Résumé
Hydrochloric acid (HCl) infusion during aquatic normoxia increased blood pressure, gill ventilation, and air breathing in bowfin. These responses were associated with a reduction in arterial blood pH ($pH_{a}$) and O₂, content ($Ca_{O_{2}}$) and an increase in arterial plasma CO₂ tension ($PaCO_{2}}$). Ammonium bicarbonate (NH₄HCO₃) infusion did not change$pH_{a}$or$Ca_{O_{2}}$but increased$Pa_{CO_{2}}$and had no effects on blood pressure or ventilation. In aquatic hyperoxia, HCl infusion lowered$pH_{a}$and$Ca_{O_{2}}$. Arterial blood O₂ content, however, was maintained above normoxic levels, and there were no cardiovascular or ventilatory responses. These results indicate that cardiovascular and ventilatory responses to acid-base disturbances in bowfin are correlated with reductions in$Ca_{O_{2}}$below normoxic levels and not with decreases in$pH_{a}$or increases in$Pa_{CO_{2}}$. Hydrochloric acid infusion in normoxia stimulated a release of endogenous catecholamines, whereas NH₄HCO₃ infusion and HCl infusion in hyperoxia did not. Catecholamine infusion stimulated gill ventilation but not air breathing. The correlation between increases in plasma catecholamines and gill ventilation following HCl infusion in normoxia indicates that circulating catecholamines may contribute to gill ventilatory responses to hypoxemia in bowfin.