Polyunsaturated fatty acid deficiencies: effects on hepatic plasma membrane fatty acid composition and enzyme activity.
Research on dietary polyunsaturated fatty acids (PUFA), on the activity of 5'nucleotidase and adenylate cyclase are largely contradictory due, mostly, to the absence of adequate control group. In this study; four different diets have been evaluated on the 5'nucleotidase and adenylate cyclase activities in rat liver plasma membranes. Wistar rats were given a semisynthetic diet in which lipids were supplied by 5% of either peanut oil (n-3 PUFA deficient diet), cod liver oil (n-6 PUFA deficient diet) partially hydrogenated palm oil (total PUFA deficient diet) and a mixture of peanut and rapeseed oil (control group). Liver plasma membranes were separated by using a Percoll gradient in a Beckman JA 20 centrifuge. 5'nucleotidase and adenylate cyclase activities were measured in a liquid scintilation detector by following the degradation of 3HAMP (adenosine monophosphate) and production of 3HcAMP (cyclic adenosine monophosphate) respectively. Animals fed the total PUFA deficient diet exhibited significant lower body weight and lower liver weight than did the control group. Low cholesterol concentrations were observed in animals deficient either in n-3 or total PUFA in relation to the control group. All dietary deficiencies studies provoked reduced phospholipid levels. Phosphatidylcholine and phosphatidylethanolamine were not modified whatever the deficiency studied. Phospholipids fatty acid composition was significantly modified by the diets studied. The specific activity of 5'nucleotidase in hepatic plasma membrane was independent of dietary PUFA. The catalytic unit of adenylate cyclase complex in totally deficient animals was augmented. The unit of the enzyme stimulated by the guanydyl imidodiphosphate (GppNHp) in n-3 PUFA deficient animals was augmented and reduced in animals receiving the n-6 PUFA deficient diet. In conclusion, our results show that each dietary PUFA deficiency modifies differently the proportions of phospholipid classes and their fatty acid composition. The mechanisms responsible for these modification remain to be elucidated. However, the phospholipid fatty acid changes did not influence the 5'nucleotidase activity except in the case of extreme excess which concerns more toxicology than nutritional modifications. Finally, the catalytic unit (Forskoline + GDP beta s) of adenylate cyclase complex and the regulatory unit (GppNHp) may be sensitive to alterations in PUFA composition.
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