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The contribution of the research group set up by Rérat in the early 1960s in Jouy-en-Josas, and then expanded to Rennes, is summarised. As digestive processes are a major key to the nutritional status of monogastric animals, original methodologies based on advanced experimental surgery were developed in the pig to quantify the digestion and absorption yield, to know their factors of variation, and to understand their physiological and nutritional consequences. The group also extended its expertise to the control of food intake, the role of the nervous system and regulatory peptides, and several biomedical gut-related topics.

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The purpose of this study with the pig was to analyse the influence of the type of dietary fibre on quantitative kinetics of the absorption of nutrients deriving from enzymatic digestion in the small intestine and that of volatile fatty acids (VFA) deriving from microbial digestion in the hindgut influenced by the length of adaptation to the diet. Two groups of four pigs were fitted with a device for measuring absorption by simultaneous analysis of the differences in the porto-arterial concentrations of nutrients and metabolites and of the portal blood flow rate. They received successively two diets containing fish- and heat-treated potato flour, balanced in vitamins and minerals, and only differing in the type of fibre added at the inclusion level of 10%: wheat bran (S) or sugar beet fibre (P). Following an adaptation period of 30 d (C) or 5 d (A) to each of these diets, and after the last experimental meal of 800 g, the animals were subjected for 12 h to blood samplings every 30-60 min for the analysis of glucose, amino-nitrogen and volatile fatty acids (VFA) with a simultaneous recording of the portal blood flow-rate. The type of dietary fibre did not modify nutrient absorption (glucose and amino-nitrogen) but affected the amounts of VFA appearing in the portal blood. These amounts were higher (P < 0.001) after ingestion of the sugar beet fibre-rich diet (group PC + PA: 766 mmol/12 h) than after that of the wheat bran-rich diet (group SC + SA: 477 mmol/12 h). The proportion of acetic acid in the absorbed mixture rose (PC + PA 63.6% versus SC + SA 58.5%, P < 0.01) at the expense of propionic acid (PC + PA 27.4% versus SC + SA 31.0%, P < 0.01). Prolongation of the adaptation period from 5 to 30 d led to a decrease in the absorption of nutrients deriving from enzymatic digestion in the small intestine (glucose g/12 h: SA + PA 341.8 versus SC + PC 244.5, P < 0.01; amino-nitrogen g/12 h: SA + PA 29.4 versus SC + PC 21.0, P < 0.001) without any subsequent change in the absorption of the volatile fatty acids.

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Recent papers about bovine spongiform encephalopathy (BSE) and new variant of Creutzfeldt-Jakob disease (nvCJD) are reviewed: new data, maternal transmission of BSE, epidemiology of BSE in British cattle, structure of the PrP(res), biochemical signature of PrP(res), chronic pesticide-initiated modification of the prion protein, protein markers in cerebrospinal fluid.

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A simple simulation model of digestion and absorption in pigs was developed. The structure of the model is a set of four anatomical compartments for DM: stomach, two portions of small intestine, and the large intestine. In each of these anatomical compartments, subcompartments correspond to the major biochemical components of feed and their products of degradation. The major degradation and absorption events are considered as well as the effect of microbial activity in the large intestine. The total number of compartments is 44. The numerical integration with a time step of 1 min allows prediction of kinetic features of digestion phenomena such as absorption patterns and transit flows. First validation of the model shows that the global dynamic behavior of the model is realistic and promising. However, some additional factors must be considered for improved accuracy, in particular the susceptibility of the feed components to enzymatic degradation. The outputs of such a model could be used as inputs for metabolic or growth models running with time steps smaller than the 24-h basis often used in nutrition.

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The observation in 1995 and 1996 of 12 cases of a new variant of Creutzfeldt-Jakob disease (V-CJD) in U.K. suggested a possible relation between this human cases and bovine spongiform encephalopathy (BSE). Recent papers about this topic are reviewed: BSE transmission to macaques, transmission of scrapie with embryo transfer, incidence of maternal transmission, PrP protein released by platelets, diagnostic test by detection of PrP protein in tissues of sheep, epidemiology of BSE, french regulations, identification of cattle in U.K.

