Abstract
Dietary fat has recently been shown to influence the metabolic responses to cytokine and endotoxemic models of inflammation. In these studies we have examined the influence of dietary fat on the metabolic responses to turpentine-induced inflammation. Weanling rats were given 20% fat diets based on corn oil, olive oil, butter oil or fish oil (16% olive oil + 4% fish oil) for 6 weeks. Trauma was induced by 3 subcutaneous injections (2ml/kg B.W.) at 48 h intervals. The rats were sacrificed after an overnight fast 6 days after the first turpentine injection along with the respective pairfed controls. Body composition, circulating levels of glucose, glutamine, insulin, total protein, albumin and zinc in serum and RNA, total protein, glutathione, and malondialdehyde (MDA) concentrations in both liver and gastrocnemius muscle were measured. Hepatic zinc and skeletal muscle glutamine concentrations were also estimated. Liver tissue membranes were extracted and their fatty acid profile was analysed. After 6 weeks on the diets membrane lipid fatty acid content, (percent total), reflected dietary intakes with higher C 18:2n-6 in the corn oil (24%) compared with olive oil (8.8%), butter oil (8.4%) or fish oil (10%), and higher C 20:4n-6 in corn oil (14%) and olive oil (17%) compared with fish oil and butter oil (10% each). C 20:5n-3 was incorporated in fish oil fed rats only while C 22:n-3 was highest in fish oil (8.3%) compared with olive oil (3.7%) or butter oil (4%). In response to the turpentine, food intakes fell immediately in all the groups with butter oil (66%), fish oil (62%), olive oil (50%) corn oil (19%). this induced a similar growth inhibition and gradual body weight loss over the 6 day period. Epididymal fat pad sizes were markedly reduced (P<0. 005) in corn oil with lesser reductions in other fats compared to pairfed controls after injury. Liver and spleen enlargements were prominent (P<0.005) in fish oil and olive oil diets. Serum and muscle protein levels decreased significantly in rats fed fish oil, corn oil and olive oil diets. Liver protein mass increased after trauma in rats on wall diets. Liver and muscle RNA concentrations increased (P<0.01) in all diets compared to pairfed controls with fish oil RNA content higher (P<0.01) than corn oil group. Serum and muscle glutamine fell markedly (P<0.01) in all but fish oil diets. A highly significant fall (P<0.001) in serum zinc with concomitant increase in liver was observed in corn oil compared to other fat diets. Liver and muscle glutathione was reduced and MDA elevated after injury in corn oil compared to other fats. Fish oil appeared to resist alterations in glutamine, zinc and MDA concentrations. Glucose tolerance, measured at 10% fat level 24 h posttrauma, was equally good in fish oil and olive oil groups. Butter oil and corn oil exhibited impaired glucose tolerance after injury and an insulin sensitivity half that of fish oil. It would appear therefore that in this rat model, dietary fat at a level significant to alter membrane lipid profiles to an extent which could influence eicosanoid activity and membrane fluidity, does influence the metabolic response to inflammation. Corn oil exacerbates the response while fish oil and, to a lesser extent, olive oil exerts a suppressive effect on the inflammatory response.