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Journal of Experimental Biology 152,353-367 (1990)
Published by Company of Biologists 1990

Effects of Catecholamines on Gas Exchange and Ventilation in Rainbow Trout (Salmo Gairdneri)

RICHARD C. PLAYLE ¹, R. STEPHEN MUNGER ¹, and CHRIS M. WOOD ¹

¹ Department of Biology, McMaster University, Hamilton, Ontario, Canada L8S 4K1

A transient inhibitory effect of catecholamines on relative CO₂ excretion, mediated by an inhibition of HCO₃^- dehydration through the red blood cell (RBC), has been proposed to cause the increase in Pa_COCO2 routinely observed after strenuous exercise in fish (‘CO₂ retention hypothesis’, Wood and Perry, 1985). To evaluate this idea, trout fitted with arterial cannulae, oral membranes and opercular catheters were placed in ventilation chambers. Pa_COCO2 RBC intracellular pH (pHi) and other blood acid-base parameters were monitored from the arterial cannulae. The ventilation chamber system allowed continuous, almost instantaneous, measurements of water O₂ and CO₂ across the gills, and therefore of respiratory exchange ratio (RE), as well as ammonia, mean expired pH and ventilation volume (Vw). Physiological doses of adrenaline and noradrenaline (3.2nmolkg^-1), designed to duplicate typical post-exercise concentrations, together with appropriate saline controls, were injected into resting fish. Adrenaline caused an immediate hypoventilation, while the response to noradrenaline was biphasic: hyperventilation followed by hypoventilation. With both drugs, O₂ and CO₂ increased, but RE remained constant (adrenaline) or increased (noradrenaline). There was no evidence of a specific inhibition of CO₂ excretion, nor was there any increase in Pa_COCO2; changes in RBC pHi were small (noradrenaline) or non-existent (adrenaline). These results confirm those of Steffensen et al. (1987) and do not support the CO₂ retention hypothesis. However, the RBCs of resting trout may be relatively insensitive to catecholamines at normal arterial blood pH (pHa).

Key words: catecholamines, CO₂ excretion, ventilation, red blood cell pH, respiratory exchange ratio

Accepted on April 19, 1990