Control of breathing in an amphibian Bufo paracnemis: effects of temperature and hypoxia.

Lung ventilation was measured in the toad, Bufo paracnemis, weight 500-800 g, at 15, 25 and 32 degree C during normoxia and hypoxia (5, 10, and 15% inspired O2). Arterial blood gases were measured during normoxic breathing. Typically breath-holds alternated with ventilatory periods, which were initiated by a stepwise pulmonary deflation. Then a series of breaths consisting of both expiratory and inspiratory volumes followed. At the end of the period the lungs were inflated in several steps. Increased temperature markedly augmented ventilation mostly through a five-fold increase in the number of ventilatory periods per unit time. Ventilation was also enhanced by hypoxia and this response was greatest at the highest temperature. Arterial PO2 rose from 35 to 96 Torr when temperature increased from 15 to 32 degrees C. Bufo resembles reptiles regarding these responses.