Postprandial leucine deficiency failed to alter muscle protein synthesis in growing and adult rats

• Published in: Nutrition (Burbank, Los Angeles County, Calif.) Vol. 23; no. 3; pp. 267 - 276
• Main Authors: Debras, Elisabeth, Prod’homme, Magali, Ph.D, Rieu, Isabelle, Ph.D, Balage, Michèle, Ph.D, Dardevet, Dominique, Ph.D, Grizard, Jean, Ph.D
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.03.2007; Elsevier; Elsevier Limited
• Subjects: Aging - metabolism; Amino acids; Animals; Animals, Newborn - growth & development; Biological and medical sciences; Carbon Isotopes; Feeding. Feeding behavior; Food; Fundamental and applied biological sciences. Psychology; Gastroenterology and Hepatology; Insulin; Insulin - blood; Leucine; Leucine - administration & dosage; Leucine - deficiency; Life Sciences; Male; Metabolism; Muscle; Muscle Proteins - biosynthesis; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; Musculoskeletal system; Plasma; Plasma free amino acids; Postprandial; Postprandial Period - physiology; Protein synthesis; Proteins; Random Allocation; Rats; Rats, Wistar; Rodents; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Young adults; Plasma free amino acids; Muscle; Leucine; Protein synthesis; Postprandial; Human; Rat; Deficiency; Rodentia; Striated muscle; Blood plasma; Vertebrata; Mammalia; Aminoacid; Animal; Adult; MUSCLE; POSTPRANDIAL; PROTEIN SYNTHESIS; LEUCINE; PLASMA FREE AMINO ACID
• ISSN: 0899-9007; 1873-1244
• DOI: 10.1016/j.nut.2006.12.003

Abstract Objective This study examined the effect of a specific acute postprandial leucine deficiency on skeletal muscle protein synthesis in growing and adult rats. Because the anabolic action of dietary leucine supplementation is controversial, except during aging, we hypothesized that the maximum leucine effect might be already achieved for a normal postprandial rise of leucine. Preventing this rise during the 1- to 3-h period after feeding may reveal the leucine regulation. Methods On the day of the experiment, rats were fasted (postabsorptive, PA group) or fed for 1 h a control meal (postprandial, control, PP group) or a leucine-poor meal (postprandial, PP-Leu group). Muscle protein synthesis was assessed in vivo, over the 1- to 3-h period after meal distribution, using the flooding dose method (L-1-13 C phenylalanine). Results As expected, the postprandial increase in plasma free leucine was specifically abolished after feeding the leucine-poor meal, whereas all the other plasma free amino acids were roughly at normal postprandial levels. Plasma insulin increased after feeding in young rats but was constant in adult rats. Plasma insulin was similar whatever dietary leucine levels. Rates of muscle protein synthesis were stimulated by feeding in gastrocnemius and soleus muscles from young rats but only in gastrocnemius muscles from adult rats. The PP-Leu group did not differ from the control PP group regarding muscle protein synthesis. Conclusion The rise in plasma free leucine is not required for the stimulation of muscle protein synthesis during the 1- to 3-h period after feeding young and adult rats, as previously observed in old rats.