MUSCLE AMINO-ACID PATTERN IN OBESE RATS

OBJECTIVE: To determine how the ability of skeletal muscle to manage a mino acids is conditioned by obesity. The test was performed in two di fferent models of obese rats: diet-obese rats and genetically obese ra ts. SUBJECTS: Lean and genetically obese (fa/fa) male Zucker rats were used. DESIGN: For up to 60 d of life lean animals were fed with stand ard chow pellet or with a hypercaloric cafeteria diet. Genetically obe se rats were fed with standard chow pellet during the same period. MEA SUREMENTS: Amino acid concentration in the femoral artery and vein and leg blood flow were measured. Free amino acid concentration. protein and nitrogen content and enzyme activities were determined in whole le g muscle. RESULTS: Amino acid availability was increased in diet-obese animals and remained unchanged in the genetically obese group. The ge netically obese groups had a lower protein content and unchanged conce ntration of amino acids in leg muscle. Furthermore, total nitrogen rem ained unchanged in these animals and they showed an increased activity in alanine aminotransferase and glutamine synthetase. The leg muscle of the diet-obese rats took up several amino acids (Ale, Arg and Val) or released others (mainly Gin and Gly). Conversely, genetically obese rats took up many amino acids and did not release any. CONCLUSIONS: W e conclude that in nutritionally obese rats there is an increased avai lability of amino acids in skeletal muscle. This augmented availabilit y propitiates the increase in the uptake of many amino acids. In genet ically obese rats, the lack of variation in amino acid availability po ints to a possible hereditary alteration that increases the capacity o f different amino acid transport systems. Furthermore. the diminished protein content of fa/fa muscle is not due to a lower availability and intracellular pool of amino acids.