Propranolol Impairs the Hyperventilatory Response to Acute Hypercapnia in Rainbow Trout Available to Purchase

This study investigated the possible role of catecholamines in the ventilatory response of rainbow trout (Oncorhynchus mykiss) to acute external hypercapnia. The ventilatory response to hypercapnia [partial pressure of CO₂ in water of fish pre-treated with the selective β-adrenoceptor antagonist, D,L-propranolol, was compared with that of D-propranolol (an isomer with minimal β-antagonistic activity) and saline pre-treated fish (sham). A sustained 3.6-fold increase in gill ventilation volume was observed in the sham and D-propranolol-treated groups during the 30min interval of hypercapnia. Fish pre-treated with D,L-propranolol displayed a blunted hyperventilatory response to hypercapnia (1.9-fold increase at 30min). These results indicate that the β-component of an adrenergic response is involved in the usual hyperventilatory response to external hypercapnia. It is suggested that the impaired hyperventilatory response of the D,L-propranolol-treated group reflects an inhibition of central adrenergic mechanism(s) involved in the hyperventilatory reflex to respiratory acidosis.