Effects of dietary polyunsaturated fatty acids on rat brain plasma membrane fatty acid composition

The effects of four different diets on phospholipid fatty acid composition of rat brain plasma membranes were evaluated. Rats were given a semisynthetic diet in which lipids were supplied by 5 per cent peanut oil (n-3 PUFA deficient diet), cod liver oil (n-6 PUFA deficient diet), partially hydrogenated palm oil (total PUFA deficient diet) or a mixture of peanut and rapeseed oil (control group). Animals fed the total PUFA deficient diet had significantly lower body and brain weights than the control group (p<0.05). Lower brain cholesterol and phospholipids also were observed in animals fed the total PUFA deficient diet, whereas the brain of animals fed the n-6 PUFA deficient diet had higher levels of these lipid components than the control group (p<0.05). Phosphatidylcholine and phosphatidylethanolamine were mutually replaced in animals fed the n-6 and n-3 PUFA deficient diets, so that the sum of these two membrane constituents was maintained around 77 per cent of total phospholipids. Brain phospholipid fatty acid composition was significantly modified by the diets studied. Thus, despite being a highly protected organ, the fatty acid composition of the brain can be extensively modulated by dietary lipids.

Effects of dietary polyunsaturated fatty acids on adenylate cyclase, 5'nucleotidasa and Na+K+-ATPase activities in rat brain-plasma membrane

The incidence of polyunsaturated fatty acids (PUFA) in human nutrition is now generally accepted. As essential membrane components, PUFA may act as enzyme activity modulators. In this study, four different diets, in which PUFA type was the only modifying factor, were evaluated on 5'nucleotidase, adenylate cyclase and Na+/K+ATPase activities in rat brain plasma membranes. Animals fed the total PUFA deficient diet exhibited significant lower body weight and lower brain weight than did the control group. The specific activities of 5'nucleotidase and Na+/K+ATPase in brain plasma membrane were slightly modified by dietary PUFA. The catalytic unit of adenylate cyclase in total PUFA deficient animals presented augmented enzyme activity and animals receiving diets deficient in n-6 PUFA showed reduced activity in relation to the control animals. Our results showed that the epinephrine receptors, in the case of adenylate cyclase are not modified by dietary PUFA, but rather the catalytic unit seems to be altered by dietary PUFA. These results can be partially explained by the fluidity that PUFA confers to membranes facilitating the proximity of enzyme-substrate. The physiological consequences of dietary PUFA incidence on enzyme activity needs further study.