Factors affecting opening and filling pressures in the lungs of the lizard Pogona vitticeps.

We have previously reported that levels of pulmonary surfactant in the lungs of the lizard Pogona vitticeps increase with increasing body temperature. Static lung compliance decreases with increasing body temperature, and is only marginally affected by the presence of surfactant. Here, we examined the effects of surfactant, temperature, ventilatory pattern and autonomic neurotransmitters on opening and filling pressures. Isolated lungs were ventilated at either 18 or 37 degrees C at low, intermediate and high ventilatory regimes. The effects of acetylcholine and adrenaline were examined using an isolated perfused lung preparation at 27 degrees C. Changing ventilatory pattern or experimental temperature had no effect on either filling or opening pressures. Removal of surfactant increased both opening and filling pressures. Adrenaline administration reduced opening and filling pressures. Normal variations in surfactant levels, which occur with changes in body temperature, do not affect either opening or filling pressures. A critical amount of surfactant may be necessary to prevent adhesion of epithelial surfaces in the lungs of Pogona vitticeps. The anti-glue function of pulmonary surfactant may be more important at 18 than at 37 degrees C.