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The observation in 1995 and 1996 of 10 cases of a new variant of Creutzfeldt-Jakob disease (V-CJD) in U.K. suggested a possible relation between this human cases and bovine spongiform encephalopathy (BSE). Recent papers about this topic are reviewed : hypothesis of a possible genetic link between man and cattle, hypothesis of a acquired resistance against the agent of BSE after a previous infection by a less virulent agent of ovine origin, importance of polymorphism at codon 129 according to the hypothesis of a virus-induced amyloidosis, diagnostic test with cerebrospinal fluid, epidemiology of BSE and prediction of future BSE spread.

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An experiment was conducted in the pig to determine the consequences of deprivation of exocrine pancreatic secretion on the composition and quantity of nutrients absorbed after intake of a balanced diet. Five growing pigs (53.8 kg body weight) were fitted with permanent catheters in the portal vein and the carotid artery and with an electromagnetic flow probe around the portal vein to measure the exchanges between the blood and the intestinal lumen. They were also fitted with a permanent catheter in the duct of Wirsung to educe the exocrine pancreatic secretion and another one in the duodenum in order to reintroduce it. In each animal, glucose, amino-N and amino acid absorption as well as insulin and glucagon production were measured over a period of 10 h after the meal (semi-purified diet based on purified starch and containing 180 g fish meal/kg, DM content of the meal 731 g), either in the presence of pancreatic juice (group C: immediate reintroduction), or in the absence of pancreatic juice (group D: deprivation). The deprivation of pancreatic juice provoked a marked depression in the absorption of glucose (D 67.9 (SEM 27.9) g/10 h, C 437.7 (SEM 39.5) g/10 h, P < 0.001), and of amino-N (D 7.55 (SEM 0.54) g/10 h, C 15.80 (SEM 0.79) g/10 h, P < 0.001). The composition of the mixture of amino acids in the portal blood was only slightly modified: only the levels of histidine (P < 0.05) and of valine (P < 0.06, NS) decreased in the absence of pancreatic juice. Insulin production was much lower (by 64%, P < 0.05) in the absence of pancreatic juice whereas that of glucagon was not affected.

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The results of three successive experiments were compared in order to analyse the chronology of absorbed energy amounts resulting from enzymatic or microbial digestion, respectively. These experiments were undertaken in the pig to study the absorption kinetics of reducing sugars and amino-nitrogen formed during enzymatic digestion and of volatile fatty acids (VFA) formed through the action of the digestive flora. The animals were given well-balanced semi-synthetic diets containing poorly digestible or indigestible carbohydrates. These diets contained the following ingredients: (Experiment A) purified cellulose at two levels of incorporation (LC diet 6%, HC diet 16%); (Experiment B) alfalfa meal (22%) supplying 6% crude fibre (HA diet) versus lactose (22%) with an addition of 6% purified cellulose (HL diet); (Experiment C) sorbitol in the form of maltitol (53%) with an addition of 6% purified cellulose (SHyd diet) versus maltose under the same conditions (53%, SNat diet). Each diet was fed to five pigs fitted with catheters placed in the portal vein and carotid artery and with a flow probe around the portal vein, which made it possible to study the nutrient absorption after one meal (800 g). Under our experimental conditions (intake: 2 200-2 300 kcal, except HC 1 930 kcal) the higher level of crude fibre or the presence of osides in the diet which are poorly digestible in the small intestine (lactose, maltitol), depressed the absorption of reducing sugars (RS) (amount absorbed within 12 h relative to intake %: SNat 92.8; LC 82.7; HL 78.7; HA 76.0; HC 72.5; SHyd 71.3). The absorbed energy supply resulting from the VFA increased accordingly, in the presence of poorly digestible or indigestible carbohydrates (as a percentage of the total energy absorbed as RS, lactic acid (LA) and VFA: SNat 3.4; LC 7.1; HL 8.9; HC 10.4; SHyd 13.1) with one exception (HA: 6.0%). For all diets, the greatest energy absorption (42-63% according to the diet) occurred during the first 4 h after the meal, the larger fraction resulting from RS (86.8-94.8% according to the diet). The energy supply due to the absorption of VFA became large between the 5th and the 12th hour, and was larger for diets containing poorly digestible or indigestible carbohydrates (as a percentage of the total RS + LA + VFA: SNat 6.5; LC 8.7; HC 14.3; HC 14.4; SHyd 23.3) with one exception (HA: 9.0%). Although the late absorption of VFA was insufficient to compensate for the energy deficit due to a lower of RS, it may bridge the energy gap during the interprandial period.

