Muscle glycogen, lactate and glycerol-3-phosphate concentrations of larvaland young adult lampreys in response to exercise

When stimulated, the ammocoetes (larvae) of Geotria australis swim continuo usly at a moderate rate for only approximately 20 min, whereas the downstre am migrants (young adults) of this species did not become exhausted followi ng similar swimming activity over the same period. Mean concentrations of m uscle glycogen in ammocoetes declined during exercise, but returned to rest ing levels within 30 min of recovery, whereas those in young adults changed little during the corresponding periods. Moreover, muscle lactate concentr ations of ammocoetes rose markedly during exercise and the first 30 min of recovery, before declining significantly, while those of young adults remai ned similar during and immediately after exercise. Calculations, using the glycogen and lactate concentrations immediately after exercise, suggest tha t during exercise glycogen is, to some extent, utilised anaerobically (appr ox. 24%) by ammocoetes, but only aerobically by young adults. Furthermore, since young adults used only a small amount of glycogen, they presumably me tabolised triacylglycerol aerobically to produce energy. Muscle glycerol-3- phosphate levels were far higher prior to and immediately after exercise in downstream migrants than in ammocoetes and then declined precipitously. Th e above trends in muscle glycogen and lactate of larval G. australis parall els, to some degree, those recorded by other workers for upstream migrant P etromyzon marinus that had been exercised to exhaustion. (C) 2001 Elsevier Science Inc. All rights reserved.