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 (Cao2) and an increase in arterial plasma CO2 tension (Paco2). Ammonium bicarbonate (NH4HCO3) infusion did not change ph(a) or Cao2 but increased Paco2 and had no effects on blood pressure or ventilation. In aquatic hyperoxia, HCl infusion lowered pH(a) and Cao2. Arterial blood O2 content, however, was maintained above normoxic levels, and there were no cardiovascular or ventilatory responses to acid-base disturbances in bowfin are correlated with reductions in Cao2 below normoxic levels and not with decreases in pH(a) or increases in Paco2. 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.