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When pigs were submitted to duodenal infusion of solutions containing a large percentage of small peptides (PEP) or free amino acids with the same pattern (AAL) amino acids appear in the portal blood more rapidly and more uniformly after infusion of PEP then after infusion of AAL, with the notable exception of methionine for which the opposite was true. These differences were lowered when a carbohydrate (maltose dextrin) was present in the solution, but nevertheless remained significant for the first hour after the infusion. The long-term (8-hour) uptake of free amino acids into the liver and the peripheral tissues differed in profile according to the nature of the duodenal infusion. Peripheral uptake was appreciably less well balanced after infusion of free amino acids (deficiency of threonine and phenylalanine) than after infusion of small peptides (deficiency of methionine). Accordingly, in the rat, under conditions of discontinuous enteral nutrition the mixture of small peptides was of greater nutritive value than the mixture of free amino acids. It thus appears that the absorption kinetics which results in important variations in the temporal distribution of free amino acids in the tissues may be at the origin of transitory imbalances in tissue amino acid uptake, and as a result of a lower nutritive value.

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In order to study the influence of pancreatic enzyme secretion on the intestinal absorption of medium-chain fatty acids (MCFA), three growing pigs (mean body-weight 61 kg) with ligated and severed pancreatic ducts were fitted with a permanent fistula in the duodenum and with two catheters in the portal vein and carotid artery respectively. An electromagnetic flow probe was also set up around the portal vein. A mixture of octanoic and decanoic acids, esterified as medium-chain triacylglycerols, together with maltose dextrine and nitrogenous fraction was continuously infused for 1 h into the duodenum. Samples of blood were withdrawn from the two vessels at regular intervals of time for 8 h and further analysed for their non-esterified octanoic and decanoic acid contents. The concentrations of non-esterified octanoic and decanoic acid in the portal blood increased slowly after the beginning of each infusion, reaching about 10 times higher values than the basal level. Only 26% of octanoic acid infused in the duodenum and 27% of decanoic acid were recovered in the portal flow throughout each experiment. The possible mechanisms underlying the appearance of MCFA in the portal blood in the absence of pancreatic enzyme secretions and the importance of duodenal absorption of MCT in such physiological conditions have been discussed.

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Because sorbitol is poorly absorbed in the small intestine, it may be the origin of large amounts of residues reaching the large intestine and may be substrate for microbial activity. An experiment was conducted to study the quantitative appearance in the portal blood of nutrients and metabolites derived from enzymatic hydrolysis and microbial fermentation in the fore- and hindgut. Five Large White, castrated male pigs (mean BW of 61.2 +/- 1.7 kg) were fitted under anesthesia with an electromagnetic flow probe around the portal vein and with permanent cannulas in the portal vein and the carotid artery. From 10 d before surgery, they were accustomed to one of the two semisynthetic, well-balanced diets, containing a high level (53% of DM) of either a maltose-rich glucose syrup (SNat) or of a maltitol-rich hydrogenated glucose syrup (SHyd). Eight days after surgery and after an 18-h fast, each animal was given a last meal (800 g) of the diet to which it was formerly accustomed. For 12 h after this meal, blood samples were taken at 30- to 60-min intervals for glucose, sorbitol, amino N, VFA, D- and L-lactic acids, insulin, and glucagon determinations, and portal blood flow was continuously recorded. The absorption coefficients (amounts appearing for 12 h in the portal blood: amounts ingested, percentage) of glucose and of amino N were not significantly different between the two diets. The amount of sorbitol that appeared within 12 h in the portal blood after SHyd intake was 44 g (25% intake). The amount of VFA that appeared in the portal blood within 12 h was 2.7 times larger (P < .05) after intake of the maltitol-rich diet (SHyd:808 mmol) than after intake of the maltose-rich diet (300 mmol). This difference was due to an increase in absorbed amounts of propionate (SHyd 402 vs SNat 56 mmol, P < .05), butyrate (SHyd 63 vs SNat 17 mmol, P < .01), isovalerate (SHyd 17 vs SNat 5 mmol, P < .05), and acetate (SHyd 298 vs SNat 219 mmol, P < .13). There were no significant changes in insulin and glucagon production. Intake of the maltitol-rich diet resulted in less available energy (82.0%) than did intake of the maltose-rich diet (92.6%).

