ObjectiveTo investigate the therapeutic effect of kinetin on bleomycin A5 (BLM-A5)-induced pulmonary fibrosis in rats. MethodsSixty female Wistar rats were randomly divided into three groups. Group A (n=20) was intratracheally injected with saline as control. Group B (n=20) were intratracheally injected with BLM-A5 to establish pulmonary fibrosis model. Group C (n=20) was intratracheally injected with BLM-A5 and received intraperitoneal injection of kinetin at 0.5 mL/100 g once daily. The rats were sacrificed on the 3rd,7th,14th and 28th day respectively. HE and Masson staining were performed to observe lung pathological changes. The contents of hydroxyproline (HYP),urokinase-type plasminogen activator (u-PA),tissue-type plasminogen activator (t-PA),and PAI-1 in lung and plasma were measured by ELISA. ResultsAlveolitis was most obvious on the 7th day and pulmonary fibrosis was most severe on the 28th day in group B compared with other two groups (P<0.05). Alveolitis and pulmonary fibrosis in group C were significantly alleviated compared with group B (P<0.05),but still more severe than group A (P<0.05). The HYP contents in group B,coincided with fibrosis,began to increase on the 7th day and reached the peak on the 28th day,significantly higher than those in other two groups (P<0.05). The u-PA contents of lung tissue in group B began to decline on the 3rd day,reached the minimum on the 7th day,and was still significantly lower than those in other two groups (P<0.05).On the 14th day, the u-PA contents had no significant difference among three groups. The u-PA plasma contents in group B began to decline on the 3rd day,reached the minimum and had significant difference compared with other two groups on the 7th day (P<0.05),and there was no significantly difference among three groups after the 14th day. The t-PA contents change of lung tissue and plasma in three groups were generally consistent with u-PA,but the t-PA plasma contents in group B were still significantly lower than those in group A on the 14th day (P<0.05). The PAI-1 contents of lung tissue in group B began to increase on the 3rd day,reached the maximum on the 7th day,was still significantly higher than those in other two groups (P<0.05),and there was no significant difference among three groups on the 14th day. The PAI-1 contents in group C decreased compared with those in group B (P<0.05),but still higher than those in group A (P<0.05),and there was no difference among them on the 14th day. The PAI-1 plasma contents in group B began to increase on the 3rd day,reached the maximum and was significantly higher than other two groups on the 7th day (P<0.05),and there was no significant difference among three groups on the 14th day. ConclusionThe contents of u-PA and t-PA are increased by inhibiting PAI-1 generation in lung tissue through kinetin treatment,so that,kinetin can suppress pulmonary fibrosis induced by BLM-A5.