Effects of hypercapnia on blood-gas and acid-base status in the white sturgeon, Acipenser transmontanus

The effect of environmental hypercapnia on respiratory and acid-base variables was studied in white sturgeon, Acipenser transmontanus. Blood PCO2, PO2, pH, hemoglobin concentration, and plasma lactate, glucose, catecholamines and cortisol were measured first under normocapnia (water PCO2 < 0.5 Torr, 1 Torr = 133.32 Pa), then under hypercapnia (25-35 Torr) and a final return to normocapnia at 19 +/- 0.5 degrees C. Acute (12h) hypercapnia significantly increased arterial PCO2 (8-fold increase), ventilation frequency (2-fold increase), plasma HCO3- (2.3-fold) and decreased arterial pH (to 7.15 +/- 0.02). After 24 h, norepinephrine, epinephrine and cortisol, were significantly increased, and arterial pH reached its nadir (7.10 +/- 0.03). During the 72- and 96-h-periods, arterial PCO2 (24 +/- 4.4 Torr) and ventilatory frequency (105 +/- 5 breaths min(-1)) stabilized, HCO3- reached its apparent maximum (23.6 +/- 0.0 mmol(-1)), glucose decreased by 32%, and pH increased significantly to 7.31 + 0.03. The return to normocapnia completely restored arterial PCO2 (2.5 +/- 0.14 Torr), HCO3- (7.4 +/- 0.59 mmol.l(-1)), ventilation frequency (71 +/- 7 breaths.min(-1)), and pH(7.75 +/- 0.04). Overall, hypercapnia produced a respiratory acidosis, hyperventilation, a transient norepinephrine "spike", and increased plasma catecholamines, cortisol, and arterial PO2. The respiratory acidosis was only partially compensated (35% pH restoration) 96 h after the onset of hypercapnia and resulted in a significantly decreased blood-O-2 affinity (Bohr effect), as determined by construction of in vitro blood O-2 equilibrium curves at 15 degrees C and 20 degrees C. Prolonged exposure to hypercapnia may lead to acid-base disturbances and negatively affect growth of white sturgeon.