Data from: Oxidation of linoleic and palmitic acid in pre-hibernating and hibernating common noctule bats revealed by 13C breath testing

Mammals fuel hibernation by oxidizing saturated and unsaturated fatty acids from triacylglycerols in adipocytes, yet the relative importance of these two categories as an oxidative fuel may change during hibernation. We studied the selective use of fatty acids as an oxidative fuel in noctule bats (<i>Nyctalus noctula</i>). Pre-hibernating noctule bats that were fed 13C-enriched linoleic acid (LA) showed 12 times higher tracer oxidation rates compared to conspecifics fed 13C-enriched palmitic acid (PA). After this experiment, we supplemented the diet of bats with the same fatty acids on 5 subsequent days to enrich their fat depots with the respective tracer. We then compared the excess 13C enrichment (APE) in breath of bats for torpor and arousal events during early and late hibernation. We observed higher APE values in breath of bats fed 13C-enriched LA than in bats fed 13C-enriched PA for both states, torpor and arousal, and also for both periods. Thus, hibernating bats oxidized selectively endogenous LA instead of PA, most likely because of faster transportation rates of PUFA compared with SFA. We did not observe changes in APE values in the breath of torpid animals between early and late hibernation. Skin temperature of torpid animals increased by 0.7oC between early and late hibernation in bats fed PA, whereas it decreased by -0.8oC in bats fed LA, highlighting that endogenous LA may fulfil two functions when available in excess: serving as an oxidative fuel and supporting cell membrane functionality.

哺乳动物通过氧化脂肪细胞（adipocytes）内三酰甘油（triacylglycerols）中的饱和脂肪酸与不饱和脂肪酸为冬眠供能，但这两类物质作为氧化供能底物的相对重要性可能在冬眠过程中发生变化。本研究以普通夜蝠（*Nyctalus noctula*）为对象，探究其脂肪酸作为氧化供能底物的选择性利用模式。预冬眠期的普通夜蝠经饲喂富含碳13的亚油酸（linoleic acid, LA）后，其示踪剂氧化速率为饲喂富含碳13棕榈酸（palmitic acid, PA）的同种个体的12倍。本实验结束后，我们在后续5天内为蝙蝠补充饲喂上述同种脂肪酸，以通过对应示踪剂富集其脂肪储备库。随后，我们比较了蝙蝠在冬眠早期与晚期的蛰伏及觉醒过程中，呼出气体中的过量碳13富集度（excess ¹³C enrichment, APE）。我们观察到，无论处于蛰伏还是觉醒状态，亦或是冬眠早期还是晚期，饲喂富含碳13亚油酸的蝙蝠呼出气体中的APE值均高于饲喂富含碳13棕榈酸的蝙蝠。由此可见，冬眠蝙蝠会选择性氧化内源性亚油酸而非棕榈酸，这大概率是因为多不饱和脂肪酸（polyunsaturated fatty acids, PUFA）的转运速率快于饱和脂肪酸（saturated fatty acids, SFA）。我们未观察到蛰伏个体的呼出气体APE值在冬眠早期与晚期间存在变化。饲喂棕榈酸的蝙蝠在冬眠早期至晚期时，其蛰伏个体的皮肤温度升高了0.7℃；而饲喂亚油酸的蝙蝠则降低了0.8℃。这一结果表明，当内源性亚油酸供应充足时，可同时发挥两项功能：作为氧化供能底物以及维持细胞膜功能完整性。