Pierre Vaugelade

Splanchnic fluxes of amino acids after duodenal infusion of carbohydrate solutions containing free amino acids or oligopeptides in the non-anaesthetized pig

Seven non-anaesthetized pigs (mean body-weight 64.6 kg) were used to study the intestinal absorption and hepatic metabolism of glucose and amino acids (AA) using carbohydrate solutions (maltose dextrin; 440 g/2 I), containing 110 g of either an enzymic milk-protein hydrolysate (PEP) with a large percentage of small peptides (about 50% with less than five AA residues) and very few free AA (8%) or a mixture of free AA (AAL) with an identical pattern, infused intraduodenally. Each pig was previously fitted under anaesthesia with electromagnetic flow probes around the portal vein and the hepatic artery, and with permanent catheters in the portal vein, carotid artery, one hepatic vein and the duodenum. Each solution was infused for 1 h after a fasting period (18 h) and each pig received both solutions at 8 d intervals. The observation period lasted 8 h. For most AA (his, lys, phe, thr, arg, tyr, pro) the absorption rate after infusion of PEP was significantly higher than after that of AAL during the 1st hour, but the differences quickly disappeared. After 8 h, the only differences concerned his and tyr (PEP > AAL) and met, glu and asp (AAL > PEP). There was a large uptake of blood AA by gut-wall cells, higher after AAL infusion than after PEP infusion, particularly for branched-chain AA (BCAA). The absorption of ammonia-nitrogen after both infusions was equivalent to two-thirds of urea-N passing from blood to intestinal tissues and lumen. Glucose absorbed within 8 h represented only 76% (PEP) or 69% (AAL) of the infused amounts. The cumulative hepatic total AA (TAA) uptake increased from 13 to 27% of the infused amounts between the 1st and the 8th hour after PEP infusion, and from 8 to 31% after AAL infusion. Most essential AA were largely taken up by the liver, with the exception of met (PEP) and thr and of BCAA, which were poorly retained for both solutions; there was a high uptake of ala and gly, and a release of asp, glu, and gln. Urea-N released by the liver within 8 h was equivalent to 23-25% absorbed amino-N and to around 1.5 times ammonia-N taken up by the liver within 8 h. Glucose was highly taken up by the liver during the first hours then released, the total uptake within 8 h representing about half the absorbed amount.(ABSTRACT TRUNCATED AT 400 WORDS)

Intestinal absorption and liver uptake of medium-chain fatty acids in non-anaesthetized pigs

In order to study the rate of intestinal absorption and hepatic uptake of medium-chain fatty acids (MCFA), six growing pigs, mean body weight 65 kg, were fitted with a permanent fistula in the duodenum and with three catheters in the portal vein, carotid artery and hepatic vein respectively. Two electromagnetic flow probes were also set up, one around the portal vein and one around the hepatic artery. A mixture of octanoic and decanoic acids, esterified as medium-chain triacylglycerols, together with maltose dextrine and a nitrogenous fraction was continuously infused for 1 h into the duodenum. Samples of blood were withdrawn from the three vessels at regular intervals for 12 h and further analysed for their non-esterified octanoic and decanoic acid contents. The concentration of non-esterified octanoic and decanoic acids in the portal blood rose sharply after the beginning of each infusion and showed a biphasic time-course with two maximum values, one after 15 min and a later one between 75 and 90 min. Only 65% of octanoic acid infused into the duodenum and 54% of decanoic acid were recovered in the portal flow throughout each experiment. The amounts of non-esterified MCFA taken up per h by the liver were close to those absorbed from the gut via the portal vein within the same periods of time, showing that the liver is the main site of utilization of MCFA in pigs. These results have been discussed with a special emphasis laid on the possible mechanisms of the biphasic time-course of MCFA absorption and the incomplete recovery in the portal blood of the infused fatty acids.

Absorption kinetics of some carbohydrates in conscious pigs: 1. Qualitative aspects

Concentrations of reducing sugars, glucose, fructose and lactic acid in blood obtained from arterial and portal catheters were measured for periods of 8-24 h in twenty-three unanaesthetized pigs (mean body-weight 50 kg). From 6 to 8 d after implantation of catheters, the animals received experimental meals containing different levels (400, 800, 1200, 1600 g respectively) of different sugars (glucose ten meals, sucrose eighteen meals, lactose nine meals, maize starch sixteen meals) as well as a protein-mineral-vitamin premix. After each meal the reducing sugars appeared in the portal blood in successive waves. The porto-arterial differences in the concentration of reducing sugars, representing the real appearance of sugar-hydrolysis products in the animal, varied greatly according to the sugar ingested and its level of intake. For each level of intake, these differences were larger, but of shorter duration, for glucose and sucrose than for maize starch. For these three carbohydrates, the higher the level of ingestion, the larger and the more persistent the porto-arterial differences. Lactose represented a special case, as the porto-arterial differences of reducing sugars were always much lower than those obtained with the other sugars and they did not vary with the level of intake. Our findings show that the products formed by feeding glucose and sucrose appear more rapidly in the portal blood than those formed by feeding lactose. Accordingly, the length of time of digestion of glucose and sucrose is shorter than that of maize starch and lactose.

