Octanoate and Nonaoate Oxidation Increases 50―80% Over the First Two Days of Life in Piglet Triceps Brachii and Gracilis Muscle Strips

An in vitro muscle strip incubation system was developed to measure the rate of catabolism of 1 mmol/L [1-(14)C]octanoate, 1 mmol/L [1-(14)C]nonanoate, 1 mmol/L [9-(14)C]nonanoate, and 10 mmol/L [U-(14)C]glucose by measuring the recovery of (14)CO(2). Muscle strips (13 mm × 1.5 mm, ~50 mg) were isolated from triceps brachii and gracilis muscles of newborn and 2-d-old, small (1450 g) piglets. The position of the (14)C label in the substrate affected the rate and amount of recovery in (14)CO(2). Therefore, comparisons were made between age groups (0 vs. 2 d old) within substrates but limited across substrates to comparisons of [1-(14)C]-labeled fatty acids. The medium-chain fatty acid (MCFA) oxidation rates [pmol/(h · mg)] in muscle strips isolated from piglets from the 2 weight groups (1450 g) did not differ (P > 0.99), there was a trend towards a difference between triceps brachii and gracilis muscle (P = 0.09; data not shown), and there were no significant interactions involving pig weight or muscle type; therefore, results were pooled across these factors. During the first 2 d of life, MCFA oxidation [pmol/(h • · mg muscle strip)] increased (P < 0.05) 50-80%, but the glucose oxidation rate did not change (P > 0.82). By d 2, the oxidation rate of nonanoate as represented by the one carbon was 25% greater than for octanoate (P < 0.05). The conversion of [9-(14)C]nonanoate to (14)CO(2) indicated that muscle had the capacity to oxidize the propionyl-CoA produced by β-oxidation of nonanoate and that odd-chain C-9 MCFA provided anabolic carbon to the citric acid cycle.