The effect of dietary essential fatty acid deficiency on the composition and properties of the liver microsomal membrane of rats.

The effect of dietary essential fatty acid (EFA) deficiency on lipid composition, fluidity and important enzyme and transport activities of liver microsomal membrane was studied in weanling rats. After 133 d of EFA deficiency, no difference was noticed in membrane phospholipid, cholesterol and protein levels, but a significant change occurred in the fatty acid composition of bilayer phospholipids. In EFA-deficient rats, linoleic (18:2(n-6] and arachidonic (20:4(n-6] acids were both severely lower while oleic (18:1(n-9], palmitoleic (16:1(n-7] and particularly 5,8,11-eicosatrienoic (20:3(n-9] acids were significantly higher than in controls. The higher level of the latter tended to compensate for the lower level of 20:4(n-6). Membrane fluidity, as estimated by the reciprocal of the order parameter S, was lower in the deficient rats than in the controls, and all the measured microsomal enzyme activities were markedly affected. NADH-Cyt b5 electron transferring system, coupled with the fatty acid desaturation system, was higher than in controls. In contrast, the cytochrome P450 complex activity was lower and some of the important liver detoxifying enzyme activities were lower due to physical-chemical changes in the microsomal membrane. Calcium uptake and Ca2+-ATPase activity were also significantly lower in EFA-deficient rats than in controls. It was concluded that fatty acid composition may be the major factor contributing to membrane fluidity and function and that EFA might play a role in regulating the intrinsic membrane protein activities.