Influence of dietary fats on the fluidity of the lipid domains of rabbit plasma lipoproteins.

The effects of dietary stearic and other saturated fatty acids on the fluidity of the plasma lipoproteins were assessed with fluorescence polarization techniques. Rabbits were maintained on diets containing either cocoa butter, milkfat, coconut oil, or corn oil as the only source of fat. Microviscosities eta, of the lipid regions of plasma very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL) were determined by measuring the anisotropy of fluorescence from the probe 1,6-diphenyl-1,3,5-hexatriene. The microviscosity values followed the sequence eta HDL greater than eta LDL greater than eta VLDL when the lipoproteins were isolated from the plasma of rabbits fed cocoa butter, milkfat, or corn oil, HDL and LDL consist of an invariant phase in the temperature range 0--50 degrees C regardless of diet. VLDL from rabbits fed milkfat, corn oil, or cocoa butter displayed monophasic behavior in the same range, while VLDL, from rabbits fed coconut oil showed a phase transition at 31.9 +/- 3.7 degrees C. Lipoproteins were less fluid in fasted than in non-fasted rabbits and VLDL and LDL from fasted milkfat-fed rabbits showed phase transitions. Despite the fatty acid compositions of the dietary fats, VLDL and LDL were more fluid from rabbits fed cocoa butter than from rabbits fed corn oil; apparently metabolism influences microviscosity.