A Study On The Levels Of Serum Lipid And Tumor Necrosis Factor-alpha In Obesity Prone And Obesity Resistant

IntroductionThe incidence of obesity has increased obviously accompany ing the development of economy and the change of human living form. Obesity has been thought of a crucial risk factor for developing hypertention, coronary heart disease, noninsulin dependent diabetes mellitus, stroke and so on. Therefore, it has an important meaning to investigate the mechanism of obesity and to prevent the occurring and developing of obesity.It is difficult to study obesity in humans because of many reasons. Models have been utilized to acquire information which would not otherwise be obtainable. Perhaps the most relevant of these models with regard to human obesity are those in which obesity develops in response to increased dietary fat. Levin found that part of the rats fed the same high fat diet was obese and part was not obese in 1983. The former group is referred to as obesity prone (OP), whereas the latter group is referred to as obesity resistant (OP).High-fat diet is a significant contributor to hyperphagia, weight gain, and fat deposition. This higher fat content has been associated with metabolic and endocrine changes that promote fat storage. Such as hypertriglyceridemia, hypercholesterolemia, hyper leptinemia andso on. Recent studies have shown that cytokine, especially tumor necrosis factor-alpha, may affect lipid metabolism and obesity. TNF-α may be another crucial component of obesity and its complication. Recently it has been shown that fat tissue is a significant source of endogenous TNF-a production. In human obesity and animal obese models, expression of this cytokine in adipose tissue and its levels in serum are higher than in lean controls. TNF-α appears to play a critical role as a mediator of the perpheral insulin resistance. Now there is no report in our country about how the TNF-a levels change and what causes the change and the relation between TNF-a and obesity. The text utilizes the above animal models to extermine the levels of serum lipid and TNF-a in order to find the action of TNF-α in lipid metabolism and obesity and provide theoretial basis for the study of obesity.ObjectiveThe purposes of this experiment are:1.Assessing early and late serum lipid changes induced by high-fat diet in obesity-prone and obesity resistant rats.2.Investigating the levels of TNF-α in obesity-prone and obesity resistant rats.3.Investigating if TNF-α is related to obesity and its complication.Materials and Methods Animals and Diets. Thirty-two male Sprague-dawley ratsweighting 120±10g were obtained from the Animal Department of China Medical University. Animals were individually housed in cages in a temperature-controlled room (22±5℃) with a 12-hour light/ dark cycle. Animals were given free access to diets and water over the duration of the study. For induction of obesity, 22rats were given a high-fat diet and 10 rats were given a standard diet as control. The composition of diets is listed on Table 1.Experimental procedures. Both groups of mice were initially fed a standard diet for 1 week before the high-fat or control diets were started. All rats were maintained on their allotted diet for 14 weeks.At the end of every week in the entire study period, body weights and food intake were measured At each time point (1,3,14 weeks) rats were given fast for 24h before blood were sampled at the eye vein. All samples were immediately centrifuged, and the serum was stored at -20α. All rats were killed by decapitation at the end of week!4.Over the 14-wk period, rats fed the high-fat diet diverged into two groups based on body weight gain. The rats with the greatest weight gain were referred to as obesity-prone, others were referred to as obesity-resistant. Abdominal fat pads (peri-renal, epididymal, and mesenteric) were excised, weighed, and frozen.Assays. Serum total cholesterol(TC), triglyceride(TG), high density lipoprotein cholesterol(HDL-C) levels were assayed with enzymatic kits. Serum TNF-a concentrations were determined by radioimmunoassay.Statistical method...