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Hepatic and intestinal balances of amino acids, insulin, glucagon and gastrin were studied in 6 non-anaesthetized Large White pigs (mean body weight 64 +/- 4.8 kg) after ingestion of casein or rapeseed proteins. The animals were fitted with permanent catheters in the portal vein, the brachiocephalic artery and the right hepatic vein. In addition, 2 electromagnetic flow probes were implanted, one around the portal vein and the other around the hepatic artery. After a preliminary adaptation to each diet the animals received at 1-wk intervals and according to a double latin square design, 3 test meals of 800 g each, one containing 23.2% of rapeseed concentrate (diet RA 12) and the others 13.9 or 27.8% of hydrochloric casein (diets CA 12 and CA 24). Each observation period lasted 12 h. Amino acids from all diets were very well absorbed. In 12 h, the absorption of total amino acids as a percentage of the ingested quantities was 99% for CA 12, 102% for CA 24 and 104% for RA 12. Hepatic uptake of total amino acids in 12 h expressed as a percentage of the absorbed quantities was 13% for CA 12, 66% for CA 24 and 25% for RA 12. Differences in the hepatic extraction rate of essential amino acids appeared between the 2 levels of casein ingestion and for Arg between the 2 protein sources. Whatever the nature of the ingested protein or the level of casein, the liver showed a net production of Asp and Glu. The production and hepatic balance of insulin were the lowest after ingestion of RA 12. No differences were noted in the same parameters for glucagon and gastrin. Independently of the nutritional situation, the hepatic extraction rate of insulin appeared to be higher than those of glucagon and gastrin. Our results showed that the nature as well as the level of dietary proteins have large effects on the sequence and volume of absorptive phenomena, the hepatic metabolism of nutrients, the production of gastrointestinal hormones and the non-hepatic tissue disposal of absorbed nutrients.

We studied the apparent digestibility of an ad libitum diet in 16 growing rabbits, 8 with pancreatic duct ligature (P-) and 8 sham-operated (TO). The study was divided into two 10-day periods, starting 5 and 33 days, respectively, after surgery. The food intake of the sham-operated animals was higher (160 g/day at the end of the experiment) than that of the ligated ones (stabilized at 100-120 g/day); mean daily gain was also higher in the former (TO: 33.7 g/day, P-: 15.6 g/day; P less than 0.01). Dry matter (MS) and energy digestibilities were not significantly different in the P- and the TO groups, but nitrogen (N) digestibility, decreased after pancreatic duct ligature (TO: 86.1, P-: 64.9; P less than 0.01), then increased in time much more in P- than in sham-operated rabbits, but remained lower in the ligated group (-5.6 points). The results suggest that digestive compensation was established after pancreatic duct ligature; its origin is hypothesized.

Even though the availability of dietary amino acids is the result of integrated phenomena of digestion, absorption and transport, it may be mainly affected by the stage of luminal digestion. In this case, amino acid availability could be predicted by an in vitro method designed to reproduce in vivo proteolysis conditions. In order to check this hypothesis, the essential amino acid (EAA) profiles of digesta collected at 8 intervals during a 24-h in vitro enzymatic proteolysis of casein and rapeseed proteins were compared to the pattern of appearance of dietary EAA in portal vein of pigs fed the same proteins, determined at each hour over a 8-h postprandial period by coupling blood flow rate with porto-arterial differences in plasma EAA concentrations. Comparisons of in vitro and in vivo data first bore on overall EAA profiles measured at each interval, and then on the individual kinetics of each EAA. Regarding total profiles, the highest correlations for casein (r: 0.80-0.98) were found when comparing EAA patterns determined during the first half of in vitro digestion and in vivo absorption periods. Similar r values were obtained with rapeseed proteins, but over longer periods of measurement. Concerning individual kinetics, the highest correspondences were found with rapeseed proteins, with 5 out of 9 EAA (methionine, isoleucine, leucine, phenylalanine and arginine) having their in vitro sequence of release significantly correlated with their in vivo sequence of absorption. With casein, correlations were significant for threonine, valine, isoleucine and leucine. These results suggest that sequential hydrolysis in the digestive tract, as reproduced by the in vitro technique, is a key determinant of amino acid appearance in the portal blood to a degree varying with the protein source and with the nature of the amino acid.

The aim of this study was to determine the rate of circulating gastrointestinal hormones in pigs when pancreatic secretion was re-introduced or removed from the duodenal lumen. Permanent fistulas were fitted into the pancreatic duct and duodenum of 16 pigs, and catheters were introduced into the portal vein and a jugular vein as well. Plasma hormone content was determined at different times during two periods of 30 and 60 min each, when the juice was returned to the pigs; these two periods included a 120-min interval when the juice was not reintroduced into the intestinal lumen. When the pancreatic juice was not returned to the pigs, plasma secretin content rose significantly in the portal blood (+ 42.8% at min 15; +52.5% at min 30; +31% at min 60 and +27% at min 120) and in the peripheral blood (+36.4% at min 30; +18.9% at min 120) compared to the mean values recorded during intraduodenal re-introduction of the secretion. In parallel, the volume of juice secreted and protein output increased significantly but their concentration did not. When the pancreatic juice was removed the mean cholecystokinin level in the portal vein did not change significantly, except at min 30 when its value was 32% higher than the mean during the periods of restitution. Cholecystokinin in the peripheral blood was not affected by removing the pancreatic juice from the intestinal lumen. The mean plasma levels of gastrin, somatostatin, VIP and PP in the portal and peripheric blood were unaltered. These results suggest that in pigs secretin may have an important role in the regulation of pancreatic secretion by negative feedback.

