Effect of fasting on glucose and palmitate metabolism of perfused rat heart

The metabolism of glucose U-C 14 , 5 mm, and palmitate 1-C 14 , 0.75 mm (complexed to 0.5% albumin), was studied in isolated perfused hearts taken from three groups of rats: fed ad libitum, fasted overnight, or fasted 4 days. The changes in glucose metabolism associated with fasting were: decreased glucose uptake, decreased C 14 O 2 formation, decreased lactate/pyruvate ratio, and decreased incorporation of glucose carbon into glycogen. In contrast, the uptake of palmitate and incorporation of label into C 14 O 2 and tissue fatty acids were similar in the three groups. When the perfusate contained both glucose and palmitate, glucose oxidation was reduced in both fed and fasted states, but palmitate oxidation was virtually unaltered. It is concluded that the nutritional state of the donor rat markedly affects glucose but not palmitate metabolism of the isolated rat heart, and that palmitate is preferentially oxidized in both fed and fasted states. The possible mechanisms involved are discussed.