Hepatic plasma membranes from genetically obese (ob/ob) mice: studies on fluorescence polarization, phospholipid composition and 5'-nucleotidase activity

Regulation of polyunsaturated fatty acid metabolism in tissue phospholipids of obese (fa/fa) and lean (Fa/-) Zucker rats. 1. Effect of dietary lipids on cardiac tissue

The present investigation addressed three questions: (i) Does the obese syndrome alter the fatty acid composition of cardiac tissue and membrane phospholipids in obese (fa/fa) rats? (ii) Are changes, if they occur, similar to those reported for tissues of the genetically obese (ob/ob) mouse? (iii) Can cardiac tissue phospholipids and their component fatty acids be modified by dietary lipids and if so does this occur to the same extent in both fa/fa and lean (Fa/-) rats? Proportions of polyunsaturated fatty acids (PUFA) in cardiac total phospholipids of fa/fa rats differed significantly from those of Fa/- rats and from those reported for ob/ob mice. Increased 18:2n-6 and decreased 20:4n-6 and 22:6n-3 in fa/fa rats indicated impaired PUFA metabolism, possibly reduced delta 6 and/or delta 5 desaturase activity, compared with Fa/- rats. No differences in hepatic delta 6 and delta 5 desaturase activity between fa/fa and Fa/- were found but enhanced activity of delta 9 desaturase activity in fa/fa as compared to Fa/- was evident. Inclusion of sunflower oil (SO) or triolein (TO) at 5% and 20% by weight in the diet elicited marked changes in the fatty acyl composition of cardiac phospholipids in both fa/fa and Fa/- rats when compared with animals fed the control Oxoid diet alone. Supplementation with triolein was most effective, reducing 18:2n-6 and increasing 20:4n-6 proportions in fa/fa rats so that they resembled those in Fa/- rats fed the control Oxoid diet. The type of fat rather than the amount of its dietary intake appears to be the main determinant of the observed changes in phospholipid composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of polyunsaturated fatty acids of the n-3 and n-6 series on lipid composition and eicosanoid synthesis of platelets and aorta and on immunological induction of atherosclerosis in rabbits

The effect of dietary fish oil (rich in n-3 polyunsaturated fatty acids (PUFA], corn oil (rich in n-6 PUFA) and coconut oil (low in n-3 and n-6 PUFA) on the induction of atherosclerosis by serum sickness in rabbits was investigated over a 12-month period. Dietary fish oil led to a significant increase in the level of eicosapentaenoic acid (EPA) in all platelet phospholipid fractions and to a significant reduction in the level of platelet phosphatidylethanolamine arachidonic acid (AA). In aortic total phospholipids, rabbits given fish oil showed a significant reduction in AA and a significant increase in EPA. Rabbits given fish oil showed significantly lower collagen-induced platelet thromboxane A2 release and aortic production of 6-keto-PGF1 alpha. Serum total immune complex levels and anti-horse serum IgG levels were not influenced by diet. There was a significant reduction in total aortic atherosclerosis in fish oil-fed animals compared with coconut oil fed animals.

Hepatic delta 6-desaturase activity in lean and genetically obese ob/ob mice

Hepatic delta 6-desaturase activity is primarily located in the mitochondrial fraction in mice. Both delta 6- and delta 5-desaturase activities are increased in the liver of young (6-week-old) obese mice. The increase in hepatic delta 6-desaturase activity in obese mice does not occur until weaning. Neither restriction of food intake nor hyperinsulinaemia normalize hepatic delta 6-desaturase activity of obese mice. Both cold acclimation and tri-iodothyronine (30 micrograms/day per kg) decreased hepatic delta 6-desaturase activity of obese mice to levels observed in lean mice, whereas the increase in activity in obese mice was still maintained after the induction of hypothyroidism.