Inhibitory effects of melatonin on the expression of phosphorylation p38 mitogen-activated protein kinase during acute lung injury in rats

Abstract

To investigate the protective effect of melatonin (MT) on lung tissues during acute lung injury (ALI) in rats and its possible mechanism. Seventy-two Sprague-Dawley (SD) rats were randomly divided into three groups: control group, lipopolysaccharide (LPS) group and MT treatment group. In LPS group and MT treatment group, 1 ml/kg of LPS (200 mug/200 mul) was administered through the airway. In MT group, 10 mg/kg of MT was injected intraperitoneally before and after administration of LPS, and 1 ml/kg of ethanol-normal saline was given in control rats. The rats were sacrificed at 3, 6, 10 hours after administration of LPS, and the lung tissue was obtained for determination of the contents of nitrogen monoxide (NO) and malondialdehyde (MDA), and activity of superoxide dismutase (SOD). In addition, the expression of phosphorylation p38 mitogen-activated protein kinase (p-p38 MAPK) in lung tissue was assayed with immunohistochemistry staining. Compared with control group, SOD activity (U/mg) decreased significantly in LPS group (3 hours: 73.78+/-3.62 vs. 112.69+/-3.26, 6 hours : 66.07+/-2.31 vs. 117.85+/-1.96, 10 hours: 55.13+/-5.26 vs. 118.27+/-2.16, all P<0.01), but NO (micromol/mg), MDA (nmol/mg) content and the expression of p-p38 MAPK [absorbance (A) value] increased obviously (NO: 8.19+/-0.48 vs. 2.32+/-0.20 at 3 hours, 11.71+/-0.27 vs. 2.08+/-0.15 at 6 hours, 16.53+/-0.60 vs. 2.76+/-0.21 at 10 hours; MDA: 11.43+/-0.68 vs. 2.86+/-0.21 at 3 hours, 19.63+/-1.29 vs. 2.85+/-0.19 at 6 hours, 26.63+/-2.00 vs. 2.84+/-0.28 at 10 hours; p-p38 MAPK: 0.340+/-0.020 vs. 0.238+/-0.019 at 3 hours, 0.410+/-0.016 vs. 0.218+/-0.024 at 6 hours, 0.578+/-0.066 vs. 0.238+/-0.036 at 10 hours, all P<0.01). The administration of MT mitigated above contents significantly [SOD (U/mg) was 86.02+/-2.81, 80.87+/-3.40, 94.46+/-5.03, NO (micromol/mg) was 3.80+/-0.28, 5.32+/-0.22, 7.24+/-0.52, MDA (nmol/mg) was 8.18+/-0.84, 7.84+/-0.78, 6.43+/-1.06, and p-p38 MAPK (A value) was 0.311+/-0.018, 0.312+/-0.019, 0.314+/-0.021 at 3, 6, 10 hours, respectively, P<0.05 or P<0.01]. MT possessed protective effect on lung tissues during ALI by its antioxidation effect and inhibition of over- expression of p-p38 MAPK.