Simandle E T, Espinoza R E, Nussear K E, Tracy C R
Department of Biology, Colorado State University, Fort Collins, CO 80523-1878, USA.
Physiol Biochem Zool. 2001 Sep-Oct;74(5):625-40. doi: 10.1086/322923.
Our experiments were designed to test the hypotheses that dietary lipids can affect whole-animal physiological processes in a manner concordant with changes in the fluidity of cell membranes. We measured (1) the lipid composition of five tissues, (2) body temperatures selected in a thermal gradient (T(sel)), (3) the body temperature at which the righting reflex was lost (critical thermal minimal [CTMin]), and (4) resting metabolic rate (RMR) at three body temperatures in desert iguanas (Dipsosaurus dorsalis) fed diets enriched with either saturated or unsaturated fatty acids. The composition of lipids in tissues of the lizards generally reflected the lipids in their diets, but the particular classes and ratios of fatty acids varied among sampled organs, indicating the conservative nature of some tissues (e.g., brain) relative to others (e.g., depot fat). Lizards fed the diet enriched with saturated fatty acids selected warmer nighttime body temperatures than did lizards fed a diet enriched with unsaturated fatty acids. This difference is concordant with the hypothesis that the composition of dietary fats influences membrane fluidity and that ectotherms may compensate for such changes in fluidity by selecting different body temperatures. The CTMin of the two treatment groups was indistinguishable. This may reflect the conservatism of some tissues (e.g., brain) irrespective of diet treatment. The RMR of the saturated treatment group nearly doubled between 30 degrees and 40 degrees C. Here, some discrete membrane domains in the lizards fed the saturated diet may have been in a more-ordered phase at 30 degrees C and then transformed to a less-ordered phase at 40 degrees C. In contrast, the RMR of the unsaturated treatment group exhibited temperature independence in metabolic rate from 30 degrees to 40 degrees C. Perhaps the unsaturated diet resulted in membranes that developed a higher degree of disorder (i.e., a certain phase) at a lower temperature than were membranes of lizards fed the saturated diet. Our study demonstrates links between dietary fats and whole-animal physiology; however, the mechanistic basis of these links, and the general knowledge of lipid metabolism in squamate reptiles, remain poorly understood and warrant further study.
膳食脂质能够以与细胞膜流动性变化相一致的方式影响动物整体的生理过程。我们测量了以下指标：（1）五种组织的脂质组成；（2）在热梯度中选择的体温（T(sel)）；（3）翻正反射消失时的体温（临界热最小值[CTMin]）；（4）在三种体温下，给沙漠鬣蜥（Dipsosaurus dorsalis）喂食富含饱和脂肪酸或不饱和脂肪酸的饲料后的静息代谢率（RMR）。蜥蜴组织中的脂质组成总体上反映了其饮食中的脂质，但脂肪酸的具体类别和比例在不同采样器官中有所不同，这表明某些组织（如大脑）相对于其他组织（如储存脂肪）具有保守性。喂食富含饱和脂肪酸饲料的蜥蜴选择的夜间体温比喂食富含不饱和脂肪酸饲料的蜥蜴更高。这种差异与以下假设一致：膳食脂肪的组成会影响膜流动性，而变温动物可能通过选择不同的体温来补偿这种流动性变化。两个处理组的CTMin没有差异。这可能反映了某些组织（如大脑）的保守性，与饮食处理无关。饱和处理组的RMR在30摄氏度至40摄氏度之间几乎翻倍。在这里，喂食饱和饲料的蜥蜴的一些离散膜结构域在30摄氏度时可能处于更有序的状态，然后在40摄氏度时转变为较无序的状态。相比之下，不饱和处理组的RMR在30摄氏度至40摄氏度之间的代谢率与温度无关。也许不饱和饮食导致膜在比喂食饱和饮食的蜥蜴的膜更低的温度下形成更高程度的无序状态（即特定相）。我们的研究证明了膳食脂肪与动物整体生理之间的联系；然而，这些联系的机制基础以及有鳞目爬行动物脂质代谢的一般知识仍然知之甚少，值得进一步研究。
