In vivo ¹⁴C Isotopic Evaluation of Amino Acid Oxidative Catabolism in the Growing Chick

Abstract

A single dose of [1–¹⁴C] or [U-¹⁴C]glycine or L-[1–¹⁴C] or [U-¹⁴C]valine was injected intraperitoneally into 1- and 3-week-old chicks. Continuous automatic determination of respiratory ¹⁴CO₂ and determination of ¹⁴C in excreta and uric acid were carried out for 8 h. Computer-aided analysis of the kinetics of respiratory ¹⁴CO₂ demonstrated two exponentially decreasing components, ‘fast ¹⁴CO₂’ and ‘slow ¹⁴CO₂’. Fast ¹⁴CO₂production represents the immediate oxidation and/or decarboxylation of the ¹⁴C-labeled amino acid. The half-lives differed according to the nature of the 14C-labeled amino acid but not to the age of the chick. The size of the acetyl-CoA pool labeled by [¹⁴C]glycine was between 10 and 15 mmol/l00 g of chick. Metabolic partition of a circulating plasma free amino acid between oxidation and retention could be quantified by an isotopic index.

In vivo ¹⁴C Isotopic Evaluation of Amino Acid Oxidative Catabolism in the Growing Chick

“…The experimental results obtained with the 34 ani mals used in the investigations reported in the preced ing paper [Simonnet et al, 1989] were considered. Four additional experiments were performed: (1) five 2-week-old chicks were injected intraperitoneally with 0.74 MBq of /,-[l-l4C]methionine (specific ac tivity 1.85 MBq/pmol, radiopurety 98%; CEN Saclay); (2) four 3-week-old chicks were injected simul taneously with, respectively, [U-l4C]glycine (2 chicks) or valine (2 chicks) and 100 pg of cycloheximide per 100 g of animal; (3) inhibition of protein synthesis by cycloheximide was determined in the plasma and tis sues of a 3-week-old chick injected with [U-l4C]valine [Ng, 1988], and (4) two 2-week-old chicks were simul Values are means ± SEM.…”

“…The investigation procedures, intraperitoneal in jection of the labeled molecules and radioactivity measurements, determination of the exponentially decreasing components, have been described in the preceding study [Simonnet et al, 1989], Results Table 1 gives the computer-calculated half-life values of the respiratory slow 14C02 component. Investigation with methionine gave a half-life of 180 min (SEM 15.7) not significantly different from the values ob tained with glycine and valine, i.e.…”

“…Slow 14C 0 2 showed an exponential decrease of its specific radioactivity [Simonnet et al, 1989]. The origin of slow 14C 0 2 should be determined in relation with cellular amino acid catabolism and protein renewal.…”