Stable isotope model for assessing production of short chain fatty acids from colon-derived sugar: application in pigs

Sugar reaching the colon because of intestinal maldigestion or malabsorption may be fermented to acetate and other short-chain fatty acids, resulting in stimulation of colonic water absorption and cell proliferation. To explore this phenomenon in more detail, we have developed a stable isotope model for estimating the fraction of colon-derived glucose or lactose that is fermented to acetate, propionate and butyrate. In an initial application of the model, [d3]-acetate and either [1-(13)C]-glucose or [D-1-(13)C]-lactose were infused into the cecum or colon of piglets, and plateau plasma acetate enrichment was monitored in the carotid artery. In acutely anesthetized piglets, the fractions of glucose and lactose fermented to acetate were 17.0 and 20.0%, respectively. In a chronically catheterized piglet, fermentation was higher (34.2%). When conducted in chronically catheterized animals or via a colostomy or ileostomy in infants, this model may be used to determine how age, previous surgery or antibiotic therapy affects the efficiency of colonic assimilation of carbohydrate.

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.

Absorption of theophylline from the small and large intestine of the neonatal piglet

In this study, the newborn piglet model was used to assess theophylline absorption from various areas of the GI tract. 13 piglets, ages 9-14 days, had their intestines surgically exposed. Four segments of equal length (jejunum, ileum, right colon and left colon) were simultaneously perfused with a saline solution containing [3H]-polyethylene glycol 4000 to measure water shifts and theophylline at a total dose of 5 mg/kg, a typical neonatal dose. Absorption of theophylline, appearance in serum, and the effects of the drug on water and electrolyte movement in the intestinal segments were monitored. Serum concentrations of theophylline after an intravenous and oral dose were also studied in 2 piglets. The data showed excellent absorption of the drug from all intestinal segments studied (jejunum 0.97 +/- 0.16, ileum 0.7 +/- 0.13, right colon 0.7 +/- 0.13, and left colon 0.88 +/- 0.19 micrograms/cm/min), despite a concomitant secretion of sodium chloride and water. No statistical differences in absorptive capacity were seen among segments. The results suggest that as little as 100 cm of residual intestine could, theoretically, absorb a 5 mg dose of theophylline if presented slowly. These findings have ramifications for neonates who may receive theophylline orally or rectally.

Absorption of valproic acid from the gastrointestinal tract of the piglet

Valproic acid is a commonly used drug for the treatment of epilepsy. Since valproic acid can only be given orally, its absorption from the gastrointestinal (GI) tract especially in patients with short bowel syndrome (SBS) and in neonates is important. The specific sites of absorption for valproic acid in the small intestine and colon have not been investigated. It is currently unknown whether these patients are able to absorb oral valproic acid sufficiently to maintain a therapeutic serum concentration. The primary objectives of the study were to: (a) determine the relative absorption of valproic acid from specific sites in the GI tract; and (b) investigate the influence of intestinal development on valproic acid absorption using the newborn piglet as a model. Two groups were studied: Group I included 5 piglets 18-21 days of age, and Group II included 5 piglets 1-3 days of age. A valproic acid solution was simultaneously perfused through 5 partitioned segments of the gastrointestinal tract: the duodenum, jejunum, ileum, right colon and left colon. Tritiated [3H] polyethylene glycol was co-administered to monitor water movement across the GI mucosa. Following steady state, samples were collected from each segment, and analyzed by a specific enzyme-mediated immunoassay. The absorption rates (micrograms/min/cm) of valproic acid in Group I were as follows: 9.96 +/- 2.8 duodenum; 11.28 +/- 2.79, jejunum; 9.42 +/- 3.34, ileum; 10.88 +/- 3.35, right colon; 10.96 +/- 2.92, left colon.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of stable isotopic enrichment of underivatized acetate by gas chromatography/mass spectrometry: application to in vivo estimation of acetate production

In order to assess endogenous and colonic production of acetate, we have developed an assay for determining the isotopic enrichment of plasma acetate using gas chromatography/mass spectrometry (GC/MS). Acidified, deproteinized plasma (200 microliters) was extracted into ethyl ether, and the ether phase was then injected into a gas chromatograph/mass spectrometer fitted with a 30 m x 0.252 mm i.d. capillary column (temperature program 50-245 degrees C at 10 degrees C min-1). Using electron impact GC/MS and selected ion monitoring, peak areas of ions with m/z 60 and 61 (M + 1) were determined. Triplicate extractions of enriched plasma samples (mol.% excess 1.38-1.5%) resulted in a coefficient of variation of 1.6-5.9%. Unenriched plasma samples were found to have an enrichment close to theoretical natural abundance, and analysis of our (1-13C)acetate tracer (99 at.% excess) revealed an ion at m/z 61 and no ion at m/z 60. To verify accuracy, we conducted an in vivo isotope dilution study. In a 1-month-old piglet, fasted for 24 h, changing the rate of a 4 h infusion (mmol h-1) of (1-13C)acetate from 0.141 to 0.282 doubled the isotope enrichment (2.08 x) of the second plateau. The rate of appearance of acetate was 26.0 mumols kg-1 min-1, which is comparable to that reported in fasting sheep.

Stimulatory effects of short-chain fatty acids on colonic absorption in newborn piglets in vivo

This study examined the absorption of short-chain fatty acids (SCFA) and their effects on colonic conservation of water and sodium. Newborn York piglets, 2-23 days of age and exclusively suckled, were studied comparing absorption from a control/electrolyte solution with that from a SCFA solution. The results indicated that SCFA absorption is highest at birth, with a rapid decline over 72 h to a lower and relatively stable level. During the control perfusions, water and sodium absorption increased with age. The addition of SCFA to the perfusate stimulated both water and sodium uptake in the first 2 weeks. After the 14th day, sodium absorption continued to be enhanced by SCFA, but water movement remained unchanged from control levels. Right and left colon responses were similar. The results suggest that although luminal SCFA levels may be limited early in life, the presence of SCFA has stimulatory effects on the absorption of sodium and water from the colon in newborns.

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

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 less than 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.

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

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 less than 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.

Large scale production of glucose oligomers and polymers for physiological studies in humans

Methods for isolating relatively large quantities of glucose oligomer and polymer subfractions from a partial corn starch hydrolysate (PCSH) are described. To ensure that the products are suitable for physiological studies in humans, potentially toxic substances were excluded from the preparative processes. For long chain glucose polymer fractions with degrees of polymerization (DP) averaging 43 glucose units, we employed molecular filtration through Amicon YM5 membranes. For fractions containing glucose oligomers with DP's 3 through 8, we employed yeast fermentation followed by ethanol fractionation.