentrations of pancreatic amylase.

The Jejunal Absorption of Glucose Oligomers in the Absence of Pancreatic Enzymes

Summary: We compared the absorption of carbohydrate from solutions of glucose oligomers and glucose in jejunal Thiry-Vella fistulae, a preparation deprived of pancreatic secretions. The studies were performed with two concentrations (90 and 360 mg/dl) of both glucose and the glucose oligomers. Carbohydrate absorption from glucose solutions (33.1 × 2.8, 115.9 × 8.9 μg/cm/min) was significantly greater (P < 0.025; P < 0.005) than that from oligomer solutions (26.6 × 2.1 and 92.4 × 9.0 μg/cm/min). Thin-layer analyses of the perfusates demonstrate digestion of oligomers with a chain length up to eleven and suggest digestion of oligomers of even greater chain length. Atrophy of the jejunal mucosa occurred over the course of the study as evidenced by a decrease in the ratio of villous height to crypt depth from 3.8 to 0.3, and by a 80% decrease in the activity of maltase, sucrase, and lactase. Atrophy was accompanied by a significant decline in the absorption of both glucose oligomers (P < 0.005) and glucose (P < 0.01) from the more concentrated solutions but the decrement in absorption of both carbohydrates was similar, glucose oligomers, 79.3 × 19.4 μg/cm/min; and glucose, 69.8 × 14 μg/cm/min (P > 0.20). Water absorption was enhanced by both carbohydrates, but there was no demonstrable difference between solutions of glucose and glucose oligomers. The osmolality of the solutions clearly influenced water absorption (P < 0.025) but failed to effect the absorption of carbohydrates.Speculation: In patients with pancreatic insufficiency, solutions of glucose oligomers with low osmolality may provide an adequate source of calories. Although glucose is better absorbed than glucose oligomers from a short segment of jejunum, the length of the small intestine should be adequate to compensate for this difference.~h~ absorption of the glucose oligomers may be a function of polymer length and therefore studies with subfractions separated according to chain length will demonstrate which oligomers are most efficiently absorbed. such information may provide the theoretical hasis for the construction of an ideal carbohydrate supplement for patients with pancreatic insufficiency.

Short-chain fatty acid profile in the colon of newborn piglets using fecal water analysis.

ABSTRACT. Short-chain fatty acid production and assimilation is unlikely to occur at significant levels in the newborn because the colon at birth is sterile, and only gradually acquires an anaerobic flora. This study profiled short-chain fatty acid levels in the colon lumen over the initial 21 days of life. Fecal samples were removed surgically from the cecum, right, and left colon from 36 York piglets, 0-21 days of life. Samples were subjected to in vitro dialysis and centrifugation methods to quantitate fecal water short-chain fatty acids, electrolytes, osmolality, and pH. A three-way analysis of variance examined piglet age, colon site of fecal samples, and method of fecal water analysis, for each variable. No differences were found between techniques of fecal water collection. Newborns showed production of short-chain fatty acids as early as the 1st day of life in limited amounts. Levels were stable between days 5 and 14, and then abruptly accumulated in the lumen. Acetate was predominant early, with propionate and butyrate responsible for late peaks. The production and assimilation of short-chain fatty acids was nearly complete proximal to the left colon. Age and colon site showed significant interactions for each fatty acid (p < 0.001). The combined osmolar contributions of short-chain fatty acids and electrolytes accounted completely for the luminal osmolality after the 2nd wk of life. Previously there was an “osmolar gap” suggesting that lactose or its breakdown products were present in the lumen and were being removed by pathways other than through short-chain fatty acid production.

