Control of catecholamine release in vivo and in situ in the Atlantic cod (Gadus morhua) during hypoxia

We have characterized the elevation of circulating catecholamines in the intact Atlantic cod (Gadus morhua) during graded acute (30 min) hypoxia. The potential mechanisms contributing to the mobilization of catecholamines during hypoxia were then assessed in vivo using nerve sectioning and pharmacological techniques and in situ using a perfused head kidney preparation. Pre-branchial plasma adrenaline concentrations were significantly elevated at all levels of aquatic hypoxia utilised [water Po, (/VO2) = 10kPa (75mmHg), 7.3kPa (55mmHg) or 5.3 kPa (40mmHg)], whereas noradrenaline levels did not increase significantly in these particular experiments in which PwO2 was lowered gradually over a 30 min period. All subsequent experiments were performed using a more rapid induction of hypoxia to reach a final AvO2 of 5.3 kPa within the first 5-10 min of exposure. Blood withdrawn from pre-branchial (ventral aortic) and post-branchial (dorsal aortic) cannulae after 30 min revealed pronounced re-ductions in PO2 and O2 content (COz) as well as elevated pH. These data support the notion that blood acidosis is not a prerequisite for catecholamine mobilizatio