BACKGROUND: Subclinical inflammation induced by persistent exposure to lipopolysaccharide (LPS) is found in some clinical conditions such as obesity or diabetes. This study aimed to investigate the effect of recurrent LPS exposure on inflammatory markers, oxidative stress balance and cardiac and renal fibrosis in male rats.METHODS: Male Wistar rats were divided into control and LPS-treated. LPS (۱۰ mg/kg/week) was injected intraperitoneally. After ۴ weeks, left ventricles and kidneys were homogenized and stained with hematoxylin and eosin (H&E) and Masson trichrome for histological examination. Serum levels of nitrite, interleukin ۶ (IL-۶) and tumor necrosis factor-α (TNF-α) were measured and total thiol, malondialdehyde (MDA), superoxide dismutase (SOD) and catalase were evaluated in the heart and kidney homogenates.RESULTS: Serum inflammatory markers were higher in LPS group than control (nitrite: ۳۷.۰ ± ۲.۲ vs. ۲۵.۵ ± ۱.۹ µmol/l; IL-۶: ۸۴ ± ۳ vs. ۹۸.۰ ± ۴.۴ pg/ml; TNF-α: ۷۵.۵ ± ۴.۹ vs. ۸۵.۳ ± ۴.۷ pg/ml; respectively, P < ۰.۰۵۰). Evaluation of total thiol concentration (heart: ۱۰.۰ ± ۰.۹ vs. ۲۲.۵ ± ۱.۲; kidney: ۷.۰ ± ۰.۵ vs. ۲۷.۸ ± ۳.۱ nmol/g tissue, respectively), catalase (heart: ۰.۱۸ ± ۰.۰۳ vs. ۰.۶۶ ± ۰.۰۴; kidney: ۰.۱۷ ± ۰.۰۳ vs. ۰.۷۳ ± ۰.۰۳, U/g tissue, respectively) and SOD (heart: ۸.۰۱ ± ۰.۷۰ vs. ۱۲.۳ ± ۰.۴; kidney: ۷.۰۲ ± ۰.۶۰ vs. ۱۲.۰ ± ۰.۲, U/g tissue, respectively) showed lower levels in LPS-treated group compared to control; while MDA concentration in LPS group was higher than control (P < ۰.۰۵). Histopathological examination in LPS-treated group indicated infiltration of inflammatory cells and more collagen deposition in left ventricle wall and kidney compared to control group.CONCLUSION: We concluded that in clinical conditions with chronic LPS, cardiac and renal fibrosis occurs even in absence of preceding tissue injury due to imbalances in oxidative stress.