Intestinal Oxygen Uptake and Glucose Metabolism During Nutrient Absorption in the Pig

Abstract Intestinal transport of nutrients coincides with their partial catabolism in the gut. The aim of the present study was to measure intestinal oxygen consumption and nutrient metabolism after a meal or during a short fast. Nutrient and oxygen balances across the small intestine were measured in consclous 50 kg (live wt) pigs. Jejunal enterocytes were also isolated from 1-hr postprandial, postabsorptive, or 3-day fasted pigs, in order to evaluate their capacities to metabolize 5 mM glucose and 2 mM glutamine. Whatever the nutritional state, intestinal oxygen consumption was high, since 26 ± 2% (n = 6) of the oxygen arterial supply was extracted by the small intestine. Furthermore, the consumption of a mixed meal induced a rapid and transient rise in oxygen consumption. In the postabsorptive state, the intestinal uptake of glucose (0.31 ± 0.08 mmole/min, n = 6) was twice higher than that of glutamine. The role of glucose as a fuel was also evidenced after a 3-day fast. During nutrient absorption, glutamine was highly utilized, and lactate was produced. The capacity of enterocytes isolated from fed pigs to metabolize glucose was dramatically reduced, as was 6-phosphofructo 1-kinase activity. In contrast, intestinal muscle presented a high glycolytic capacity from glucose, suggesting that the main site of intestinal lactate production during nutrient absorption would be the muscular rather than the epithelial layer.

Supplementation of pig diet with algal fibre changes the chemical and physicochemical characteristics of digesta.

Seaweed extracts, because of their physicochemical characteristics and potential nutritional value, could provide a new source of dietary fibre. This study investigated changes in seaweed fibres (physicochemical and fermentative properties) in different digestive sites and their effects on digesta (viscosity and hydration properties). Sixteen pigs were adapted to a test diet supplemented with 5% algal fibre (either Palmaria palmata (PP), a poorly viscous soluble xylan; or Eucheuma cottonii (EC), a partly insoluble carrageenan; or Laminaria digitata (LD), a highly viscous soluble alginate) or 5% cellulose (reference fibre). PP did not modify the characteristics of digesta and was fermented in the caecum (pH 6.1 ± 0.4; short-chain fatty acids measured in digesta, 1409 ± 691 µmol g−1 dry matter). EC and LD were mainly insoluble in the stomach, becoming soluble in the intestine; EC was slightly fermented in the colon, giving a low concentration of short-chain fatty acids (303 ± 122 µmol g−1 dry matter). Supplementation of the diet with alginate (LD) increased 3.5-fold the ileal viscosity of digesta and their hydration capacity in the ileum and colon. Thus the physicochemical properties of pig digesta largely depend on the physicochemical properties of the ingested seaweed fibre, the pH and ionic conditions prevailing in the gut, and their fermentability. © 2000 Society of Chemical Industry

Portal hyperglutamatemia after dietary supplementation with monosodium glutamate in pigs.

The aim of the present work was to examine in pigs the effect of a dietary supplementation with the flavor enhancer monosodium glutamate (MSG) on intestinal amino acid metabolism. For this purpose, pigs weighing 60 ± 2 kg received a standard meal twice a day for 1 week, supplemented with either 10 g MSG per meal or, as control experiments, an isonitrogenous amount of glycine together with an equal amount of sodium in the form of NaCl, the animals being their own control in all experiments. At the end of this period, pigs received a MSG or glycine-NaCl-supplemented meal and samples of portal and arterial blood were collected for amino acid analysis in plasma. The results demonstrate after MSG supplementation rapid significant increases in glutamate concentration in the portal and arterial blood plasma after a test meal which resulted in a positive portoarterial difference. In comparison, after glycine-NaCl supplementation, glutamate concentrations were almost identical in portal and arterial plasma. Furthermore, significant increased aspartate concentration in the portal blood plasma was observed after MSG supplementation when compared with control experiments. When enterocytes were isolated at the end of the supplementation period from the jejunum and examined for their metabolic capacities towards L-glutamate and L-glutamine, it was found that metabolism did not differ according to the supplement used, with glutamate and glutamine being oxidized and transaminated at a similar level. It is concluded that the portal hyperglutamatemia observed shortly after the ingestion of a MSG- supplemented meal is likely due to the saturation of the intestinal capacity to metabolize glutamate with no measurable adaptation of the metabolic pathways controlling glutamate metabolism in enterocytes.

