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Journal of Experimental Biology 147,471-491 (1989)
Published by Company of Biologists 1989

The Role of -Adrenoreceptors in the Recovery from Exhaustive Exercise of Freshwater-Adapted Rainbow Trout

D. G. MCDONALD ¹, Y. TANG ², and R. G. BOUTILIER ²

¹ Aquatron Laboratory, Department of Biology, Dalhousie University Halifax, Nova Scotia, Canada, B3H 4J1; Department of Biology, McMaster University, 1280 Main St West, Hamilton, Ontario, Canada, L8S 4K1
² Aquatron Laboratory, Department of Biology, Dalhousie University Halifax, Nova Scotia, Canada, B3H 4J1

Rainbow trout, fitted with arterial catheters, were exercised to exhaustion by manual chasing and then injected with either saline (controls), the -agonist isoproterenol or the -antagonist propranolol. Blood acid-base status, branchial unidirectional and net fluxes of Na⁺ and Cl^-, and net fluxes of ammonia and acidic equivalents (J^H_net) were monitored over the subsequent 4 h of recovery. These same parameters were also monitored in normoxic, resting fish following isoproterenol injection and in exercised fish following acute post-exercise elevation of external NaCl concentration. In addition to confirming an important role for -adrenoreceptors in the regulation of branchial gas exchange and red cell oxygenation and acid-base status, we find a significant -adrenergic involvement in the flux of lactic acid from muscle and in J^H_net across the gills. Both isoproterenol infusion (into nonexercised fish) and exhaustive exercise were found to cause net acid excretion. The post-exercise J^H_net was further augmented by elevating [NaCl] but was not affected, in this instance, either by -stimulation or blockade, indicating that J^H_net was not entirely regulated by a -adrenergic mechanism. On the basis of a detailed analysis of unidirectional Na⁺ and Cl^- fluxes, we conclude that the increase in J^H_net following exercise arose mainly from increased Na⁺/H⁺(NH₄⁺) exchange and that the upper limit on J^H_net was set by the supply of external counterions and by the increase in branchial ionic permeability that invariably accompanies exhaustive exercise.

Key words: catecholamines, rainbow trout, exercise, gills, acid-base regulation

Accepted on July 3, 1989

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