Effects And Mechanism Of Fluoxetine On The Evolution Of Monocrotaline-induced Pulmonary Arterial Hypertension In Rats

Objective To investigate the short-term and long-term therapeutic effects of fluoxetine on monocrotaline-induced PAH and associated pathophysiologic alterations in PAH models.Methods 110 Wistar rats were randomly distributed into four groups.Rats in M+F group received a single subcutaneous injection of MCT (60 mg/kg) and then were given fluoxetine (10 mg/kg) once daily by gavage from week 4 to 12. Another group (M/F) received a single subcutaneous injection of MCT (60 mg/kg) and then were given fluoxetine (10 mg/kg) once daily by gavage from week 4 to 6. The third group (MCT) received a single subcutaneous injection of MCT (60mg/kg) and then were given an equivalent volume of saline gavage from week 4. The fourth group (Saline) received only an equivalent volume of 0.9% saline injection or gavage throughout the experiment. Morphometric changes, right ventricular pulmonary pressure (RVSP), percent wall thickness (PWT), right ventricular hypertrophy index (RVHI) and serotonin transporter (5-HTT) expressions were detected at various times during the 12-week observation. Besides, pulmonary artery smooth muscle cells isolated from Wistar rats were cultured and intervered to investigate the possible effect on PASMC proliferation. PASMC involved in the in vitro analysis was assigned into four groups:(1) Control group:cells were cultured with fetal bovine serum (FBS,10%) in regular condition; (2) 5-HT group: cells were given FBS and 5-HT (5μg/ml) in regular condition; (3) Flu group:cells were given FBS and fluoxetine (5μg/ml-80μg/ml) in regular condition; (4) 5-HT+Flu group: cells were given both 5-HT and fluoxetine together with 10% FBS and were cultured under regular condition. MTT method and Flowcytometry were used to evaluate the proliferation and changes of PASMC cell cycle at various timepoints.Results (1) an aggravation of right ventricular hypertrophy and the completely reversed PAH was noted 6 weeks after fluoxetine withdrawal in M/F group, while such signs were observed in M+F group; (2) 5-HTT protein levels were significantly raised in M/F group after fluoxetine discontinuation, which was paralleled with the severity of PAH; however, no upregulation of 5-HTT was found in M+F group. An in vitro study of PASMC revealed that the A490 value in 5-HT+Flu group was statistically reduced compared with that of 5-HT group. The FCM analysis revealed that the percentage of cell number within phase G0/G1 was greated increased as a result of 72 h fluoxetine administration.Conclusion (1) Fluoxetine is effective in reversing MCT-induced pulmonary vascular remodeling and ameliorating right ventricular hypertophy in rats, which is associated with inhibition of overexpression of 5-HTT. (2) Continuous fluoxetine administration is more effective than short-term administration in preventing recurrence of PAH in rats. (3) 5-HT is confirmed to markedtly promote proliferation of PASMC, which can be effectively inhibited by administration of fluoxetine; the underlying mechanism may be associcated with inhibition of transformation of DNA within different phases.