A Possible Role for Catecholamines in the Ventilatory Responses Associated with Internal Aciosis or External Hypoxia in Rainbow Trout Oncorhynchus Mykiss

Summary Plasma catecholamine levels and gill ventilation were measured in rainbow trout (Oncorhynchus mykiss) during acidosis and hypoxia. There was an increase in both plasma catecholamines and ventilation correlated with the acidosis. Fish exposed to hyperoxia prior to acid infusion did not show significant changes in catecholamines or ventilation. Those treated with the /3-adrenergic antagonist propranolol before acidosis showed increases in catecholamines but not ventilation. Hypoxia was also associated with increases in endogenous catecholamines and ventilation, and the increase in ventilation could be partially blocked with propranolol. This increase in ventilation during hypoxia was not inhibited by a saline injection alone. It is proposed that catecholamines act to modulate ventilatory responses in fish under both acidotic and hypoxic conditions. If a central H + chemoreceptor exists in fish to control breathing, it can be inhibited by hyperoxia or by /3-receptor blockade.