Periodic fluctuations in the pulmonary surfactant system in Gould's wattled bat (Chalinolobus gouldii)

Pulmonary surfactant is a mixture of phospholipids, neutral lipids, and pro teins that controls the surface tension of the fluid lining the lung. Surfa ctant amounts and composition are influenced by such physiological paramete rs as metabolic rate, activity, body temperature, and ventilation. Microchi ropteran bats experience fluctuations in these parameters throughout their natural daily cycle of activity and torpor. The activity cycle of the micro chiropteran bat Chalinolobus gouldii was studied over a 24-h period. Bats w ere maintained in a room at constant ambient temperature (24 degreesC) on a n 8L:16D cycle. Diurnal changes in the amount and composition of surfactant were measured at 4-h intervals throughout a 24-h period. The C. gouldii we re most active at 2 A.M. and were torpid at 2 P.M.. Alveolar surfactant inc reased 1.5-fold immediately after arousal. The proportion of disaturated ph ospholipid remained constant, while surfactant cholesterol levels increased 1.5-fold during torpor. Alveolar cholesterol in C.gouldii was six times lo wer than in other mammals. Cholesterol appears to function in maintaining s urfactant fluidity during torpor in this species of bat.