The effect of alterations in activity and body temperature on the pulmonary surfactant system in the lesser long-eared bat Nyctophilus geoffroyi

Pulmonary surfactant is a mixture of phospholipids, neutral lipids and prot eins that controls the surface tension of the fluid lining the lung. It is critical for lung stability and function. The amount and composition of sur factant are influenced by physiological variables such as metabolic rate, b ody temperature and ventilation. We investigated the plasticity of the pulm onary surfactant system in the microchiropteran bat Nyctophilus geoffroyi t hroughout a natural 24 h cycle. Bats were housed at 24 degrees C on a fixed (8h:16h) light:dark photoperiod, At 4 h intervals throughout the 24 h peri od, bats were lavaged and the surfactant analysed for absolute and relative amounts of total phospholipid (PL), disaturated phospholipid (DSP) and cho lesterol (Chol), N, geoffroyi experienced two peaks of activity, at 18:00 h and 06:00 h, The amount of surfactant increased 1.5-fold upon arousal from torpor. The proportion of DSP to PL in the surfactant remained constant. S imilarly, the Chol/PL and Chol/DSP ratios remained relatively constant. Sur factant cholesterol content did not increase during torpor in N, geoffroyi, Cholesterol does not appear to control surfactant fluidity during torpor i n these bats, but instead the cholesterol content exactly mirrored the diur nal changes in body temperature.