Long-term intermittent glutamine supplementation repairs intestinal damage (structure and functional mass) with advanced age: assessment with plasma citrulline in a rodent model.

OBJECTIVE: Glutamine is the preferred fuel for the rat small intestine and promotes the growth of intestinal mucosa, especially in the event of gut injury. Quantitatively, glutamine is one important precursor for intestinal citrulline release. The aim of this study was to determine whether the effect of glutamine on the increase in intestinal villus height is correlated with an increase in both gut mass and citrulline plasma level in very old rats. METHODS: We intermittently supplemented very old (27-mo) female rats with oral glutamine (20% of diet protein). Intestinal histomorphometric analysis of the small bowel was performed. Amino acids, in particular citrulline, were measured in the plasma, liver and jejunum. Markers of renal (creatinine, urea) and liver (alanine aminotransferase [ALT]) and aspartate aminotransferase (AST) functions were measured to evaluate renal and liver functions in relation to aging and to glutamine supplementation. Liver glutathione was also determined to evaluate cellular redox state. RESULTS: Glutamine supplementation maintains the body weight of very old rats, not by limiting sarcopenia but rather by increasing the organ mass of the splanchnic area. Total intestine mass was significantly higher in glutamine-supplemented rats than in controls (15%). Measurement of villus height and crypt depth demonstrated that the difference between villus and crypt was significantly improved in glutamine pre-treated rats compared to controls (~ 11%). Plasma citrulline also increased by 15% in glutamine-supplemented rats compared to controls. CONCLUSION: Citrulline appears as a biomarker of enterocyte mass in villous atrophy associated with advanced age. Non-invasive measurement of this metabolite may be useful in following the state of the gastrointestinal tract in very old people, whose numbers are increasing worldwide and the care of whom is a major public health issue. The gut may contribute to the malnutrition caused by malabsorption frequently observed in the elderly.

Effect of intermittent glutamine supplementation on skeletal muscle is not long-lasting in very old rats.

BACKGROUND AND OBJECTIVE: Muscle is the major site for glutamine synthesis via glutamine synthetase (GS). This enzyme is increased 1.5-2 fold in 25-27-mo rats and may be a consequence of aging-induced stress. This stimulation is similar to the induction observed following a catabolic state such as glucocorticoid treatment (6 to 24 months). Although oral glutamine supply regulates the plasma glutamine level, nothing is known if this supplementation is interrupted before the experiment. DESIGN: Adult (8-mo) and very old (27-mo) female rats were exposed to intermittent glutamine supplementation for 50 % of their age lifetime. Treated rats received glutamine added to their drinking water and control rats water alone but the effect of glutamine supplementation was only studied 15 days after the last supplementation. RESULTS: Glutamine pretreatment discontinued 15 days before the experiment increased plasma glutamine to ~ 0.6 mM, a normal value in very old rats. However, it failed to decrease the up-regulated GS activity in skeletal muscle from very old rats. CONCLUSION: Our results suggest that long-term treatment with glutamine started before advanced age but discontinued 15 days before rat sacrifice is effective in increasing plasma glutamine to recover basal adult value and in maintaining plasma glutamine in very old rats, but has no long-lasting effect on the GS activity of skeletal muscle with advanced age.

Protein requirements in male adolescent soccer players.

Few investigations have studied protein metabolism in children and adolescent athletes which makes difficult the assessment of daily recommended dietary protein allowances in this population. The problematic in paediatric competitors is the determination of additional protein needs resulting from intensive physical training. The aim of this investigation was to determine protein requirement in 14-year-old male adolescent soccer players. Healthy male adolescent soccer players (N = 11, 13.8 +/- 0.1 year) participated in a short term repeated nitrogen balance study. Diets were designed to provide proteins at three levels: 1.4, 1.2 and 1.0 g protein per kg body weight (BW). Nutrient and energy intakes were assessed from 4 day food records corresponding to 4 day training periods during 3 weeks. Urine was collected during four consecutive days and analysed for nitrogen. The nitrogen balances were calculated from mean daily protein intake, mean urinary nitrogen excretion and estimated faecal and integumental nitrogen losses. Nitrogen balance increased with both protein intake and energy balance. At energy equilibrium, the daily protein intake needed to balance nitrogen losses was 1.04 g kg(-1) day(-1). This corresponds to an estimated average requirement (EAR) for protein of 1.20 g kg(-1) day(-1) and a recommended daily allowance (RDA) of 1.40 g kg(-1) day(-1) assuming a daily nitrogen deposition of 11 mg kg(-1). The results of the present study suggest that the protein requirements of 14-year-old male athletes are above the RDA for non-active male adolescents.

