Respiratory, Ventilatory, Acid-Base And Ionoregulatory Physiology Of The White Sucker Catostomus Commersoni: The Influence Of Hyperoxia

Blood gases, acid-base status, plasma ions, respiration, ventilation and cardiovascular function were measured in white suckers, using standard cannulation methods. Basic respiratory parameters under normoxia were compared to those in the active, pelagic rainbow trout and in other benthic teleosts. Sustained environmental hyperoxia (350-550 torr) increased arterial O₂ (102-392 torr) and venous O₂ (17-80 torr) tensions so that blood O₂ transport occurred entirely via physical solution. Dorsal aortic blood pressure and heart rate fell, the latter due to an increase in vagal tone. Ventilation volume declined markedly (by 50%) due to a decrease in ventilatory stroke volume, but absolute O₂ extraction rose so that O₂ consumption was unaffected. While the preceding effects were stable with time, arterial and venous CO₂ tensions approximately doubled within 4 h, and continued to increase gradually thereafter. This CO₂ retention caused an acidosis (7·993-7·814) which was gradually compensated by an accumulation of plasma [HCO₃^–]. However, even after 72 h, arterial pH remained significantly depressed by 0·10 units. The gradual rise in plasma [HCO₃^–] was accompanied by a progressive fall in both [Na⁺] and [Cl^–] ; [K⁺] and [Ca²⁺] remained unchanged. The responses of the sucker to hyperoxia are compared to those of the rainbow trout.