Estimation of whole body protein synthesis from oxidation of infused [1-14C]leucine.
In rats infused with NaH14CO3, 14CO2 exhalation approached an asymptotic rate equal to 96.0 +/- 1.3 (SD) % 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 16-25% of 14C infusion rate (mean 20.4%) in a monoexponential manner with a half-time of approximately 31 min. Whole body protein synthesis (S) was calculated from 1-F and urea N plus ammonia N excretion (C) as S = CF/(1-F). S was a uniform function of body weight in these rats, in six additional rats in which S was measured 6 h after single intravenous injection of [1-14C]leucine and also in previously reported rats given single injections. The relationship was S (mg.100 g-1.h-1) = 11-0.143 body wt (g) +/- 8.3. In six 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. These results support the validity of the expired 14CO2 technique for measuring S.
Yagi
M
M
Department of Pharmacology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Walser
M
M
D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002245:Carbon Dioxide / Q000032:analysis; D002250:Carbon Radioisotopes; D007262:Infusions, Intravenous; D007700:Kinetics; D007930:Leucine / Q000008:administration & dosage / Q000378:metabolism*; D008297:Male; D010084:Oxidation-Reduction; D014176:Protein Biosynthesis; D011865:Radioisotope Dilution Technique; D051381:Rats; D011919:Rats, Inbred Strains; D012119:Respiration; D012964:Sodium / Q000378:metabolism; D017693:Sodium Bicarbonate; D014508:Urea / Q000378:metabolism
D001639:Bicarbonates; D002250:Carbon Radioisotopes; D002245:Carbon Dioxide; D000641:Ammonia; D017693:Sodium Bicarbonate; D014508:Urea; D012964:Sodium; D007930:Leucine