Metabolic responses of striped bass (Morone saxatilis) to temperature acclimation. I. Alterations in carbon sources for hepatic energy metabolism

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Abstract
The relative contribution of carbohydrate and lipid to energy metabolism in liver tissue of temperature-acclimated striped bass was examined in vitro. Respirometry experiments were conducted to assess the role of various endogenous foodstuffs in providing reduced two-carbon fragments for aerobic metabolism. Liver composition was measured as a reflection of foodstuff flux and storage. Catabolism of 14C-labeled substrates to 14CO2 was monitored to estimate the tissue capacity for utilization of various classes of compounds. When measured at the temperature of acclimation, oxygen uptake (V̇O2 by liver slices shows near perfect compensation between 15 and 25° C, whereas a 2.75-fold increase is found between 5 and 15°C. Respiratory quotients (R.Q.) near unity are found at 5° C and decrease to 0.85 and 0.82 at 15 and 25° C, respectively. Inhibition of V̇O2 by iodoacetic acid, a glycolytic inhibitor, is near 60% at 5° C and decreases to 30–40% at 15 and 25° C. Evolution of 14CO2 from 14C-labeled glucoses and palmitate confirms a conservation of liver tissue capacity for carbohydrate utilization between acclimation temperatures of 5 and 15° C, and an increasing capacity for utilization of fatty acids as temperature increases. Ratios of 14CO2 from 14C-6-and 14C-1-labeled glucoses indicate a relative increase in the participation of the pentose shunt in carbohydrate metabolism with cold acclimation. The results are consistent with an increasing reliance on carbohydrates for energy metabolism in the cold, whereas lipid substrates are utilized more at warm temperatures. These changes may be adaptive in partitioning energy reserves for seasonal activities of migration and reproduction.