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In Vivo Metabolism of Leucine and -Ketoisocaproate in the Pig: Influence of Dietary Glucose or Sucrose^1,2,3,

Department of Animal Science, Iowa State University, Ames, IA 50011

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]-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.

KEY WORDS: • protein metabolism • glucose • sucrose • leucine • -ketoisocaproate • swine

¹ Journal Paper No. J-11848 of the Iowa Agric. and Home Econ. Exp. Stat., Ames. Project No. 2639.

² Supported in part by the National Institutes of Health Grant AM-32540.

³ Presented in part at the 68th annual meeting of the Federation of American Societies for Experimental Biology, St. Louis, MO, April 1984. Helland, S. J., Trenkle, A., Ewan, R. C. & Nissen, S. (1984) Effects of dietary glucose and sucrose on whole body and hind-limb metabolism of leucine and -ketoisocaproate in vivo. Fed. Proc. 43, 463.

Manuscript received 18 July 1985. Revision accepted 15 May 1986.