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The nutritive value of two nitrogen-containing mixtures, one formed from small peptides (milk protein mild enzymatic hydrolysates) and the other consisting of a mixture of free amino acids having the same pattern except for glutamine, was measured in rats with and without experimental liver and exogenous pancreas dysfunction. For this purpose, 30 animals (group N) were fitted with an indwelling duodenal catheter; 36 animals (group L) also underwent ligation and resection of the biliopancreatic duct. After a 3-day recovery period, the animals in each group, divided into three equivalent batches, were given, for 10 days, a protein-free diet ad libitum and a twice-daily duodenal infusion (5 mL) of either saline, the small peptides, or the free amino acid mixture. The nitrogen-containing mixtures provided 0.32 g of nitrogen per day. A blood sample (left side of the heart) was collected 1 hour before (five to six animals per batch) and after (five to six animals per batch) the last infusion for determination of glucose, insulin, and amino acids. After the animals were killed, their carcasses were freeze-dried, ground, and analyzed for nitrogen content. Under these conditions, the net protein utilization (the gain in body nitrogen in the animals infused with one of the two nitrogen-containing solutions in comparison with the animals infused with saline only divided by the nitrogen ingested) was calculated.(ABSTRACT TRUNCATED AT 250 WORDS)

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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.

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The aim of the present study was to measure the incorporation of infused 15N in blood fractions, urine, digesta, faeces and in the exocrine pancreatic and biliary secretions, in order to estimate the endogenous part of nitrogen in the ileal digesta and in the faeces of pigs fed a casein diet and to calculate the total endogenous nitrogen secretion as well as its recycling in the digestive tract. For 8 d 11 Large White female pigs (50.1 +/- 1.8 kg) received a continuous infusion of L-[15N]leucine via a catheter in the jugular vein. The 15N-enrichment was measured in several fractions. The 15N-level of the pancreatic juice was higher than that in the biliary secretion, TCA-blood fractions, and urine during the whole experimental period. Using the 15N-isotope dilution method it was found that casein was completely digested up to the terminal ileum and that all the nitrogen in the ileal digesta was of endogenous origin. The total endogenous secretion was estimated at approximately 11 g N/d. The reabsorption of endogenous nitrogen amounted to 79% up to the end of the small intestine and 88% over the whole digestive tract.

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The intestinal absorption of glucose and alpha-amino nitrogen, the appearance of D-and L-lactic acids in the protal vein and the consumption of oxygen by the organs of the abdominal extrahepatic splanchnic area were studied simultaneously in pigs either during the postprandial period or during a fasting period of the same length. For this purpose, 5 growing pigs (59.4 +/- 3.5 kg live weight) were fitted with permanent catheters in the portal vein and carotid artery and with an electro-magnetic flowmeter probe around the portal vein. This device was used to measure the exchanges between the blood and the intestinal lumen. For a period of 1 wk, the animal received a semi-synthetic diet containing 6% purified cellulose (R6) and then during the next wk, a diet containing 16% purified cellulose (R16), the order of distribution being alternated from one animal to the next. During each of these 2 wk and after a fasting period of 16 h, they were subjected to 2 successive tests of 5 h, either after intake of an 800-g meal (R) (R6 or R16), or after no meal intake (J6 or J16). During these tests, blood samplings were made at 15 to 30-min intervals, the consumption of oxygen was recorded by an ABL3 radiometer and the afore mentioned nutrients and metabolites analysed in these samples. The consumption of oxygen was higher (P > 0.01) during the postprandial period (5.41 +/- 0.19 mmol/kg/h) than during the fasting period (4.64 +/- 0.19 mmol/kg/h) while the availability of oxygen only increased slightly (P < 0.05) (14.01 +/- 0.66 vs 13.08 +/- 0.76 mmol/kg/h). By contrast, the oxygen extraction coefficient did not significantly increase with meal intake. The appearance of L-lactic acid in the portal blood was higher (P < 0.001) during the postprandial period (3.83 +/- 0.32 g/h) than during the fasting period (1.23 +/- 0.23 g/h). The energy expenditure due to the aerobic metabolism of the organs drained by the portal vein ranged from 35.7 to 37.8 kcal/h after meal intake, ie 1-18% more than after fasting. The anaerobic metabolism only represented 0.3-0.4% (fasting) and 1.1-1.3% (postprandial period) of this aerobic metabolism. Oxygen consumption was not changed by the dietary cellulose content.

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