Small peptides (<5kDa) found in ready-to-eat beef meat.

Dietary proteins can have biological properties, many attributed to bioactive peptides (2-50 amino acids). Since little is known about peptides in meat, we investigated the postmortem occurrence of low molecular weight peptides (<5kDa) in bovine Pectoralis profundus muscle, after 14 days storage at 4°C and vacuum cooking for 90min at 75°C. The study combined quantitative (amino acid analysis) and qualitative approaches (mass spectrometry). Eighty-nine percent of peptidic amino acids in fresh muscle corresponded to carnosine, anserine and glutathione. Levels of these compounds were lower in cooked meat compared to fresh muscle. Concomitantly, numerous larger compounds, most probably peptides, were generated in a very reproducible manner during ageing and even more during cooking of meat. Seven peptides (fragments of troponin T, nebulin, procollagen and cypher proteins) were identified in cooked meat extracts.

Calcium overload increases oxidative stress in old rat gastrocnemius muscle.

In order to challenge in vivo muscle Ca2+ homeostasis and analyze consequences on mitochondrial H2O2 release (MHR) and sarcopenia, we injected Ca2+ ionophore A23187 (200 microg/kg, ip) in adult and old rats and measured gastrocnemius mass and mitochondrial Ca2+ content (MCC) using radioactive Ca2+ 48 h after injection. In a second experiment performed in old rats, we measured isocitrate dehydrogenase (ICDH) activity as an index of MCC, MHR, mitochondrial respiration, citrate synthase, COX and antioxydant enzyme activities 24 h after a 150 microg/kg injection. In adult rats, muscle mass and MCC were unchanged by A23187. In old rats, MCC increased 24 h after injection as reflected by a significant increase in ICDH activity; measured MCC tended to increase at 48 h. MHR and Mn-SOD activity were significantly increased at 24 h, and GPX activity was reduced. Muscle mass was unchanged but was negatively correlated with MCC in control and treated old rats. In conclusion, in old rats, A23187 probably induced a mitochondrial Ca2+ overload responsible for the observed increase in MHR without leading to muscle atrophy on a short term basis.

Glucocorticoid effects on insulin- and IGF-I-regulated muscle protein metabolism during aging.

This study was performed to assess the effect of glucocorticoids (dexamethasone) on insulin- and IGF-I-regulated muscle protein metabolism in adult and old rats. Muscle atrophy occurred more rapidly in old rats, and recovery of muscle mass was impaired when compared with adults. Muscle wasting resulted mainly from increased protein breakdown in adult rat but from depressed protein synthesis in the aged animal. Glucocorticoid treatment significantly decreased the stimulatory effect of insulin and IGF-I on muscle protein synthesis in adult rats by 25.9 and 58.1% respectively. In old rats, this effect was even greater, being 49.3 and 100% respectively. With regard to muscle proteolysis, glucocorticoids blunted the anti-proteolytic action of insulin and IGF-I in both age groups. During the recovery period, adult rats reversed the glucocorticoid-induced resistance of muscle protein metabolism within 3 days, at which time old rats still exhibited the decrease in insulin-regulated proteolysis. In conclusion, the higher sensitivity of old rat muscle to glucocorticoids may in part result from the greater modification of the effects of insulin and IGF-I on muscle protein metabolism. These responses to glucocorticoids in old rats may be associated with the emergence of muscle atrophy with advancing age.

A high protein diet does not improve protein synthesis in the nonweight-bearing rat tibialis anterior muscle.