Galactose-Containing Carbohydrates Are Preferentially Absorbed in the Neonatal Pig Colon

Previous studies on the piglet colon in newborns cleared of bacterial metabolic activity showed a capacity for lactose absorption. Colonic absorption occurred at a flux rate equal to the assimilation of lactose by the small intestine but by a process that did not involve either glucose-galactose sodium cotransport or simple diffusion. Surprisingly, colonic lactose transport did not require either fermentation or cleavage of the disaccharide for uptake. Experiments were designed to test the selectivity of the colonic transport process for a variety of carbohydrates. Colonic tissues from 4-7-d-old piglets were mounted in Ussing chambers and the mucosal-to-serosal flux of radiolabeled carbohydrates was compared with that of lactose. The results showed a 3-4-fold greater flux of galactose-containing sugars as compared with glucose-containing carbohydrates at concentrations up to 40 mM. Even lactulose, a synthetic disaccharide assumed to require bacterial digestion before assimilation, was transported readily.N-Acetylgalactosamine, a component of colonic mucus, inhibited the flux of lactose, whereas N-acetylglucosamine did not. Similarly, lactosylated BSA inhibited lactose flux, whereas nonlactosylated BSA did not. The capacity of the colon of the newborn to differentiate moieties as similar as glucose and galactose suggests an absorptive process for carbohydrates with a high degree of discrimination.

Lactose flux occurs by differing mechanisms in the colon and jejunum of newborn piglets

ABSTRACT: The unidirectional flux of 10− and 40-mM lactose was studied in newborn porcine jejunum and colon mounted in Ussing chambers. Polyethylene glycol 400 was used to measure passive paracellular permeability. The mucosal-to-serosal flux and the tissue accumulation of labeled lactose from the colon was similar to that of lactose-derived glucose from the jejunum. However, only jejunum showed a lactose-stimulated increase in short-circuit current. In jejunum, glucose was the sole sugar identified in the serosal bath, whereas in colon, only intact lactose was identified. Despite colonic lactose flux, polyethylene glycol oligomers were not found in the serosal bath, suggesting that they do not share the same route of absorption. Colonic lactose transport was nonsaturable between 1 and 40 mM. Under nongradient conditions, no net colonic lactose transport was observed. Cumulatively, these data suggest that the colon, unlike the jejunum, does not contain a glucose-galactose sodium cotransporter. The colon of the newborn piglet transports intact lactose at a flux equal to that of lactose-derived glucose by the small intestine, but by a different mechanism that is as yet undefined.

Measurement of the rate of entry of intact colon-derived lactose into the circulation : A model for assessing gut uptake of molecules not endogenously synthesized

BACKGROUND Results of in vitro studies have documented colonic absorption of lactose in the newborn. A stable isotope model was developed for assessing the entry rate of intact lactose into the portal circulation in newborn piglets. METHODS In experiment 1, unlabeled and [D-1-(13C)]-lactose were infused into two separate mesenteric veins, and in experiment 2, labeled lactose was infused into a mesenteric vein and unlabeled lactose was infused into the colon. The 13C-enrichment of plasma lactose was assessed by high performance liquid chromatography gas chromatography combined with mass spectrometry. RESULTS The isotopic estimate of the mesenteric venous infusion rate of lactose was 91% of the theoretical. In the second experiment 13% of the unlabeled lactose infused into the colon reached the portal circulation. CONCLUSIONS The current study provides the first, direct, in vivo confirmation of colon absorption of intact lactose. The tracer model could be used to evaluate intestinal or colonic absorption of other organic compounds not endogenously synthesized, including vitamins or drugs.

Failure to conserve lactose and glucose polymers during frozen storage of fecal specimens: methods for preservation.

Freezing is often used to retard bacterial enzymatic activity in fecal specimens collected to quantify specific carbohydrates. The effectiveness of freezer storage on preservation of lactose and glucose polymers was assessed. The data showed that more than 50% of lactose that was added to fecal supernatants that were stored without treatment for more than 50 days at -20 degrees C was lost. Adjustment of pH with HCl (pH 4.9), with HgCl2 (pH 6.3 or 5.85), or with NaOH (pH 10) improved carbohydrate preservation (P less than 0.0004). Storage of the supernatants of fecal homogenates lessened the loss of carbohydrate compared with the total homogenates (P less than 0.001). In supernatants, degradation occurred via simple hydrolysis; in homogenates, degradation occurred by hydrolysis and fermentation to a variety of end-products. Unprocessed fecal specimens that were frozen for months, then retrieved and incubated with lactose or glucose polymers showed extensive fermentative capacity. Cumulatively, the data indicate that enzymatic activity in feces is not halted by storage in the freezer, even if bacteria have been filtered from the stool.

