The role of circulating catecholamines in the regulation of breathing in teleosts.

This thesis attempts to elucidate the role of epinephrine and/or norepinephrine in the regulation of ventilation in teleosts while also considering the effects of other potential ventilatory modulators. The ventilatory responses to various external respiratory challenges were quantified and compared with those in fish pre-treated with adrenoceptor antagonists. The effects of experimental elevation of circulating catecholamines on gill ventilation volume (Vw) were assessed. During hypoxia, pre-treatment of fish with either $\alpha$- or $\beta$-adrenoceptor antagonists did not affect the ventilatory response of rainbow trout (Oncorhyncus mykiss) or Atlantic cod (Gadus morhua), regardless of the degree of hypoxia used and the corresponding effects on circulating catecholamine levels. Furthermore, since increases in Vw were observed under mild hypoxia or hypercapnia it is concluded that elevation of circulating catecholamines is not a prerequisite for hyperventilatory responses to these stimuli. Pre-treatment of trout with a $\beta$-adrenoceptor antagonist (propranolol) prior to exposure to external hypercapnia prevented a sustained hyperventilation despite the absence of significantly elevated catecholamines in the circulation. This revealed that catecholamines of non-humoral origin are involved in the hyperventilatory response to hypercapnia. It is unlikely, at least in trout, that catecholamines play a stimulatory role in the regulation of ventilation. Respiratory acidosis may play a role in the control of ventilation in this species since external hypercapnia prevented the hypoventilatory response normally associated with hyperoxia. (Abstract shortened by UMI.