Changes Induced in Colonocytes by Extensive Intestinal Resection in Rats

After massive intestinal resection, physiological compensatory events occur in the remnant small bowel and in the colon. The aim of our work was to study the propensity of the colon to evolve after a massive small bowel resection in rats. The resected group, where 80% of the small bowel length was removed, was compared with sham-operated rats (transected). During the 7 postoperative days, rats were fed orally or they received an elemental nutrition through a gastric catheter. PepT1 and NHE3 mRNAs encoding apical membrane transporters were not modified in the present experiment. However, two unexpected genes (I-FABP and UroR) were up-regulated in the colon following intestinal resection. These modifications occurred without an imbalance of cell cycle protein content and in a context of low short-chain fatty acid production.

Luminal fermentation and colonocyte metabolism in a rat model of enteral nutrition.

Large intestinal fermentation and nutrient metabolism in colonocytes were investigated in a rat model of enteral feeding. Male Wistar rats (240–280 g) were submitted to 7 or 14 days of treatment: intragastric feeding (elemental formula) versus oral feeding (isocaloric and isonitrogenous diet, containing 5% purified cellulose) in the control group. Fermentation products and bacterial populations were analyzed in cecal contents. Colonic cells were isolated and tested for their capacities to metabolize [1-14C] butyrate and [U-14C]glutamine. After 7 days of enteral nutrition, short-chain fatty acid concentrations represented 52% of those measured in the control group, but colonocyte metabolism remained unchanged. After 14 days of enteral nutrition, short-chain fatty acid concentrations were still decreasing, although bacterial counts remained unchanged. In parallel, ammonia and lactate concentrations were significantly increased. The capacities to utilize butyrate and glutamine in colonocytes were only slightly affected. However, there was a dramatic increase in the ratio of β-OH-butyrate to acetoacetate fluxes, suggesting a more reduced redox mitochondrial state associated with enteral feeding.

Quantitative Measurement of Endogenous Amino Acid Absorption in Unanaesthetized Pigs

The present experiment was carried out with 11 pigs (mean body weight: 53.9 +/- 1.3 kg) fitted with permanent catheters in the portal vein and carotid artery and with an electromagnetic flow probe around the portal vein. They were each subjected to 2 or 3 trials at 3 to 4-day intervals. During each trial the animals received after a previous fasting of 20 h a given amount of a protein-free diet (200 to 1200 g). The blood was collected either continuously for a quantitative determination of amino nitrogen, reducing sugars, urea and ammonia (number of meals 12, mean intake: 727 +/- 60 g) or discontinuously every 30 min between 0 and 8 h after the meal for amino acid analysis (number of meals 8; mean intake 709 +/- 105 g). A rather constant appearance (2 g/h) of amino acids in the portal blood was observed throughout the postprandial period. The intestinal absorption of each amino acid was however variable and represented between 10 and 50% of the daily requirements of the animal during the measuring period (8 h). Glutamine and to a less extent glutamic acid were exceptions as they were taken up by the gut wall from the arterial blood. There was also a marked synthesis of ornithine and citrulline by the latter. Because of the low blood level of urea, there were no apparent exchanges of urea between the blood and the intestine; in contrast, the ammonia absorption represented about 70% of that observed after ingestion of normal protein diets. Most amino acids are largely taken up by the liver and peripheral tissues, but in the case of alanine the syntheses exceed the uptake.

Kinetics and Balance of Glucose and Galactose Appearance in the Portal Blood after Intake of Lactose or Hydrolysed Lactose in Conscious Pigs

Five pigs (mean body weight: 66.2 kg) were fitted with portal and arterial catheters and an electromagnetic flow probe around the portal vein. One week after the surgical operation, each animal was successively fed, at 3-day intervals, with two experimental meals containing 392 g dry matter either from hydrolysed or non-hydrolysed lactose together with a protein-mineral-vitamin mixture (200 g). Portal and arterial blood concentrations of glucose, galactose and amino nitrogen were measured together with the portal blood flow rate during a postprandial period of 8 h after the intake of these experimental meals. Amounts of hexoses appearing in the portal blood after hydrolysed-lactose intake were 3- and 2-fold larger within 2 and 8 h, respectively, than after non-hydrolysed-lactose intake. Thus, enzymatic hydrolysis in the intestine is the limiting factor of lactose digestion in unadapted pigs. Whatever the type of lactose ingested, glucose appeared more rapidly and in larger amounts in the portal blood than galactose. After hydrolysed-lactose intake, the amount of glucose appearing in the portal blood exceeded the amount ingested already after 5 h. This means that a fraction of galactose was transformed into glucose during the transport by the enterocyte.