Hyperoxia in the toad, Bufo marinus marinus (L.)

The respiration and blood acid-base regulation of pufo marinus Was examined in nine unrestrained animals during normoxia (PIO₂ = 0.2 atm) and hyperoxia (PIO₂ = 0.6 atm). Arterial blood was serially sampled just prior to O₂ onset, at 1/2, 1, 11/2, 3, 7 and 20 h during hyperoxia and 3 h after exposure, and analyzed for PaO₂, PaCO₂, pHa and [HCO₃⁻]a. Buccal oscillations were recorded for about 5 min before each blood analysis. A significant reduction in mean buccal oscillations occurred during hyperoxia and is attributed to the rise in mean PaO₂. The mean PaO₂ rose to a maximum at 1 1/2 h and declined back towards normal as a result of the decrease in breathing. Mean PaCO₂, pHa and [HCO₃⁻]a did not change significantly during or after the 20 h of hyperoxia, except for the 7 h pHa value. Elevated levels of arterial 0₂ suppressed ventilation in Bufo marinus. The mechanism and location of chemo- reception are unknown. It is postulated that the CO₂ produced by the animal, while its ventilation was reduced, is eliminated through the skin.