Ventilation and partitioning of oxygen uptake in the frog Rana pipiens: effects of hypoxia and activity.

Pulmonary and cutaneous oxygen uptake (MO2) and lung ventilation were measured in frogs floating in water with access to air in respirometers, with and without ventilation of the skin provided by stirring. The frogs were exposed to hypoxia in both water and air, and were variably active. In inactive frogs floating in unstirred respirometers at 25 degrees C, 23% of total MO2 is through the skin. Activity of the animal increases total MO2. and also ventilates the skin, so that cutaneous MO2 increases with increasing total MO2. When the respirometer is stirred, cutaneous MO2 increases to 35% of total MO2 in resting animals. Activity no longer affects cutaneous MO2. Lung ventilation volume is directly proportional to lung ventilation rate in normoxia. Ventilation rate, and therefore ventilation volume, is proportional to pulmonary MO2. Ventilation rate approximately doubles in hypoxia (PO2 = 52 mmHg). The pattern of ventilation also changes in hypoxia, from a very irregular pattern in normoxia to one showing regular, large oscillations of lung volume over several ventilation movements. Increased lung ventilation, enhancing pulmonary MO2, is the primary adjustment to increased O2 demand. Partitioning of MO2 shifts towards the lung during both activity and hypoxia. In both cases, however, ventilation of the skin can supplement total MO2 by increasing absolute levels of cutaneous MO2.