In vivo metabolism of leucine and alpha-ketoisocaproate in the pig: influence of dietary glucose or sucrose.
The influence of dietary glucose (G) and sucrose (S) on leucine metabolism was evaluated in 10 immature pigs. The diets were isoenergetic and isonitrogenous with 40% of energy being derived from G or S. Animals were fed their diets at least 1 wk prior to the study. Each animal was studied by using a continuous infusion of L-[4,5-3H]leucine and [U-14C] alpha-ketoisocaproate (KIC) to permit measurement of the metabolism of leucine. After a meal, the pigs fed the glucose meal had higher mean plasma glucose and insulin concentrations than pigs fed a sucrose-containing meal. Arterial KIC concentration decreased after feeding either meal, but the arterial leucine concentration remained unchanged. In pigs fed sucrose, plasma fructose increased after the meal and was cleared by the hind limb in the same proportion as plasma glucose (11%). The hind limb glucose clearance was 16% in the glucose-fed pigs. Animals fed the glucose meal had three times greater hind limb uptake of leucine than animals fed the sucrose meal. No dietary influence on hind limb metabolism of KIC could be detected from arterial-venous differences. The whole-body leucine-KIC kinetic data suggested that preprandial tissue proteolysis was greater in pigs fed glucose than in those fed sucrose. Postprandial protein synthesis increased (24%) over fasting values only in pigs fed glucose. This was accompanied by a decrease in the percentage of the leucine pool converted to KIC. These observations indicate that both pre- and postprandial aspects of protein metabolism can be influenced by the dietary carbohydrate source.
D000818:Animals; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D005215:Fasting; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D007651:Keto Acids / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism*; D008433:Mathematics; D008954:Models, Biological; D013395:Sucrose / Q000494:pharmacology*; D013552:Swine / Q000378:metabolism*
D004040:Dietary Carbohydrates; D007651:Keto Acids; D013395:Sucrose; C013082:alpha-ketoisocaproic acid; D007930:Leucine; D005947:Glucose