title: Seasonal acclimatization in American goldfinches: the role of the pectoralis muscle.
abstract: The present study attempts to assess whether the marked seasonal changes in the capacity for shivering thermogenesis in American goldfinches (Carduelis tristis) involve adjustments of metabolic pathways of the pectoralis muscles similar to those observed in mammalian muscle in response to endurance training, i.e., changes favoring increased reliance on fatty acid oxidation and decreased utilization of carbohydrate reserves. Analysis of seasonal changes in enzyme profile of the pectoralis muscle revealed that winter-acclimatized birds have significantly greater (P less than 0.05) activities of phosphorylase, phosphofructokinase, and beta-hydroxy-acyl-CoA dehydrogenase than do birds in other seasons. The activities of citrate synthase and hexokinase do not vary seasonally. These results differ fundamentally from the pattern of changes in enzyme activities associated with endurance adaptation in mammals. Furthermore no seasonal changes were observed in capacities for the oxidation of fatty acids (palmitate and linoleate) or pyruvate in either crude homogenates or isolated mitochondria of goldfinch pectoralis muscles. The oxidation of pyruvate by isolated pectoralis muscle mitochondria was inhibited (greater than 90%) by the oxidation of palmitoyl carnitine at palmitoyl carnitine concentrations as low as 50 microM. These data agree with physiological observations indicating little use of glucose by this tissue during steady-state shivering. However, the extent of this inhibition does not vary seasonally. Therefore the present study fails to document any significant seasonal change in the catabolic pathways of the pectoralis muscle that would link observed seasonal changes in capacity for shivering thermogenesis with a shift in the balance of substrate use by this tissue.
mesh_terms: D015094:3-Hydroxyacyl CoA Dehydrogenases / Q000378:metabolism; D000064:Acclimatization; D000818:Animals; D001717:Birds / Q000502:physiology*; D002950:Citrate (si)-Synthase / Q000378:metabolism; D006593:Hexokinase / Q000378:metabolism; D007700:Kinetics; D008931:Mitochondria, Muscle / Q000201:enzymology; D009132:Muscles / Q000502:physiology*; D010101:Oxygen Consumption; D010732:Phosphofructokinase-1 / Q000378:metabolism; D006005:Phosphorylases / Q000378:metabolism; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism; D012621:Seasons; D013385:Succinate Dehydrogenase / Q000378:metabolism
chemical_list: D011768:Pyruvate Dehydrogenase Complex; D015094:3-Hydroxyacyl CoA Dehydrogenases; D013385:Succinate Dehydrogenase; D002950:Citrate (si)-Synthase; D006005:Phosphorylases; D006593:Hexokinase; D010732:Phosphofructokinase-1