We recently demonstrated that a high protein intake partially prevented the decrease in protein synthesis in the atrophied dark soleus muscle of rats that were hindlimb suspended (HS) for 21 d. To study the possible role of protein intake in a muscle more representative of the whole musculature, we measured the effect of a high protein (HP) (30%) and a medium protein (MP) (15%) diet on protein synthesis in the pale fast-twitch tibialis anterior muscle of HS rats. The HS animals were suspended by the tail for 21 d so that only their front legs were able to rest on the floor. The fractional rate of protein synthesis (Ks) was determined in vivo using a flooding dose method. A significantly lower Ks (24-25%) was found in both HS-MP and HS-HP rats compared with their pair-fed control groups. Reduced Ks in HS-MP rats relative to their pair-fed controls resulted from a decrease in the translational efficiency (KRNA, 23%, P < 0.01), while the ratio of RNA to protein (Cs) was unaffected. In contrast, the decrease in KRNA was prevented in the HS-HP animals compared with their pair-fed controls (P < 0.05). Hindlimb suspension did not alter fiber type distribution in the tibialis anterior muscle. However, a higher proportion of intermediate and Type I fibers with a concomitant decrease in Type II fibers was observed in both CT and HS animals fed the HP diet compared with those fed the MP diet (P < 0.05). These data clearly establish that depressed protein synthesis contributes to altered protein accretion in fast-twitch muscles during long-term hindlimb suspension. Although the HP diet prevented the decrease in translational efficiency in muscles from HS rats, it neither sustained protein synthesis nor prevented the reduction in muscle growth. Thus, it seems very unlikely that a high protein diet had any beneficial effect on the overall musculature during weightlessness in rats.

Age-related changes in protein synthesis measured in vivo in rat liver and gastrocnemius muscle.

This study analyses in detail the effects of ageing on gastrocnemius muscle and liver protein synthesis measured in vivo at three ages, 1.5 months (young), 12 months (adult) and 24 months (old) in Sprague-Dawley rats. Comparing adult and old rats, muscle protein synthesis was decreased in old rats when expressed per unit of RNA and per day (translational efficiency), was unchanged when expressed in absolute terms and increased when expressed in fractional terms as a result of protein loss due to muscle atrophy. In the liver, only translational efficiency tended to decrease in old rats compared to adult rats. It is concluded that the decline in protein turnover described in vitro is consistent with a decrease in translational efficiency, but that absolute synthesis rates are maintained during ageing. Muscle atrophy is unlikely to result from alterations in protein synthesis pathways.

[Transport of amino acids in the splanchnic bed by blood plasma and blood in the preruminant calf]. / Transport des acides aminés dans l'aire splanchnique par le plasma sanguin et le sang chez le veau préruminant.

Three preruminant calves were fitted with catheters in portal and hepatic veins and in a mesenteric artery. Two electromagnetic flowmeter probes were clipped around the portal vein and the hepatic artery. The calves were fed either a diet with a low (L) or a high (R) abomasal emptying rate for dietary proteins. Blood flow and free amino acid levels in plasma (P) and blood (S) were determined before the morning meal and during the following 7 h. In the portal vein, for most amino acids P/S ratios were correlated to the net amino acid balance of the digestive tract measured in plasma. By contrast in the hepatic vein, these ratios were mainly correlated to hepatic balance measured in whole blood. Correlations between digestive tract and hepatic balance calculated using either plasma or whole blood pool were different for some amino acids. This suggests that amino acid exchange between plasma and blood cells is low and absorbed amino acids are mainly transported to the liver by plasma, whereas whole blood rather than plasma is concerned in amino acid exchanges in the liver.

Yield and composition of milk from lactating mares: effect of lactation stage and individual differences.

The yields and composition of milk from nursing mares were studied during the first two months of lactation in 11 mares of heavy breeds (784 kg). Daily yield increased from 21.7 to 24.6 kg between weeks 1 and 8 of lactation. Fat, protein, gross energy and Ca concentrations significantly decreased when lactose content increased during this period. Individual variations were higher for yield than for composition. Casein, whey protein and non-protein N (56, 34 and 10% of crude protein, respectively) and amino acid composition did not vary between weeks 1 and 8 of lactation.

