[Protective effects of melatonin in acute lung injury rats caused by LPS]

To observe the expression of p-p38 mitogen-activated protein kinase in lung tissues of acute lung injury rat model induced by lipopolysaccharide (LPS) and to explore the protective effects of melatonin (MT) in lung tissues in rats.

Seventy-two rats was randomly assigned to three groups, control group, LPS group and LPS + MT group. Rat model of ALI was established by instilling LPS intratracheally. We used immunohistochemical SP and Western blot method to detect the expression of p-p38 mitogen-activated protein kinase in lung tissues and used light microscope to observe morphological changes.

There were rare p-p38 mitogen-activated protein kinase positive cells scattered in alveolar and airway epithelial cells in control group (P < 0.01). The positive p-p38 mitogen-activated protein kinase cells in LPS group increased obviously than those in control group (P < 0.01), and were mainly distributed in infiltrative inflammatory cells, airway epithelial cells, alveolar epithelial cells and pleurames epithelial cells. In MT group, the p-p38 mitogen-activated protein kinase positive cells in airway and lung tissues were much less than those in the LPS group (P < 0.05). The Western blot results were consistent with those of immunohistochemical method.

The expression of p-p38 mitogen-activated protein kinase increases in alveolar and airway epithelial cells in acute lung injury rat models induced by LPS. The activation of p-p38 mitogen-activated protein kinase is found in most lung tissues, suggesting that p-p38 mitogen-activated protein kinase participates in the signal transduction in inflammatory and noninflammatory cells. MT is an effective antioxidant, which relieves the inflammation in acute lung injury rats, possibly through the inhibition of the pathway of p38 MAPK over activation.