1. Branched-chain amino acid aminotransferase (EC 2.6.1.42; BCAAT) and branched-chain alpha-keto acid dehydrogenase (EC 1.2.4.4; BCKDH) activities were measured preruminant lamb liver, longissimus dorsi muscle, kidney, jejunum and adipose tissue, 2 h after a meal with or without an excess of leucine. 2. Skeletal muscle contained about 70% of the total basal BCAAT activities of the tissues studied whereas liver contained about 60% of the total BCKDH activities of these tissues. 3. BCAAT activities were very low in preruminant lamb tissues. BCKDH was more phosphorylated in tissues of preruminant lambs than in rats, especially in liver. These low catalytic potentialities might contribute to a low rate of branched-chain amino acid catabolism in sheep. 4. Ingestion of an excess of leucine led to an increase in liver and jejunum BCAAT activities and activation of BCKDH in jejunum.

These studies were undertaken to determine to what extent constant infusion measurements and plasma sampling could provide sensible answers for rates of whole body protein turnover and also which amino acid would be the most representative probe of whole body protein turnover. Whole body protein synthesis rates were estimated in 70-g rats with L-[U-14C]threonine, L-[U-14C]lysine, L-[U-14C]tyrosine, L-[U-14C]phenylalanine, and L-[1-14C]leucine by either simultaneous tracer infusion of four amino acids or by injections of large quantities of 14C-labeled amino acids. In the infusion experiment, indirect estimates of whole body protein turnover based on free amino acid specific radioactivity and stochastic modeling were compared with direct measurement of the incorporation of the tracer into proteins. These two methods of analysis provided similar results for each amino acid, although in each case fractional synthesis rates were lower (by between 26 and 63%) when calculations were based on plasma rather than tissue specific radioactivity. With the flooding-dose method, whole body fractional protein synthesis rates were 41.4, 25.6, 31.1, and 31.4% with threonine, lysine, phenylalanine, and leucine, respectively. These values were similar to those obtained by the continuous infusion method using tissue specific radioactivity for threonine and lysine. For leucine, however, the flooding-dose method provided an intermediate value between the two estimates derived either from the plasma or the tissue specific radioactivity in the infusion method.(ABSTRACT TRUNCATED AT 250 WORDS)

(fig. 1). The apparent digestibility of each diet decreased when that diet was infused into the duodenum at the gastric emptying rate of its protein (slow infusion of the control diet, quick infusion of the fish diet) (table 2) ; infusion at a higher rate (quick infusion of the control diet) increased this effect, while infusion at a lower rate (slow infusion of the fish diet) suppressed it. This decrease in apparent digestibility was more marked for lipid and minerals than for protein.The slow infusion of the fish diet had little effect on faecal amino acid composition (table 4). On the other hand, rapid infusion of the control diet seemed to cause a decrease in the relative proportion of microbial protein in favour of some milk protein fractions (serine and glutamic acid-rich phosphopeptides of 1X' 1' ag 2 and caseins).Blood free amino acid levels, measured during simulation of the gastric emptying of each diet, were similar to those observed during ingestion (table 5). These levels were higher when both diets were infused quickly than when they were infused slowly.In conclusion, the digestion of protein, and especially that of lipid and minerals, as well as the metabolic utilization of amino acids, is highly influenced by the time spent in the abomasum and by the rate of arrival in the duodenum.Introduction.

Summary. Effect of gastric emptying on plasma insulin in the preruminant calf.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 li. During the first experimental period (A), group I received a control diet that contained skim-milk powder as the only protein source, whereas group 11 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.Le remplacement des protéines du lait par des protéines de poisson dans l'aliment d'allaitement distribué au veau préruminant entraîne une accélération de l'évacuation gastrique des lipides, des protéines et parfois du lactose (Guilloteau

L'expérience réalisée avait pour objet de préciser dans quelle mesure l'insuline pouvait modifier l'utilisation de l'azote et de l'énergie chez le Rat en croissance, nourri en 6 repas égaux par jour et soumis à une restriction purement énergétique. Dans ce but, des rats mâles de souche « Wistar n pesant 90 g ont été répartis en 3 lots : un lot A témoin recevant un régime équilibré à base de farine de hareng de Norvège (à 11 , 7 p. 100 de matières azotées) et deux lots B et C recevant un régime riche en protéines (à 19 ,6 p. 100 de matières azotées). Pour une consommation limitée à 6 0 p. 100 de celle des animaux du lot témoin, les animaux des lots B et C ingèrent autant de protéines, de vitamines, de minéraux, mais seulement 6 0 p. 100 de l'énergie. Les animaux du lot C reçoivent journellement 0 , 5 à 1 UI d'insuline, en injection sous-cutanée. La composition corporelle et les teneurs en acides aminés libres du sang, du foie et du muscle sont déterminées sur chaque lot, à l'abattage, lorsque les animaux ont atteint un poids moyen de I50 g. La restriction énergétique ralentit la croissance (57 p. ioo), diminue l'efficacité alimentaire apparente de l'azote et de l'énergie et l'adiposité du corps des animaux. Le traitement de ces animaux par l'insuline améliore la croissance, les rétentions azotées et énergétiques mais ne modifie pas la composition corporelle. La restriction énergétique s'accompagne d'une diminution presque générale des teneurs en acides aminés libres non indispensables et d'une accumulation de la thréonine libre dans le sang, le foie et le muscle ; les teneurs de la plupart des acides aminés libres indispensables augmentent légèrement dans le muscle et diminuent dans le foie. Par rapport aux animaux dont l'alimentation énergétique est limitée, le traitement par l'insuline accentue la baisse des teneurs en acides aminés libres non indispensables dans le sang et le muscle, diminue les teneurs de la plupart des acides aminés libres indispensables dans le muscle et augmente les teneurs de la plupart de ces derniers dans le foie.