Estimation of whole body protein synthesis from oxidation of infused [1-14C]leucine
Yagi, M.; Walser, M.
American Journal of Physiology 258(1 Pt 1): E151-E157
1990
ISSN/ISBN: 0002-9513 PMID: 2154116 Document Number: 353818
In rats infused with NaH14CO3, 14CO2 exhalation approached an asymptotic rate equal to 96.0 +or- 1.3 (s.d.) % of the infusion rate of 14C in a monoexponential manner with a half-time of 20 min. In rats infused with [1-14C]leucine, 14CO2 exhalation (/0.96) approached an asymptotic value, (1 - F), of 16 to 25% of 14C infusion rate (mean 20.4%) in a monoexponential manner with a half-time of about 31 min. Whole body protein synthesis (S) was calculated from 1 - F and urea nitrogen plus ammonia N excretion (C) as S = CF/(1 - F). S was a uniform function of body weight in these rats, in 6 additional rats in which S was estimated 6 h after single intravenous injection of [1-14C]leucine and also in previously reported rats given single injections. The relation was S (mg/100 g h) = 110 - 0.143 body weight (g) +or- 8.3. In 6 of these rats, S was also estimated from the plateau specific activity of plasma leucine or plasma 2-ketoisocaproate (KIC); the former estimate of S was significantly lower (by an average of 17%), but S was the same when specific activity of KIC was employed. The results support the validity of the expired 14CO2 technique for estimating S.