Cardiorespiratory responses of white sturgeon to environmental hypercapnia

Cardioventilatory variables and blood-gas, acid-base status were measured in cannulated white sturgeon ( Acipenser transmontanus ) maintained at 19°C during normocapnic and hypercapnic (PwCO2 ∼20 Torr) water conditions and after the injection of adrenergic analogs. Hypercapnia produced significant increases in arterial Pco 2, ventilatory frequency, and plasma concentration of cortisol and epinephrine, and it produced significant decreases in arterial pH and plasma concentration of glucose but no change in arterial Po 2, hematocrit, and concentration of lactate or norepinephrine. Hypercapnia significantly increased cardiac output (Q) by 22%, mean arterial pressure (MAP) by 8%, and heart rate (HR) by 8%. However, gut blood flow (GBF) remained constant. In normocapnic fish, phenylephrine significantly constricted the splanchnic circulation, whereas isoproterenol significantly increased Q and produced a systemic vasodilation. During hypercapnia, propranolol significantly decreased Q, GBF, MAP, and HR, whereas phentolamine significantly decreased MAP and increased GBF. These changes suggest that cardiovascular function in the white sturgeon is sensitive to both α- and β-adrenergic modulation. We found microspheres to be unreliable in predicting GBF on the basis of our comparisons with simultaneous direct measurements of GBF. Overall, our results demonstrate that environmental hypercapnia (e.g., as is experienced in high-intensity culture situations) elicits stress responses in white sturgeon that significantly elevate steady-state cardiovascular and ventilatory activity levels.