Abstract: Objective Imitating clinical etiology of congestion of pulmonary vessels, the model of diffuse pulmonary hemorrhage was established in immature rats for research on pulmonary hemorrhage in the newborn. Methods Twenty four rats were divided randomly into experimental group and control group （n=12 each ）.The experimental group received 0.1% epinephrine by subcutaneous injection b.i.d. The dosage of epinephrihe was 0.2 mg/kg /dose at first day，0.3 mg/kg/dose at the second day，and was increased gradually to 0.8 mg/kg/dose at the seventh day，The control group received normal saline at the same volume. After rats died or were killed，the lungs were removed and the degree of pulmonary hemorrhage was divided into five grades according to macroscopy：Grade Ⅰ （normal lung），Grade Ⅱ （pulmonary edema ），Grade Ⅲ （ spotty pulmonary hemorrhage ），Grade Ⅳ （local pulmonary hemorrhage ）and Grade Ⅴ （diffuse pulmonary hemorrhage ）. The lung samples were also observed by optical and electron microscope. Results The average days injected epinephrine are 5.25±1.82 day.Macroscopic examination showed Grade V in 10 rats，Grade IV in 1 rat and Grade Ⅲ in 1 rat in the experimental group , and all the control group was Grade I . By the RIDIT analysis，a significant （X²=18.00,P＜0.01）. Optical microscopy exam showed ex-tensive accumulation of red blood cell in the alveolar spaces and serious dilatation and congestion in the small vessels and capillaries for Grade V. Electron microscopy exam showed local disintegration of epithelial layer, thinning and discontinuity of blood-gas barrier for Grade V. Conclusions The model of diffuse pulmonary hemorrhage in immature rats can be established with epinephrine by subcutaneous injection from serious congestion of pulmonary vessels .

Key words: Newborn, Pulmonary, Hemorrhage, Rats, Pathology.