AIM: To explore the mechanism of nitrendipine (NIT) in the prevention and treatment of pulmonay hypertension induced by monocrotaline (MCT). METHODS: 5 hydroxytryptamine (5 HT) and 5 HT receptors (5 HTR) in pulmonary tissue were observed by immunohistochemistry and image analysis system. Cellular growth, constriction function and free Ca 2+ in cultured pulmonary arterial smooth muscle cells were measured by the methods of MTT, morphometry and calcium fluorescent probe Fura 2 Am. RESULTS: NIT restrained the number of MCT induced positivecells in pulmonary tissue (from 127 494±20 736 to 23 814±13 284/mm 2, P <0.01) and the relative contents( value of A: 1.16±0.26 to 0.30±0.17, P <0.01) of 5 HT and 5 HTR(from 14 624±3 010 to 4 875±972/mm 2, P <0.01, value of OD: 0.83±0.16 to 0.72±0.15) respectively. Both the cellular growth and the contraction of pulmonary arterial smooth muscle cells induced by 5 HT were inhibited significantly by NIT at 10 -8 mol/L. 5 HT induced (242±12 nmol/L) free Ca 2+ in cultured pulmonary arterial smooth muscle cells was prevented by NIT(126±9 nmol/L), which might be related to the inhibitory effect the NIT on the Ca 2+ influx. CONCLUSION: NIT can reduces the number and contents of 5 HT and 5 HT receptors in pulmonary tissue and plays an important role in the prevention and treatment of MCT induced pulmonary hypertension.