AN INVESTIGATION OF THE ROLE OF CIRCULATING CATECHOLAMINES IN THE CONTROL OF VENTILATION DURING ACUTE MODERATE HYPOXIA IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Gill ventilation volume ( {Mathematical expression}w), arterial blood oxygen tension (PaO2) and arterial blood oxygen content (CaO2) of rainbow trout (Oncorhyncus mykiss) were monitored during normoxia [water PO2 (PwO2) ∼155 Torr], hypoxia (PwO2=72±5.8 Torr), or hyperoxia (PwO2=643±32 Torr). Fish hyperventilated during acute (30 min) hypoxia and hypoventilagted during acute hyperoxia. Plasma catecholamine levels were unchanged after 30 min of hypoxia or hyperoxia. In addition, selective adrenoceptor blockade with either propranolol (β-adrenoceptor antagonist) or phentolamine (α-adrenoceptor antagonist) did not modify the hyperventilatory response during hypoxia. These results indicate that circulating catecholamines are not involved in the control of ventilation in moderately hypoxic rainbow trout. In the summer, intra-arterial infusion of catecholamine in normoxic trout caused transient (adrenaline) or persistent (noradrenaline) hypoventilation. These observations also do not support a role for catecholamines in the stimulation of ventilation. During hypoxia, PwO2, PaO2 and CaO2 were depressed whereas during hyperoxia, only PwO2 and PaO2 was elevated significantly. Thus, it is suggested that the hypoventilatory response to hyperoxia is mediated by a direct effect of elevated PwO2/PaO2, whereas the hyperventilatory response to hypoxia is mediated by changes in PwO2/PaO2, and/or CaO2. © 1990 Springer-Verlag.