Importance of pulmonary ventilation in respiratory control in the bullfrog

Pulmonary and cutaneous O2 consumption (Vo2) and CO2 production (Vco2) were measured simultaneously in bullfrogs Rana catesbeiana at 20 degrees C. The lungs were responsible for 77.3-91.0% of the total Vo2 and 28.5-74.9% of the total VCO2. The distribution of the total exchange between the lungs and skin depended on metabolic rate; frogs with higher rates relied more heavily on the pulmonary mode for both Vo2 and Vco2. When prevented from ventilating their lungs in an O2-rich environment, bullfrogs developed severe respiratory acidosis, demonstrating the importance of lung exchange in normal acid-base balance. When frogs were totally submerged in an O2-saturated medium, skin Vco2 increased linearly to a steady-state value which approximated the preapneic total Vco2. In these same animals, arterial Pco2 increased proportionately to the increase in skin Vco2, indicating that skin diffusion capacity for CO2 was unaffected. We conclude that the control of breathing in the bullfrog in response to changes in metabolic rate relies predominantly on changes in lung ventilation while the skin plays a more passive role.