[Protein metabolism in the newborn lamb. IV. Consequences of amino acid and lactose ingestion]. / Métabolisme protéique de l'agneau nouveau-né. IV. Conséquences de l'ingestion d'acides aminés et de lactose.

A study was made on protein metabolism and hormonal changes following birth in newborn lambs fed amino acids alone or in combination with lactose. Eight newborn lambs taken from their mother immediately after birth were fed hourly for 8 h, either with a solution of peptides and free amino acids obtained by mild hydrolysis of whey proteins (4 lambs; diet AP) or with the same solution + lactose (4 lambs; diet APL). L-[4,5-3H] leucine was continuously perfused into a jugular vein for 6 h when the lambs were 2 h 30 min old. Plasma glucose and insulin levels increased after birth in APL lambs whereas they decreased in the AP; these differences were significantly different. Plasma cortisol levels remained unchanged throughout the experiment. Free essential amino acid levels did not vary when lambs were older than 4.5 h; they depended on the corresponding amino acid intakes. Plasma free threonine, valine, isoleucine, leucine, tyrosine and lysine were lower in APL than in AP lambs. The plasma leucine irreversible loss and leucine oxidation were higher in AP than in APL lambs. The plasma flux of leucine from whole body protein breakdown was lower in APL than in AP lambs inasmuch as the plasma flux of dietary leucine may be estimated by the amounts of leucine ingested in both cases. No significant difference was found for the fractional synthesis rates of tissue proteins such as liver, skin, skeletal muscle, lung, brain and whole body. These rates for skin, muscle and whole body were close to those previously measured in colostrum fed lambs. The increase in whole body protein accretion resulting from lactose feeding in combination with amino acids seemed to result from a decreased protein breakdown that could be mediated by the insulin response.

Effect of colostrum feeding on protein metabolism in the small intestine of newborn lambs.

In a first experiment with 24 newborn lambs, the promoting effect of colostrum feeding on the fresh weight of the small intestine and its protein content was demonstrated by comparison with that of other dietary treatments (fasting, lactose, protein hydrolysate feeding). In a second experiment, the amounts of colostral IgG1 entrapped within the intestine wall and the valine incorporation rates into the intestinal protein were determined in 3-, 8- and 18-hour-old lambs fed either cow milk, cow colostrum or ewe colostrum. The amounts of IgG1 in the small intestine wall and the valine incorporation rates were higher in the lambs fed colostrum (ewe or cow) than in the milk-fed animals. The intestinal protein increase resulted primarily from the retention of colostral proteins in the colostrum-fed newborn lambs. However, colostrum feeding stimulated intestinal protein synthesis more actively than milk feeding.

Dietary control of protein turnover.

The balance between protein synthesis and breakdown (protein turnover) regulates whole-body protein mass. The relationships between dietary changes (amount and composition of food) and protein synthesis, protein breakdown and amino acid oxidation have been explored in order to better understand adaptations of protein and amino acid metabolism. Methods for measuring protein synthesis, especially whole-body protein synthesis, can be divided into two groups: the 15N end-product method (urea and/or ammonia), and the incorporation of labelled amino acid(s) into proteins. Assumptions and limitations of the widely used two-pool model (free amino acid and protein pools) are discussed. Results obtained with different methods and for amino acids have been compared, to assess their ability to detect changes in protein synthesis rates. Methods of measuring protein breakdown have also been described briefly. Food intake affects whole-body and tissue protein turnover throughout development of animals and humans in different ways. Protein metabolism fluctuates during the 24-hour period in response to intermittent food intake. During the post-prandial period, a net whole-body protein deposition occurs. This is essentially due to increased protein synthesis. The free amino acid pool and amino acid oxidation rates also increase. Consequently, amino acids are used to a great extent as energy substrates. In contrast, a decrease in protein breakdown could enhance protein deposition. During fasting, the rates of whole-body protein synthesis are lower than those of protein breakdown. This results in protein loss, essentially because the drop in protein synthesis rate in muscle is pronounced. N balance is controlled by the amounts and composition of the diet and by changes in protein synthesis and breakdown. Increasing food intake above levels of energy equilibrium can produce growth by enhancing both the whole-body protein synthesis and breakdown rates. Below energy equilibrium, whole-body protein loss occurs because of decreased protein synthesis which becomes lower than protein breakdown. Protein synthesis rate is the main factor controlling N balance in response to alterations in food intake. Increasing dietary protein, especially the essential amino acids, involves increased rates of whole-body protein synthesis and breakdown. The improved N balance obtained by enhancing dietary non-protein energy (carbohydrate, fat) can be brought on by reducing amino acid oxidation and slightly increasing protein synthesis. The effects of dietary protein and energy on protein turnover are apparently additive.

