Expression Of INOS And Influence On Thymocyte Apoptosis In The Thymus Of Scald Rat

Objective: To investigate the expression of iNOS in the thymusand and effect of iNOS on thymocyte apoptosis in the scald rat, for exploring the possible mechanism between NO and impairment of thymus after severe scald. Methods: Wistar rats (male , n=56 , 180﹣220g , provided by Animal Science Partment of Jiangxi Medical College ) were randomly divided into 7 groups , there are 8 rats in each group : (1) control group : no scald ; (2) PostBurn-6h group: sacrificed at 6h after scald ; (3) PostBurn-24h group: sacrificed at 24h after scald ;(4) PostBurn-72h group: sacrificed at 72h after scald ;(5) Burn+SMT-6h group : administered SMT (5.0 mg/kg, i.p. q12h) and sacrificed at 6h after scald ;(6) Burn+SMT-24h group :administered SMT and sacrificed at 24h after scald ;(7) Burn+SMT-72h group :administered SMT and sacrificed at 72h after scald ; A 30% total body surface area(TBSA) full-thickness dorsal burn was produced in burn group and burn+SMT group rats by Electrical scald instrument with constant temperature and pressure of 106℃,0.03Mpa for 8s, rats of burn+SMT group were administered SMT(5.0 mg/kg, i.p. q12h) after scald. The weights of thymus ,TUNEL of thymocyte apoptosis and immunohistochemistry of iNOS in thymus were measured at the different indicated times after scald ,respectively. Numerical density of apoptosis's cell and expression of iNOS's cell in thymus at the different indicated times were measured by stereological method. Results: It was shown that: (1) Compared with control group, the weight of thymus continued to decrease during the whole time in burn group, thermal injury resulted in a marked decrease in the weight of thymus at 24h and 72h after scald(P﹤0.01);a marked decrease in the weight of thymus in the burn+SMT group was found at 72h after scald(P﹤0.01); In the mean time, a less decrease in the burn+SMT group at the same indicated time , compared with burn group(P﹤0.01)。(2) Distinct boundary between cortex and medulla ,large number of densely packed thymocytes in the thymic cortex were found in the control group ; at 24h and 72h after scald , corticomedullary junction became indistinct, the thick of thymic cortex and size of thymic lobule were reduced increasingly; there were less structure variation in burn+SMT group at 24h and 72h after scald compared with burn group.(3) The apoptotic thymocytes were aggregated and distributed in cortex ,corticomedullary junction and/or medullary region ;Compared with control group, the numerical density of apoptotic thymocytes were increased in burn and burn+SMT group at the different indicated time(P﹤0.01 or P<0.05); Between burn group and burn+SMT group, there were a marked decreased of apoptotic ratio in the burn+SMT group at 24h and 72h after scald (P﹤0.01)。(4) The iNOS positive cells were distributed adjacent to blood vessel of interlobular septum and thymic cortex ,corticomedullary junction or medullary region at 24h after scald; numerical density of iNOS positive cells were increased distinctly at 72h after scald in burn group, compared with 24h in the same group and control group(P﹤0.01); no iNOS positive cells were found in burn+SMT group。Conclusion: (1) Apoptotic ratio of thymocytes are increased in rat after severe scald. (2) Expression of iNOS are enhanced in the thymus of rat after severe scald. (3) Increasing of iNOS activity can promote thymocyte apoptosis in the severe scald rat. (4) Thymocyte apoptosis can be reduced partly by SMT in the scald rat.