Cardiorespiratory responses of white sturgeon to environmental hypercapnia

Cardioventilatory variables and blood-gas, acid-base status were measured i n cannulated white sturgeon (Acipenser transmontanus) maintained at 19 degr ees C during normocapnic and hypercapnic (Pw(CO2) similar to 20 Torr) water conditions and after the injection of adrenergic analogs. Hypercapnia prod uced significant increases in arterial P-CO2, ventilatory frequency, and pl asma concentration of cortisol and epinephrine, and it produced significant decreases in arterial pH and plasma concentration of glucose but no change in arterial PO2, hematocrit, and concentration of lactate or norepinephrin e. Hypercapnia significantly increased cardiac output (Q) by 22%, mean arte rial pressure (MAP) by 8%, and heart rate (HR) by 8%. However, gut blood fl ow (GBF) remained constant. In normocapnic fish, phenylephrine significantl y constricted the splanchnic circulation, whereas isoproterenol significant ly increased Q and produced a systemic vasodilation. During hypercapnia, pr opranolol 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 alpha- a nd beta-adrenergic modulation. We found microspheres to be unreliable in pr edicting GBF on the basis of our comparisons with simultaneous direct measu rements of GBF. Overall, our results demonstrate that environmental hyperca pnia (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.