[Digestion of milk proteins and metabolism of methionine in the newborn lamb]. / Digestion des protéines de lait et métabolisme de la méthionine chez l'agneau nouveau-né.

Methionine absorption and catabolism were studied in 4 newborn lambs during the first 8 h after birth. Lambs were hourly fed 50 ml goat milk labelled with 35S-methionine and 35S-cysteine. The free amino acid levels and the specific activity of free methionine were measured in jugular blood samples collected 1 h (just before the first meal), 4, 6 and 8 h after birth and in the portal blood 8 h after birth. Specific activities of protein-bound methionine and cysteine were measured in the milk and then in the abomasal and intestinal contents as well as in the liver, intestine and whole body proteins, 8 h after birth. The jugular blood levels of free valine, isoleucine, leucine, phenylalanine and histidine increased significantly between 1 and 8 h whereas the levels of free alanine, serine, glycine, citrulline and 3-methylhistidine decreased. The concentrations of most free amino acids were 30% higher in portal than in jugular blood. In the abomasal contents, the specific activities of methionine and cysteine were 96 and 168%, respectively of that of ingested milk and in the intestinal contents the corresponding values were 24 and 31% (table 1). In the jugular blood, the specific activity of methionine reached a plateau before 5 h after the first meal; in the portal blood 8 h after birth it represented 75% of the specific activity entering the small intestine. The blood methionine flux was calculated according to two methods: from whole-body protein synthesis rates and methionine catabolism and from the irreversible loss of blood methionine (table 2).(ABSTRACT TRUNCATED AT 250 WORDS)

Digestion of milk, fish and soya-bean protein in the preruminant calf: flow of digesta, apparent digestibility at the end of the ileum and amino acid composition of ileal digesta.

1. Digesta were collected from eleven preruminant calves fitted with re-entrant (four calves in Expt 1 and three in Expt 2) or single cannulas (four calves in Expt 1) in the terminal ileum. Collection periods lasted 24 h (Expt 1) or 96 h (Expt 2). 2. Two milk-substitutes (fish and soya bean) and a control diet were given to the calves. In the control diet, protein was entirely provided by skim-milk powder. In the other two diets, protein was provided mainly by a partially hydrolysed white-fish protein concentrate or a soya-bean protein concentrate prepared by extracting soya-bean meal with hot aqueous ethanol. 3. In Expt 1, flow rates of fresh matter, dry matter, nitrogen and ash exhibited two maxima between 6 and 8 h after the morning meal and between 4 and 6 h (control and soya-bean diets) or 6 and 8 h (fish diet) after the evening meal. Minimum pH values were observed at times of maximum flow rate. Variations observed in the flow rates and pH values were larger with fish and especially soya-bean diets than with the control diet. 4. The apparent digestibility of the three diets in the terminal ileum was significantly higher in Expt 2 than in Expt 1: for N, the values were 0.92, 0.83 and 0.75 (Expt 1), and 0.94, 0.87 and 0.88 (Expt 2) with the control, fish and soya-bean diets respectively. 5. The amount of N apparently absorbed in the terminal ileum represented 90-96% of the amount that disappeared from the whole digestive tract in Expt 1 and 95-99% in Expt 2. 6. In Expt 1 the amino acid (AA) composition of digesta changed little with the flow rate when the calves were given the control diet (from 158 to 179 g glutamic acid/kg AA). With the fish and soya-bean diets the AA composition was similar to that observed with the control diet when the flow rate was minimum, but differences became apparent as the flow rate increased (281 and 161 g glutamic acid/kg AA for the soya-bean and control diets respectively with maximum flow rate). In Expt 2, the mean compositions of the digesta were very similar to the means obtained in Expt 1. 7. Different comparisons with dietary, endogenous and bacterial proteins indicated that for the three diets a common mixture containing approximately 65% endogenous and 35% bacterial proteins reached the terminal ileum.(ABSTRACT TRUNCATED AT 400 WORDS)

[Effects of lactose ingestion on protein metabolism in the newborn lamb]. / Influence de l'ingestion de lactose sur le métabolisme protéique de l'agneau nouveau-né.

