Effect of exercise on the plasma nonesterified fatty acid composition of dogs and goats: Species with different aerobic capacities and diets

The goals of this study were to determine: (i) whether mammals mobilize particular nonesterified fatty acids (NEFA) preferentially during locomotion, (ii) if differences in aerobic capacity or diet can affect the pattern of NEFA mobilization and (iii) which individual NEFA are most representative of total NEFA concentration changes, to use them as tracers for turnover studies. Individual NEFA were measured in trained dogs and goats (VO₂max dog/VO₂max goat=2.2; where VO₂max=max-imal oxygen consumption) during treadmill exercise at 40 and 60% VO₂max. Important interspecies differences in individual NEFA concentrations could be attributed to differences in aerobic capacity. The more aerobic species (dog) had much higher plasma NEFA concentrations for all but one NEFA (18∶0), when compared with the low-aerobic species (goat). In addition, exercise caused a large increase in concentration of individual NEFA in the dogs, with the largest increases seen in 18∶1 (150% above resting values) and 16∶0 (60% increase), but it had no effect in goats. Therefore, the aerobic species has a much higher ability for mobilizing and transporting NEFA in plasma than its low-aerobic counterpart. Two NEFA accounted for more than half total plasma NEFA in both species, 18∶1 (about 35% total NEFA) and 16∶0 (20%). Calculation of variability in percent composition reveals that oleate and palmitate also closely reflect changes in total NEFA and are therefore the most appropriate tracers forin vivo kinetic studies in exercising mammals. Differences in diet and digestion physiology explained some differences in the plasma NEFA composition of the two species; this was reflected in the percent contributions of individual fatty acids to total NEFA: in dogs 18∶1>16∶0>18∶2>18∶0, while in goats 18∶1>16∶0>18∶0>18∶2. Also, only goats had 18∶3 (6% total NEFA), a fatty acid of plant origin, while only dogs had 16∶1 (7% total NEFA). Overall, however, the plasma NEFA composition of goats did not exactly reflect that of their diet due to preabsorptive modification of unsaturated fatty acids, while in dogs there was a good correlation between dietary and plasma NEFA.