Effects of acute or chronic administration of tumor necrosis factor on rat adipose tissue development

Because tumor necrosis factor (TNF) inhibits adipose cell differentiation in vitro and affects lipid metabolism in vivo, we treated adult or newborn rats for 1 wk with daily intraperitoneal injections (100 U/g of body weight) or continuous intraperitoneal diffusion (3500 U/h) of human recombinant TNF. Three weeks after the end of treatment, the long-term effect of the cytokine was examined on adipose tissue development. Control and TNF-injected rats did not differ in growth or development of perirenal, retroperitoneal and epididymal adipose tissues. Nevertheless, the size distribution of epididymal adipocytes of adult injected rats presented a slight shift towards larger values in the cytokine group. When TNF was administered chronically, the cytokine exerted an anorectic effect, which was alleviated after the end of treatment. The weights of the excised adipose tissues were depressed (P < .025) by TNF administration. Part of this effect was due to the induced anorexia. The size distributions of the epididymal adipocytes of pair-fed and TNF-treated rats were both shifted to smaller (P < 0.01) values than for the controls. The ratio of triglycerides over total lipids was, however, reduced by TNF specifically, but only at the retroperitoneal (P < .05) and not the epididymal site. These results indicate that in contrast to acute treatment, chronic TNF treatment slightly inhibited adipose tissue development in vivo; however, most of this effect was attributable to the associated anorexia.