Comparison of Cell Membrane Phospholipid Fatty Acids in Five Rat Strains Fed Four Test Diets Leslie G. Cleland*,a, Robert A. Glbsonb, Joanna S. Hawkesa and Michael J. Jamesa aMorlalta Trust Bone and Joint Research Laboratory, Rheumatology Unit, Royal Adelaide Hospital, Adelaide and bDepartment of Paediatrics, Fiinders Medical Centre, Bedford Park, South Australia, Australia 559 The fatty acid composition of phospholipids in peritoneal exudate cells and spleen cells was assessed in five rat strains fed four test diets of differing fatty acid composi- tion. Distinctive patterns of fatty acids were seen in the total phospholipid preparations in both cell types in response to the diets which contained either olive, sun- flower, linseed or fish oil. In general, similar fatty acid profiles were seen in each of the rat strains fed the same diet with the only evidence of possible genetic {strain) variation being a relative deficiency of A4 desaturase in Dark Agouti rats. Lipids 25, 559-564 {1990). Following absorption, dietary fatty acids are transported in lipoproteins and taken up by hepatic and other cells, where they may be elongated and desaturated through multiple enzymatic steps {1}. Twenty-carbon fatty acids derived from dietary precursors or provided in the diet can be transferred via plasma lipoproteins to cells throughout the body where they act as substrates for several oxygenase enzymes. Two of these enzymes (cyclo- oxygenase and 5-lipoxygenase) are pivotal in the multi- enzyme pathways which lead to the synthesis of the prostaglandins and leukotrienes (eicosanoids), which have important mediating functions in many homeostatic and pathological processes throughout the body. Thus, the effects of treatments which involve changing the propor- tions of fatty acids in the diet will depend upon multiple metabolic transformations, each of which is potentially subject to varying degrees of biological variation. Under these circumstances, possible genetically determlued diversity in response becomes an important issue. A search for such diversity in rat strains is important as a basis for assessing the likely generality of findings ob- tained in a single rat strain and may also yield a model for metabolic diversity in human populations. Important differences between rat strains have been observed in some relevant experimental settings. For ex- ample, rat strains may differ in their clinical responses to the anti-inflammatory effects of fish-oil supplemented diets on adjuvant induced polyarthritis {2). Rat strains have also been shown to differ in the rate at which they metabolize chylomicrons following fat ingestion (3). Ac- cordingly, the present study was undertaken to assess the extent to which rat strains may vary in their re- sponses to modification of dietary fatty acids in relation to the composition of phospholipid fatty acids in leucocyte membranes. *To whom correspondenceshould be addressed at Rheumatology Unit,Royal AdelaideHospital, North Terrace, Adelaide5000,South Australia,Australia. Abbreviations:AA, arachidonic acid; ALA, a-linolenic acid; DGLA, dihomoylinolenic acid; DHA, docosahexaenoicacid; E PA, eicosapen- taenoic acid;GLC, gas-liquid chromatography; LA, linoleic acid; PBS, phosphate bufferedsaline; TLC, thin-layer chromatography. METHODS Rats. Five rat strains were studied--Dark Agouti, Ginger Hooded, Porton, Sprague Dawley and Hooded Wistar. Weanling rats were obtained from the Gilles Plains Ani- mal Breeding Facility of the South Australian Depart- ment of Agriculture. Cohorts of 16 rats were divided into four groups providing four rats for each dietary treatment group. The rat strains were entered sequentially at 1-week intervals with all animals entering the dietary treatment period at six weeks of age. Studies with Dark Agouti and Hooded Wistar (control)rats were repeated to corroborate differences seen in the Dark Agouti rats in the initial study. Diets. Diets were prepared from fat-freerat chow {Milne Feeds, Perth, Australia) to which the oil supplements were added to achieve a final fat content of 10% {w/w, dry weight). Four oil supplements were used--sunflower {Flora, Unilever Pty. Ltd., Adelaide, Australia), olive {F.H. Faulding & Co. Pty. Ltd., Adelaide, Australia), linseed {Diggers Trading Co., Adelaide, Australia) and fish oil (Maxepa, R.P. Scherer, Melbourne, Australia). Vitamin E was added to achieve a final concentration of 1.84 mg/g oil.The oilsand other constituents were mixed with sufficient water to allow 3 X 3 X 1 cm biscuits to be prepared. These were air dried overnight at room temperature. The food was not examined for lipid oxida- tion, but all diets contained the same levels of vitRmin E. The proportions of major fatty acids in the diets are shown in Table 1. The diets were stored at -20~ until used. The rats were fed test diets and water ad libitum, with food being changed each evening. The diets were con- tinued for four weeks until induction of peritoneal ex- udates. All diets resulted in similar weight gains; e.g., the average weight gain over the four-week period for Porton rats were; olive, 182 g; sunflower, 167 g; linseed, 169 g; and fish, 176 g. TABLE 1 Fatty Acid Profile of Diets a Diet Olive Sunflower Linseed Fish Oleic 18:1n-9 74.0 26.6 22.1 10.0 Linoleic 18:2n-6 8.0 57.7 17.0 1.7 Arachidonic 20:4n-6 -- -- -- 1.1 a-Linolenic 18:3n-3 1.0 1.6 46.8 0.8 Eicosapentaenoic 20:5n-3 -- -- -- 16.5 Docosahexaenoic 22:6n-3 -- -- -- 11.7 aExpressed as percentage of total fatty acids. LIPIDS,Vol. 25, No. 9 0990)