HIEBERT, Sara M.*; LEININGER, Elizabeth; HUNERYAGER, Rachel; LE, Lan; TRAN, Thuy; SONG, Joseph; VERARDO, Andrew; Swarthmore College: Environmental regulation of Dietary Lipid Choice in Phodopus sungorus/

Endotherms in cold climates, particularly those entering daily or seasonal torpor, may need to modulate the composition of depot and/or membrane lipids seasonally to regulate membrane fluidity, membrane phase state, membrane leakiness, metabolic availability of depot fats, and/or susceptibility to peroxidation. Previously, hamsters (P. sungorus) have been shown to exhibit temperature-dependent dietary lipid choice when simultaneously offered two diets, high in saturated or unsaturated lipids, respectively. In a study conducted at 21 °C, long-day hamsters treated daily with melatonin acquired the winter phenotype (lightened fur, decreased food consumption, decreased body mass and regressed testes). Relative to long-day controls, melatonin-treated hamsters also significantly increased their preference for the highly unsaturated diet in week 6 of treatment, 2 wks before the first occurrence of spontaneous daily torpor. Thus melatonin, a transducer of photoperiod, is able to stimulate a change in dietary lipid preference that anticipates, rather than simply responds to, temperature changes. These and other experiments examining the relation between the saturation of dietary lipids and thermoregulation used chow supplemented with natural lipids (e.g., beef fat and sunflower oil), which differ not only in saturation but also in proportions of fatty acids of different chain lengths. To control for the latter, we offered hamsters a highly unsaturated diet (chow supplemented with crude soybean oil) and a highly saturated diet (chow supplemented with a mixture of crude and fully hydrogenated soybean oil). As in previous experiments, hamsters exhibited temperature-dependent dietary lipid choice, confirming that saturation is an important variable in dietary lipid selection.