[Characterization of radioactivity distribution in the organism during constant intravenous infusion of tracer amino acids and calculation of the rate of tissue protein synthesis in rats].

Male wistar rats (100 g live mass) were given infusions into the tail vein of 14C-leucine and 14C-lysine simultaneously for 0.5; 1.0; 2.0; 3.0; 4.5; 6.0 and 7.0 hours. At the end of the infusion the specific radioactivity of the free leucine and lysine in the blood plasma, liver, M. gastrocnemius, small intestines and colon were ascertained as well as after the 6-and-7-hour infusion that of the protein-bound leucine and lysine. In all tested tissues the specific radioactivity of the free amino acids attained a plateau during the 6-and-7-hour infusion. The rate constants for the increase were calculated for each organ tested. The two amino acids used are suitable for the calculation of the fractional rate of protein synthesis in tissues. The values of the fractional rate of protein synthesis calculated on the basis of the 6-and-7-hour infusion were: 54 +/- 7.7%/day for the liver, 9.4 +/- 1.2%/day for muscles, 89 +/- 12.2%/day for the small intestines and 42 +/- 5.9%/day for the colon. The simultaneous application of two tracer amino acids is recommendable for the estimation of the precursor pool for protein synthesis and the more accurate calculation of the rate of protein synthesis.