Influence of low temperature acclimation on fate of metabolic fuels in rainbow trout (Oncorhynchus mykiss) hearts

Abstract

Rainbow trout (Oncorhynchus mykiss) were acclimated to 5 and 20 °C. Oxygen consumption of isolated perfused hearts was measured at 5 or 15 °C with either glucose or palmitate as the exogenous fuel source. With glucose as the fuel there was no significant difference in oxygen consumption of hearts from either acclimation group at either temperature. With palmitate as the fuel source, hearts from fish acclimated to and tested at 5 °C had significantly higher oxygen consumption than hearts from fish acclimated to 20 °C and tested at either 5 or 15 °C. Hearts from fish both acclimated to and tested at 5 °C had a higher oxygen consumption with palmitate than when glucose was supplied. This reflects the preference for fatty acid fuels found in cold acclimated muscle tissue, and consequently the amount of oxygen required to utilize fats. Under all experimental conditions, ¹⁴CO₂ production from either (6-¹⁴C)glucose or (1-¹⁴C)palmitate could account for less than 0.5% of oxygen consumption. Tissue chemical analysis showed that most of the label from (6-¹⁴C)glucose appeared in acid-soluble (glycolytic intermediates, citric acid cycle intermediates, amino acids, etc.) and lipid fractions while most of the label from (1-¹⁴C)palmitate appeared in lipid- or acid-soluble or acid precipitate (protein material) fractions. This indicates considerable dilution of exogenous fuels in endogenous pools, which could account for the discrepancy in measured O₂ consumption and ¹⁴CO₂ production. Glucose catabolism was little affected by either acute or chronic changes in temperature other than an increase in glucose incorporation into the glycogen pool. Hearts from fish both acclimated to and tested at 5 °C showed an increased handling of exogenous fatty acids as reflected by elevated rates of catabolism and incorporation into intracellular lipids.