Whole body and tissue protein turnovers were measured in 6 newborn lambs taken from their mothers immediately after birth. Three lambs (AJ) were hourly fed 50 ml of saline (NaCl 0.9%), and 3 (AL) were fed, on the same schedule, 50 ml of saline with 2.25 g of lactose added. They were continuously infused L-[4,5(3)H]-leucine for 6 h when they were 2 h 30 min old. Plasma glucose and insulin were higher in AL than in AJ lambs. On the contrary, the lowest plasma levels of free threonine, valine, isoleucine, leucine, phenylalanine, lysine, histidine, serine and alanine occurred in the lactose-fed lambs (table 1). The concentrations of most free amino acids in liver, brain, small intestine and muscle (Longissimus dorsi) were not significantly different (fig. 1). The irreversible loss of plasma leucine did not differ (mean +/- SD : 160 +/- 47 and 156 +/- 11 micro moles/h/kg for AL and AJ lambs, respectively). The leucine catabolic rate was higher in AJ than in AL lambs (22.4 +/- 2.8 vs 17.9 +/- 1.7%). The fractional rates of protein synthesis in the liver, small intestine and brain were not significantly different between AL and AJ lambs; these rates were higher in the muscle, lungs and whole body of the AL lambs (table 2).

[Protein metabolism in the newborn lamb. I. Impact of the ingestion of colostrum on blood glucose, blood levels of gammaglobulin and free amino acids in tissues]. / Métabolisme protéique de l'agneau nouveau-né. I. Conséquences de l'ingestion de colostrum sur la glycémie, la gammaglobulinémie et les teneurs en acides aminés libres des tissus.

Ten newborn lambs were divided into two groups at birth. Five of them were fed hourly with cow colostrum; the others (unfed lambs) were given saline. Jugular blood levels of glucose, urea, free amino acids and IgG1 were measured during the 10-hour period following birth. The lambs were then exsanguinated under pentobarbital anaesthesia. Free amino acid levels were determined in liver, muscle (longissimus dorsi) and skin. The glycogen contents of the liver and whole body were measured. The IgG1 levels were determined in the intestinal wall and in the contents of the abomasum and small intestine. The blood glucose levels increased after birth in both groups and did not differ significantly in either group. After colostrum feeding, hepatic glycogen and blood urea concentrations were higher in fed than in unfed lambs. Blood free essential amino acid levels which increased after birth in the fed group, were higher in that group than in the unfed one. Nonessential free amino acid levels remained nearly constant throughout the experimental period and did not differ significantly in either group (fig. 2). Free threonine and valine in the liver, skin and muscle were higher in the colostrum-fed lambs than in the others. IgG1 levels increased after birth in the blood of the fed lambs and seemed to be closely related to the intestinal contents of these compounds (fig. 3). The amount of blood free essential amino acids provided by the hydrolysis of colostral proteins was estimated at about 43% of the amount entering the small intestine.

[Protein metabolism in the newborn lamb. II. Influence of diet on protein synthesis and turnover]. / Métabolisme protéique de l'agneau nouveau-né. II. Influence de l'alimentation sur les flux et le taux de renouvellement des protéines.

