Effect of a Major Gene for Growth on Protein Synthesis in Mice

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Abstract
Rates of protein synthesis of mice with a major gene (hg) for rapid postweaning gain (line Ch) and their normal counterparts (line CH) were determined at 21, 31 and 42 d of age with an intraperitoneal injection of a flooding dose of 14C-leucine. A preliminary experiment demonstrated that the relationship between the specific activities of leucine in acid-soluble supernatants and carcass protein corresponded to the theoretical precursor-product relationship, indicating that the method is valid for estimating protein synthesis rates. Using this method at 21, 31 and 42 d of age, whole-body protein fractional synthesis rates (FSR) were 43.7, 32.7 and 29.1%/d and 41.9, 32.6 and 33.1%/d for lines CH and Ch, respectively. Although differences between lines were not significant, FSR decreased with age. Absolute synthesis rate (ASR), where ASR = (FSR) × (whole body protein), was greater (P<.001) at 21, 31 and 42 d of age in line Ch as compared with CH, and increased (P<.001) with age. The relative contributions of liver, gastrointestinal tract, heart-kidney-lung and remaining carcass to whole body protein ASR were not affected by line, but did change (P<.05) with age. Whole body protein fractional breakdown rate (FBR), calculated as FSR minus whole body protein fractional growth, indicates that differences between lines CH and Ch whole-body FSR and(or) FBR exist only between 24 and 33 d of age, and that the maximum value of this difference probably does not exceed 10%. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science