Effect of daily exercise and food intake on leucine oxidation

Oxidation of the branched-chain amino acid leucine was studied in 22 male Sprague-Dawley rats (70–90 g) over 3 days following the ingestion on Day 1 of a mixed diet containing a tracer dose (10 μCi) of l-[1- 14C]Leu. One group (E) completed 1 hr exercise at 80% VO 2 max immediately after a 2-hr feeding period on all 3 days, while a second group served as a control. Rats from group E were sacrificed immediately after the 2 hr feeding on Day 1, following exercise on Days 1 and 3, and at the end of Day 3. The following were determined: (1) continuous 14CO 2 production, (2) radioactivity remaining in the gastrointestinal tract, and (3) distribution of free vs protein bound 14C in muscle and liver. The results indicated that (1) 14CO 2 production increased during exercise on all 3 days ( P < 0.01), (2) 14CO 2 production also increased ( P < 0.05) following food intake (unlabeled diet), (3) 14CO 2 production due to exercise was greater than that due to food intake ( P < 0.05), (4) absolute 14CO 2 production decreased dramatically by 15 hr of Day 1 ( P < 0.01) with little change thereafter (except with exercise and food intake on Days 2 and 3), (5) >98% of the labeled diet was absorbed from the GIT 51 hr postingestion, and (6) 14C in the free pool of muscle and liver could account for