To examine the effect of administration of peptides on protein synthsis and breakdown in skeletal muscle and liver after strenuous exercise, male ICR mice were orally administered four kinds of test solutions, containing either 10% (w/v) peptides, protein or amino acids, immediatey after a 3 hour- period of treadmill running. The fractional rate of protein synthesis (Ks) in skeletal muscle and liver was measured using a flooding dose of [³H] phenylalanine. The rate of plasma albumin synthesis was estimated by intraperitoneally injecting a tracer dose of [¹⁴C] leucine and measuring the [¹⁴C] radioactivity incorporated into plasam albumin. The Ks in skeletal muscle was essentially the same in mice administered any of the four kinds of test solutions. The Ks in liver for the peptides, protein and amino acids administered was significantly higher than that for water. However, there was no difference in Ks in liver between the peptides, protein and amino acids. Plasma levels of 3-methylhistidine were significantly higher in mice administered water than in those given the other test solutions. The rate of plasma albumin synthesis was higher in mice administered peptides than in those given the protein or amino acid solutions. These results suggest that a supply of protein after prolonged exercise enhances protein synthesis in the liver and inhibits protein breakdown in skeletal muscle. Moreover, peptides, which are a more readily digestible and more readily absorbable nitrogen source than protein or amino acids, more effectively enhance liver protein synthesis than administered protein or amino acids.

DESCENTE SPORTS SCIENCE Vol.19/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE