EFFECT OF SUSTAINED HYPERADRENALINEMIA ON EXERCISE PERFORMANCE AND LACTATE THRESHOLD IN RATS

The effect of prolonged elevation of blood adrenaline concentration (s ustained up to 60 h) on exercise performance and lactate threshold (TL A) was investigated in 24 rats on the basis of a incremental, multista ge treadmill exercise test, performed before and after subcutaneous im plantation of retard adrenaline tablets (15 mg), which release adrenal ine at a constant rate of approx. 1.6 mu g min(-1). Blood samples for lactate (LA) determinations were taken from the rats' tails after each exercise stage. The results obtained indicate that hyperadrenalinemia within the physiologic range, sustained for 6 or 12 h, decreases exer cise performance, measured as the maximal speed of running, increases blood LA concentration during submaximal and maximal exercise, and shi fts TLA toward lower exercise intensities than in control or sham oper ated rats. When adrenaline excess was maintained for 60 h the maximal running speed was still reduced, and exercise blood LA was even higher than during earlier stages of hyperadrenalinemia, but TLA returned to control values. In the rat, a moderate excess of circulating adrenali ne, sustained up to 60 h, reduces maximal exercise performance, and ca uses marked elevations in submaximal and maximal blood lactate concent ration. However, this is accompanied by lowering of TLA only in the ea rly stages of hyperadrenalinemia (6 and 12 h), which suggests that shi fts of TLA may occur independently of absolute levels of blood lactate during graded exercise.