P1.160 Wednesday, Jan. 4 Seasonal Phenotypic Flexibility of Muscle Aerobic Enzyme Activities in Small Birds. KING, M.O.*; ZHANG, Y.; TORDSEN, T.; SWANSON, D.L.; University of South Dakota email@example.com
Small birds increase thermogenic capacity during the energetically demanding periods of winter and migration. This increase could be supported by enhanced cellular aerobic capacity and provision of fats as fuel. We examined activities of citrate synthase (CS), beta-hydroxyacyl CoA dehydrogenase (HOAD) and carnitine palmitoyl acyl transferase (CPT) in skeletal muscles and heart in several species of small birds during migration and winter in cold climates to determine if enzyme activities varied with energy demand and thermogenic capacity. Pectoralis and heart CS activity increased in winter black-capped chickadees, but not in winter American goldfinches. Muscle CS activity did not vary significantly with migration for any muscle for any species. Muscle HOAD activity did not vary significantly with season or migration for any muscle or any species. CPT activity increased significantly with migration in some muscles of warbling vireo and yellow warbler, but decreased in heart muscle of yellow-rumped warbler and did not vary significantly in many cases. Muscle CPT activities did not increase with thermogenic capacity in winter birds. The absence of consistent variation in muscular enzyme activities with seasonal variation in energy demand agrees with previous data from small birds and suggests that this is not the principal mechanism generating phenotypically flexible responses of thermogenic capacity to changing energy demands. Future studies will include (1) path analysis of the lipid provision and catabolism pathway, including lipid transporters, to determine if lipids limit aerobic capacity during prolonged exercise and (2) examination of concomitant variation in muscle masses and regulation of seasonal or migration-induced muscle growth.