LACTATE METABOLISM IN RAINBOW-TROUT

We have investigated the metabolic fate of blood lactate in resting ra inbow trout and in fish recovering from a bout of exhaustive exercise. At rest and during recovery from exercise, the majority of blood lact ate was oxidized, the proportion increasing with increasing oxygen con sumption. It is estimated that, during recovery from exhaustive exerci se, lactate released from the muscle has the potential to fuel a signi ficant portion of oxidative metabolism. The bulk of the remaining bloo d lactate reappeared in the muscle lactate pool, probably via direct u ptake by the muscle. There was a significant incorporation of blood la ctate into the muscle glycogen pool, providing strong evidence for in situ glycogenesis as the mode for muscle glycogen replenishment. To in vestigate the role of the liver in blood lactate clearance, trout were functionally hepatectomized by ligation of the hepatic portal circula tion. The exercise performance of hepatectomized fish was equal to tha t of sham-operated fish and controls, indicating that muscle relies pr imarily on endogenous fuel stores. Furthermore, blood lactate levels i mmediately after exercise were greater and muscle metabolic recovery w as faster in hepatectomized fish than in sham-operated fish and contro ls. These observations suggest that glycogen resynthesis in trout musc le may be retarded because of a non-recoverable loss of substrate (i.e . lactate) from the muscle, because the lactate released is utilized b y the liver. These results are discussed in view of what is known abou t these processes in other ectothermic vertebrates.