The intestinal absorption of nitrogen from amino acids present in a solution of small peptides or of free amino acids with the same pattern, perfused intraduodenally, has been studied using two analytical techniques [2, 4, 6 trinitrobenzene-1-sulfonic acid (TNBS) after dialysis of the blood vs ninhydrine after chromatography] to determine post-perfusion porto arterial differences and to measure blood flow rate in the portal vein. The results obtained on blood nitrogen level with the chromatographic method were always higher than those obtained using the TNBS method. The differences in the values varied from 8 to 24% according to post-perfusion time and to blood sample origin (arterial or portal). On the contrary, the absorbed amounts of nitrogen measured by either analytical technique were not very much different: no significant and systematic deviation was found between the two. The TNBS method is thus useful as a preliminary approach to very elaborate studies on intestinal absorption. In these conditions, the nitrogen of amino acids from duodenally-perfused small peptides was absorbed earlier and more rapidly than that from a perfusion of a solution of free amino acids. The amount of nitrogen appearing in the portal vein five hours after perfusion exceeded the perfused amount owing to considerable recycling of endogenous nitrogen.

The effects of intravenous glucose perfusion were studied in the pancreatic juice of fistulated pigs. Perfusions were performed either discontinuously for 3 hrs in the fasted or for 6 hrs a day over 6 days in the fed animal. Pancreatic juice volume, total proteins and total activities of chymotrypsin, amylase and lipase were always significantly lowered by glucose given intravenously. Amylase seemed to be the most inhibited of the three enzymes studied. It appeared that prolonged intravenous glucose perfusion could not reproduce in the pig the pancreatic amylase adaptation seen after oral administration of glucose.

The digestive physiology of the germ-free animal has a number of characteristics (cecal hypertrophy, slower small intestine cell renewal, slower gastric emptying and intestinal transit) which distinguish it from that of the conventional animal. If the germ-free model is to be used to determine the role of gastrointestinal microflora in the nutrition of the conventional animal, it is essential to complete the study of these characteristics by data on digestive enzymes in the germ-free. The present paper analyzes these data. There is little information on salivary amylase and none on gastric proteolytic enzymes and intestinal peptidases. More complete data on exocrine pancreas enzymes and intestinal disaccharidases show that the digestive equipment is similar in germ-free and conventional animals. Bile salts, not considered as digestive enzymes, are qualitatively and quantitatively different, depending on the digestive tract bacterial environment. In general, the germ-free animal has some characteristics which should permit better utilization of the diet ingested. Measurements of apparent digestibility do not confirm this hypothesis since results obtained in germ-free and conventional animals of the same species are contradictory.

The aim of the present work was to study, in the unstressed catheterized gilt, the effect of pregnancy on arterial substrate and pancreatic hormone concentrations in relation to the feed intake level. The experiments were performed on 14 pregnant gilts during the last month of gestation and 5 non pregnant gilts after cannulation of one carotid artery. Blood samples have been collected regularly after an overnight fast. After catheterization of the pregnant gilt, a 4 day-period is required to obtain steady-state conditions. As compared with non-pregnant animals fed on the same standard conditions (i.e. 2 kg/d: crude protein: 130 g/kg; digestible energy: 12.8 MJDE/kg), pregnant gilts exhibit similar and constant blood glucose, lactate, ketone body and plasma free fatty acid concentrations. By contrast, blood alanine concentrations progressively increases. A reduction of the feed intake level by 40% does not modify the blood glucose concentrations but leads to reduce blood lactate and alanine concentrations. On the contrary, plasma free fatty acid levels rise progressively with a limited increase in blood ketone body concentrations. While plasma glucagon concentrations are constant whatever the physiological state or the feed intake level, plasma insulin levels progressively decrease in the pregnant gilt. These data are discussed to display some aspects of the adaptation of the maternal metabolism in the gilt in late gestation.

The purpose of the present study was to examine the adaptation of pancreatic lipase to the amount and nature of dietary lipids in the growing pig. Thirty pigs were distributed into three groups of 10 animals each. They were fed the same amount (1.5 kg/pig/day) of either diet C (3.5% lard, 3.5% sunflower oil, 67.7% starch), diet L (21% lard, 33.2% starch) or diet SO (21% sunflower oil, 33.2% starch) for 12 days. The diets were isoenergetic and isonitrogenous. Pancreas weight relative to live-weight was highest in group L. The pancreatic lipid content of the latter group exceeded that of groups C and SO by 53 and 39%, respectively. The pancreatic protein content was similar in the three groups. The specific lipase activity of pancreatic tissue (U per mg of protein) in group SO was about 1.6-fold higher than that of group L and about 3-fold higher than that of group C (31.9, 19 and 11.6, respectively). Specific amylase activity was higher in animals of group C than in those of the other two groups (C : 1689; L : 1112; SO : 984), whereas no difference was observed in chymotrypsin activity. Specific trypsin activity was lowest in group L. These results confirm the adaptation of pancreatic lipase and amylase to their respective substrates. Furthermore, it appears that lipase activity was more or less affected by the degree of unsaturation of lipids and that it was much higher for the same amount of triacylglycerols when the latter were rich in unsaturated fatty acids. The mechanisms involved have not been determined yet, but the possible physiopathological consequences of the increased pancreatic lipid content observed in pigs receiving triacylglycerol-rich diets (including especially saturated fatty acids) should be considered.

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