Plasma Catecholamines in the Lesser Spotted Dogfish and Rainbow Trout at Rest and During Different Levels of Exercise

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Abstract
The hypothesis that there is an increase in plasma catecholamines during exercise in fish and that they play an important role in the cardiovascular adjustments during exercise was investigated in the lesser spotted dogfish and rainbow trout. In resting fish plasma catecholamines were at a concentration of 10−9–10−8 mol I−1. During spontaneous swimming in the dogfish, adrenaline increased by 3·3 times to l·9× 10−8mol I−1 and noradrenaline increased by 2·3 times to 3·2× 10−8mol I−1. In rainbow trout swimming at a steady 1 body lengths−1 (Ls−1) in a water channel, the levels of both amines decreased to approximately 25% of the resting values. When swimming to apparent exhaustion at approximately 2Ls−1, adrenaline was 10 times the resting value at 1·4× 10−8mol I−1, whereas noradrenaline was 2·2 times the resting value at 2·3 × 10−8mol l−1. Only after repeated burst swimming for 2–3 min did the levels of plasma catecholamines increase substantially above the resting values. In the dogfish, both amines were at 10−7moll−1, whereas in the rainbow trout, noradrenaline was at 8·5× 10−8mol I−1 and adrenaline was at 2× 10−7mol l−1. These levels were compared with the concentrations of catecholamines used by other workers to elicit changes in the branchial vasculature, gas exchange at the gills or gas transport to the tissues. In lesser spotted dogfish, the levels of adrenaline and noradrenaline present in the plasma during spontaneous swimming have 80% and 50% of maximum effect on gill blood vessels, respectively, whereas in rainbow trout the levels present when swimming to apparent exhaustion have approximately 20 % of maximum effect on the branchial vasculature. The levels present in the trout after repeated burst swimming have 40% of maximum effect on blood vessels in the gills. The difference between the dogfish and the trout may be related to the lack of innervation of the gill blood vessels in the former. Enhancement of gas exchange across the gills of rainbow trout can be demonstrated by using adrenaline at the concentration found after repeated burst swimming. It is possible, however, that the concentration of adrenaline found in the plasma of trout after swimming to apparent exhaustion may cause an increase in the concentration of oxygen in arterial blood, thus enhancing oxygen delivery to the tissues. It therefore appears that, in rainbow trout, only the levels of plasma catecholamines attained during repeated burst swimming are likely to have clear effects on oxygen delivery to the tissues. Burst swimming is powered by the white anaerobic muscle fibres, so oxygen delivery during the exercise will not be of value. An elevated supply of oxygen after such exercise could well be important, although it is not certain to what extent a fish would engage in repeated burst swimming for several minutes in its natural environment.