ESTIMATION OF TOTAL PROTEIN SYNTHESIS, ACCRETION AND DEGRADATION IN RATS

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Abstract
A method of estimating the rates of total protein synthesis, accretion and degradation in rats was investigated. Rats maintained on a continuous feeding regimen were given L-(U-14C) tyrosine and L-(U-14C) phenylalanine either with the diet or by continuous infusion while N consumption and excretion were measured. The percent of administered 14C expired as 14CO2 was used to calculate the rate of phenylalanine hydroxylation as well as the rate of phenylalanine incorporation into body protein according to a two-pool model of phenylalanine and protein metabolism. Finally, the whole body rates of protein synthesis, accretion and degradation in growing rats were calculated. All rats received 12 g of feed per day. Those that were given (14C) amino acids with the diet were growing at a mean rate of 3.0 g/day and had a mean body weight of 160 g. The mean rates of protein synthesis, accretion and degradation for these rats were 1.76, 0.74 and 1.02 g of protein/day, respectively. Rats that were given (14C) amino acids by continuous infusion were growing at a mean rate of 2.9 g/day and had a mean body weight of 123 g. The mean rates of protein synthesis, accretion and degradation in these rats were 1.39, 0.80 and 0.59 g protein/day, respectively.