High-altitude acclimation increases the triacylglycerol/fatty acid cycle at rest and during exercise

High-altitude acclimation alters lipid metabolism during exercise, but it i s unknown whether this involves changes in rates of lipolysis or reesterifi cation, which form the triacylglycerol/fatty acid (TAG/FA) cycle. We combin ed indirect calorimetry with [2-H-3]glycerol and [1-C-14]palmitate infusion s to simultaneously measure total lipid oxidation, lipolysis, and rate of a ppearance (R-a) of non-esterified fatty acids (NEFA) in high-altitude-accli mated (HA) rats exercising at 60% maximal O-2 uptake ((V) over dotO(2 max)) During exercise, relative total lipid oxidation (%(V) over dotO(2)) equale d sea-level control (SL) values; however, acclimation greatly stimulated li polysis (+ 75%) but had no effect on R-a NEFA. As a result, TAG/FA cycling increased (+ 119%), due solely to an increase in recycling (+ 144%) within adipocytes. There was no change in either group in these variables with the transition from rest to exercise. We conclude that, in HA, 1) acclimation is a potent stimulator of lipolysis; 2) rats do not modify TAG/FA cycling w ith the transition to exercise, and 3) in normoxia, HA and SL derive the sa me fraction of their total energy from lipids and carbohydrates.