Respiratory mechanisms and acid-base regulations in Bufo marinus marinus (L.)

Respiratory and circulatory changes which occur on exposure to elevated ambient carbon dioxide levels were studied in free-moving Bufo marinus. The buccal cavity, lungs, and systemic arch were cannulated singly or in combination. Simultaneous recordings from the lung and buccal cavity permitted analysis of respiratory rate and pattern. Serial blood sampling from the systemic arch allowed constant monitoring of arterial gas tensions. All experiments were conducted at 220 Cc. Normal breathing pattern consisted of continuous buccal oscillations with irregularly occurring lung ventilations. High pressure inflations occurred infrequently. On exposure to increased ambient carbon dioxide levels, oscillations decreased, ventilations increased, and inflations predominated. It is postulated that ventilatory response to carbon dioxide is mediated by chemoreceptive and baroreceptive areas in the animal, Normal arterial pH and gas tensions varied among individuals, but the changes due to elevated ambient CO₂ tensions (PᵢCO₂) were constant. At all levels of PᵢCO₂, arterial pH decreased significantly but the magnitude of the decrease depended on PᵢCO₂. Arterial oxygen tensions (PₐCO₂) remained unchanged at low PᵢCO₂, but increased significantly as PᵢCO₂ exceeded 20 - 25 torr. At low levels of PᵢCO₂, arterial CO₂ tensions (PₐCO₂) rose to a value greater than PᵢCO₂, creating a gradient to the exterior. When PᵢCO₂, reached 30 - 35 torr, P CO, did not rise to the same level, but remained approximately 10 torr lower. Buffer capacity and % pH regulation were calculated for all ; animals, It is suggested that the PᵢCO₂/PₐCO₂ differential might be due to a transport system involving Na⁺, H⁺ and HCO₃⁻.