Response of enzyme activities and metabolic intermediate concentrations to a long burst of exercise and following resting in muscle and the hepatopancreas of carp

Abstract

The responses of enzyme activities and metabolic intermediate concentrations to a long burst of exercise and following resting were examined in muscle and the hepatopancreas of carp Cyprinus carpio. A 15 min burst of exercise made the fish so exhausted that they could not swim any more. In muscle, the exercise decreased glycogen content significantly and increased lactate content significantly, resulting in a lowered pH. Furthermore, the burst of exercise decreased phosphofructokinase (PFK) activity significantly, although it changed adenosine-5′-monophosphate, adenosine-5′-diphosphate, adenosine-5′-triphosphate, fructose-6-phosphate and citrate concentrations within ranges that could activate PFK. In the hepatopancreas, the exercise increased glucose6-phosphatase and fructose-1,6-bis-phosphatase activities, and glucose and lactate concentrations in the serum, and it decreased glycogen content. Even at 3 h resting after the burst of exercise, the fish had not completely restored many parameters. These results suggest that although the fish tried to enhance in vivo muscular glycolysis through the activation of PFK by changes in metabolic intermediate concentrations, glycolysis seemed to decrease markedly through the inhibition of PFK as a result of the lowered pH. However, the hepatopancreas made a contribution to muscular exercise through glucose supplementation by enhanced gluconeogenesis and glycogenolysis, indicating the presence of an interdependence of carbohydrate metabolism between muscle and the hepatopancreas in the fish.