THE EFFECT OF THE UNSTIRRED WATER LAYER (UWL) ON GLUCOSE OLIGOMER (GO) ASSIMILATION

GOs must pass through the UWL to be digested by brush border glucoamylase which progressively removes glucose units. In the absence of pancreatic amylase (PA), digestion appears rate-limiting for GO absorption. To assess whether the limited diffusivity of long chain GOs affects their assimilation, we evaluated the impact of thinning the UWL on GO uptake in rabbit jejunum proven free of PA. The tissue was mounted in Dietschy chambers, and the thickness of the UWL was adjusted to 140 or 400 um by varying the stirring rate of the mucosal buffer. The uptake of three 14C GOs [glucose (Degree of Polymerization, DP 1), DP 3-8, and DPAVG23] was assessed at cones of 180, 360, and 720 mg/dl.CONCLUSION: The barrier that the UWL presents to the assimilation of GOs is substantially greater for long chain GOs.

680 MIXING CARBOHYDRATES(CHO) - ADDITIVE AND COMPETITIVE EFFECTS ON ABSORPTION

When intestinal absorptive function is limited, it may be possible to enhance CHO absorption by combining CHOs having different digestive-absorptive pathways. Employing single pass perfusion studies in partially atrophic amylase-free canine jejunal Thiry-Vella fistulae we found that absorption of glucose(G), sucrose(S), and long chain glucose polymers (LCGP) was saturable with infusion conc. of 882, 378, and 347 mg/dl respectively. Absorption of S and LCGP was additive even from solutions containing 900 mg/dl of each sugar (S=159±16, LCGP=70±6, mixture=235±22 μgms/cm/min.). Virtually no G was found in the fistula effluents (<0.1 mg/ml). Adding 900 mg S to 900 mg LCGO did not improve CHO absorption beyond values for 900 mg/dl of G infused alone (378±16 μgms/cm/min.). Addition of the Vmax conc. (400 mg/dl) of LCGP to the Vmax conc. of G (900 mg/dl) causes mutual inhibition of the absorption of both (G, 346±23 vs. 232±25; LCGP, 63±8 vs. 28; p<.001). Additive absorption occurs with addition of 400 mg/dl LCGP to 500 mg/dl of G (LCGP=56±8, G=152±8, mixture=208±10).Conclusions: 1)For G polymers and S, hydrolysis, not absorption of the resultant monosaccharides, is rate limiting for jejunal assimilation. 2)G and LCGP either interact in the glycocalyx or compete for absorptive pathways. 3)S does not compete with LCGP for absorption.Speculation: In formulating enteral feedings or rehydration solutions mixtures of S and LCGP may enhance absorption, but addition of LCGP to G may be deleterious.

COLON SHORT CHAIN FATTY ACID (SCFA) PROFILE IN THE NEWBORN

Carbohydrates are fermented by anaerobic colon flora to gas (CO2, H2, CH4) and SCFA (acetate, propionate, and butyrate) in human adults. SCFA absorption is critical to normal colon function. Human neonates rely on colon bacteria to retrieve over 50% of lactose (LAC) calories. Yet SCFA pathways are unlikely to be significant in neonates since the colon at birth is sterile and only gradually acquires an anaerobic flora. Kecal SCFA levels were profiled over the initial 21 days of life.Methods: York piglets, n=38, 0-21 day, had feces removed surgically from cecum, right and left colon sites. Samples (n=111) were centrituged and supernate analyzed for electrolytes (EL:sodium, potassium, bicarbonate and chloride), SCFA, osmolality, and pH.Results: Newborns showed early production of SCFA (mmoles/kg stool). Levels stablized between days 5 and 14, with an abrupt accumulation in the cecum following day 14. Acetate predominated early, with propionate and butyrate responsible for later peak levels in total SCFA. Production and assimilation of SCFA is nearly complete proximal to the left colon. By two-way analysis of variance, age and colon site are significant factors, p < .001. The combined osmolar contributions of EL and SCFA account completely for luminal mOsm after day 16. Prior, there is an “osmolar gap”, suggesting that LAC or its fermentation products are present in the lumen and are removed by pathways other than SCFA.