EFFECTS OF HYPERCAPNIA ON BLOOD-GAS AND ACID-BASE STATUS IN THE WHITESTURGEON, ACIPENSER-TRANSMONTANUS

The effect of environmental hypercapnia on respiratory and acid-base v ariables 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 (wa ter PCO2 < 0.5 Torr, 1 Torr = 133.32 Pa), then under hypercapnia (25-3 5 Torr) and a final return to normocapnia at 19 +/- 0.5 degrees C. Acu te (12h) hypercapnia significantly increased arterial PCO2 (8-fold inc rease), ventilation frequency (2-fold increase), plasma HCO3- (2.3-fol d) and decreased arterial pH (to 7.15 +/- 0.02). After 24 h, norepinep hrine, epinephrine and cortisol, were significantly increased, and art erial pH reached its nadir (7.10 +/- 0.03). During the 72- and 96-h-pe riods, 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 si gnificantly to 7.31 + 0.03. The return to normocapnia completely resto red 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, hyperventil ation, a transient norepinephrine ''spike'', and increased plasma cate cholamines, cortisol, and arterial PO2. The respiratory acidosis was o nly partially compensated (35% pH restoration) 96 h after the onset of hypercapnia and resulted in a significantly decreased blood-O-2 affin ity (Bohr effect), as determined by construction of in vitro blood O-2 equilibrium curves at 15 degrees C and 20 degrees C. Prolonged exposu re to hypercapnia may lead to acid-base disturbances and negatively af fect growth of white sturgeon.