Periodic Fluctuations in the Pulmonary Surfactant System in Gould’s Wattled Bat (Chalinolobus gouldii)

Pulmonary surfactant is a mixture of phospholipids, neutral lipids, and proteins that controls the surface tension of the fluid lining the lung. Surfactant amounts and composition are influenced by such physiological parameters as metabolic rate, activity, body temperature, and ventilation. Microchiropteran bats experience fluctuations in these parameters throughout their natural daily cycle of activity and torpor. The activity cycle of the microchiropteran batChalinolobus gouldiiwas studied over a 24‐h period. Bats were maintained in a room at constant ambient temperature (24°C) on an 8L:16D cycle. Diurnal changes in the amount and composition of surfactant were measured at 4‐h intervals throughout a 24‐h period. TheC. gouldiiwere most active at 2a.m. and were torpid at 2p.m. Alveolar surfactant increased 1.5‐fold immediately after arousal. The proportion of disaturated phospholipid remained constant, while surfactant cholesterol levels increased 1.5‐fold during torpor. Alveolar cholesterol inC. gouldiiwas six times lower than in other mammals. Cholesterol appears to function in maintaining surfactant fluidity during torpor in this species of bat.