Leucine turnover and protein fractional synthesis rates were measured in fed and unfed newborn lambs. The fed group (4 animals) was fed hourly with cow colostrum throughout the experiment which started at birth; the unfed group (5 animals) was given saline (NaCl 9 0/00). Two hours after birth, L-(1-14C) leucine was infused into the jugular vein at a constant rate for 8 h. Eight blood samples were taken during the infusion period; at the end of the experiment, the liver, skin and three muscles (supraspinatus, longissimus dorsi, tensor fasciae latae) were sampled. The specific activity of free and protein-bound leucine was measured in these samples and in the whole body (table 2). The specific activity of free leucine reached a quasi-steady state in the plasma within 2 h after the beginning of infusion (fig. 1). The irreversible loss rate of plasma leucine and the leucine catabolic rate were higher in fed than in unfed lambs. The highest fractional rates of protein synthesis occurred in the liver, skin and whole body (table 3). They were similar in both groups. In contrast, fractional rates of protein synthesis in muscles were higher in fed than in unfed animals. Thus, the proportion of whole body protein synthesis, accounted for by muscle protein synthesis, was higher in fed than in fasting newborn lambs (fig. 2). The leucine flux from whole body protein breakdown was unaffected by nutritional status (table 1). Feeding colostrum stimulated muscle protein synthesis, which was in keeping with body weight gain and protein accretion.

Methods of comparing amino acid composition of proteins: application to undigested proteins in the preruminant calf.

The digestive utilization of dietary proteins at different sites along the digestive tract and the effects of their ingestion on the function of the digestive tract (secretion of endogenous proteins, development of microflora) can be inferred from the proportions of dietary, endogenous or microbial proteins. A first approach was to examine the proportions of some characteristic amino acids. A more accurate interpretation could be made by studying the additional undigested protein provided by the ingestion of an 'experimental' diet whose composition was calculated, for example, with regard to the undigested protein obtained with a very digestible diet (milk in the calf). These interpretations were often insufficient and did not extract all of the possible information. Thus, more global methods with statistical criterions had to be used. Some allowed two proteins (correlation and linear regression, average relative difference, chi 2) to be compared. Others made it possible to take many proteins into consideration (factorial correspondence analysis). Finally, examples were given to seek the respective proportions of many proteins in a complex mixture or to estimate the most probable amino acid composition of the 'microbial + endogenous' proteins which escaped digestion in the small intestine. These various approaches have been discussed, with examples taken from our experimental results obtained in the preruminant calf, to show their advantages and limitations. In any case, the quality of the interpretation depends on the quality of the available results on the amino acid composition of endogenous, microbial and undigested dietary proteins.

[Effect of the kinetics of gastric emptying of food on blood insulin levels in the preruminant calf]. / Influence de la cinétique d'évacuation gastrique de l'aliment sur l'insulinémie chez le veau préruminant.

The aim of this work was to clarify the possible role of blood metabolites (glucose, aminoacids, triglycerides) in the regulation of postprandial blood insulin in the preruminant calf. The animals used were 6 male Friesian bull calves with an average weight of 80 kg. They were divided into groups I and II. During the first experimental period (A), group I received a control diet that contained skim-milk powder as the only protein source, whereas group II received an experimental diet containing fish protein concentrate as the main protein source. During the second experimental period (B), the diets were switched. It was previously shown that the rate of fat and amino acid absorption increased when milk proteins in such milk substitutes were replaced by hydrolyzed fish proteins (Guilloteau et al., 1975). The results showed that during any experimental period in the control group, there was a decrease in the postprandial blood free amino nitrogen. Blood triglycerides exhibited a small increase at 0.5 h after the meal but a large decrease at 1-4.5 h. The meal also resulted in a very large increase in blood glucose with maximal values occurring at 1-4.5 h. Blood insulin showed a large increment at 0.5 h then increased slowly, peaking at 2-3 h. The postprandial increase in blood insulin was less during the first experimental period than during the second one. In calves fed the fish diet, blood free amino nitrogen and blood triglycerides showed a large postprandial increase. Blood glucose exhibited a smaller postprandial increment than in the controls and began to decrease at half an hour. In contrast, the trend of changes in blood insulin was the same as in the controls (i.e. a maximum at 3 h occurring after a large increase at 0.5 h). There were no significant differences in blood insulin between the two experimental periods. It was lower in the calves fed the fish diet than in the controls during the first experimental period; during the second period, it was similar in both groups. From these observations, it may be inferred that, as compared to the control diet, the fish diet resulted in a decrease in glucose stimulation of postprandial insulin secretion; in contrast, the effect of aminoacids and lipids may be increased.