The relationship between weight gain and free amino acid concentration of plasma and liver in rats fed a diet supplemented with various amounts of lysine.

Abstract

This study was conducted to determine the effect of feeding graded levels of dietary lysine on weight gain and free amino acid concentra-tions in blood plasma and liver of weanling rats. Animals were fed on diets containing 11.6% wheat gluten (equivalent in nitrogen to a 10% casein diet) supplemented with graded levels of L-lysine HCl (0 to 10%) for 14 days. An outline of the results obtained follows: 1) Maximum weight gain was observed with the groups fed the lysine supplement in the 0.64 to 1.8% range. Growth declined with further in-crease of dietary lysine. 2) Blood and liver were sampled after decapitation 6 hr after the final feeding on the 14th day, and amino acid concentrations were determined. Plasma lysine concentrations rose rapidly as dietary lysine increased and reached the maximum level with the 1.8% lysine supplementation. With the large supplement diet, the lysine con-centrations maintained a plateau. Plasma threonine levels were high when dietary lysine was low. 3) Similar responses of lysine and threonine concentrations in liver to the increase of dietary lysine was also observed, but the effect was markedly less than those of plasma. Most other amino acids in plasma and liver were nearly unchanged even when the dietary lysine was varied over a wide range.