Ventilatory and Cardiovascular Responses to Blood pH, Plasma Pco2, Blood O2Content, and Catecholamines in an Air-Breathing Fish, the Bowfin (Amia calva)

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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 (pHa) and O2, content (Cao2) and an increase in arterial plasma CO2 tension (Paco2). Ammonium bicarbonate (NH4HCO3) infusion did not change pHa or Cao2 but increased Paco2 and had no effects on blood pressure or ventilation. In aquatic hyperoxia, HCl infusion lowered pHa and Cao2. 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 Cao2 below normoxic levels and not with decreases in pHa or increases in Cao2. 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.