Thermal cycling of the pulmonary surfactant system in small heterothermic mammals

Pulmonary surfactant is a complex mixture of lipids and proteins secreted b y alveolar type II cells into the fluid lining the interface. Surfactant lo wers surface tension, maintains alveolar stability, increases lung complian ce and helps to prevent pulmonary edema. Surfactant secretion is principall y regulated by changes in breathing pattern and autonomic output. Heterothe rmic mammals provide an opportunity to examine how the surfactant system re sponds to changes in physiological condition. Being composed largely of lip ids the pulmonary surfactant system is especially sensitive to changes in b ody temperature. In Sminthopsis crassicaudata and Chalinolobus gouldii chol esterol appeared to function to maintain fluidity during torpor. However Ch alinolobus gouldii and Nyctophilus geoffroyi were found to have to have the lowest levels or. cholesterol of any mammal studied to date suggesting tha t the surfactant proteins may also play a role in maintaining fluidity in t hese animals.