OLSON, J.M.; WALSH, M.E.; DANG, C.; Villanova Univ., PA; Villanova Univ., PA; Villanova Univ., PA: Ontogenetic Changes in the Thermal Sensitivity of Catabolic Enzymes in Skeletal Muscle of the Japanese quail (Coturnix japonica)

Young birds are susceptible to hypothermia due to incompletely developed thermogenic capabilities and unfavorable S:V ratios and concomitantly high heat loss. The development of endothermy in quail chicks is likely dependent in part on improvement in the catabolic capacity of key skeletal muscles involved in shivering. Because young precocial chicks must still be capable of locomotion and thermoregulation despite hypothermia, catabolic enzymes in both the leg and pectoralis muscles might be less temperature sensitive in young chicks. We examined the ontogenetic changes in the capability of pectoral muscle (PM) and mixed leg muscles (LM) of precocial Japanese quail to generate ATP through the catabolism of glucose in the glycolytic pathway (pyruvate kinase [PK] activity), fatty acids through the beta-oxidative pathway (3-hydroxyacyl-CoA-dehydrogenase [HD] activity), and acetyl-CoA through the TCA cycle (citrate synthase [CS] activity). Muscle samples were collected from adults and 1,2,4,8,12,16, 22,28, and 40 d old chicks, homogenized, and prepared for enzyme assays. Enzyme activities were assessed spectrophotometrically at 25�, 32.5� and 40�C. PM demonstrated significant increases in all three enzymes; PK activity increased significantly between 8d-12d while HD and CS increased later (~30d). LM experienced smaller increases (PK), remained constant or even decreased (CS and HD) during the same period. CS and PK activities in PM were slightly less temperature sensitive in younger chicks than in their older counterparts, but the corresponding comparisons in LM revealed either no significant differences or even a small but significant opposite trend. These data support the conclusion that the PM serves an increasingly important function in both thermoregulation and locomotion.