Serotonin transporter inhibition prevents and reverses monocrotaline- induced pulmonary hypertension in rats

Abstract

Background - Progression of pulmonary hypertension (PH) is associated with increased lung expression of the serotonin transporter (5-HTT), which leads to hyperplasia of the pulmonary artery smooth muscle cells (PA-SMCs). Given the postulated causal relation between 5-HTT overexpression and PH, we herein investigated whether the highly selective 5-HTT inhibitor fluoxetine prevented and/or reversed PH induced by monocrotaline (MCT) in rats. Selective 5-HT 1B/1D, 5-HT2A, and 5-HT2B receptor antagonists were used for comparative testing. Methods and Results - MCT injection (60 mg/kg SC) was followed by an early peak in lung 5-HTT expression on day 1, which preceded the onset of PH. Established PH on day 15 was associated with a sustained 5-HTT increase. Continued fluoxetine treatment completely prevented PA-SMC proliferation and PH development and also suppressed the late 5-HTT increase, without affecting the early peak. The 5-HT receptor antagonists did not affect PH. Fluoxetine (10 mg · kg-1 · d -1 PO) started 3 weeks after MCT injection completely reversed established PH, normalizing PA pressure and structure. MCT-induced PH was also associated with increased expression of various cytokines, but only interleukin-1β and monocyte chemotactic protein-1 increased at the early phase and stimulated 5-HTT expression by cultured PA-SMCs. Conclusion - Upregulation of lung 5-HTT induced by MCT appears necessary to initiate the development of pulmonary vascular remodeling, whereas a sustained increase in 5-HTT expression may underlie both the progression and the maintenance of MCT-induced PH. Complete reversal of established PH by fluoxetine provides a rationale for new therapeutic strategies in human PH. © 2005 American Heart Association, Inc.