Chronic use of 5-HT_2B receptor (5-HT_2B-R) agonists (anorectic drugs or ergot derivatives) has been associated with left cardiac valve injury but the mechanisms are unclear. Lesions are characterised by increased thickness and cellularity with massive extracellular matrix production. This work was designed to study contribution of 5-HT_2B and 5-HT_2A-R and the link with their activation and endothelial nitric oxide in valve degeneration. We validated an experimental mouse model of valvulopathy by infusing (28 days; Alzet^® pumps) the selective 5-HT_2B-R agonist (nordexfenfluramine: NdF 1mg/kg/day) and designed 13 groups: 5 groups of WT mice (129svPas; 12 weeks): 1) control (C); 2) NdF; 3) NdF+ritanserine (2mg/kg/day); 4) NdF+SB206553 (1mg/kg/day); 5) NdF+LNAME (300mg/kg/day); 8 groups of transgenics: 6) 5-HT_2B^-/--C; 7) 5-HT_2B^-/-- NdF; 8) 5-HT_2A/2B^-/--C; 9) 5-HT_2A/2B^-/--NdF; 10) 5-HT_2A^-/--C and 11) 5-HT_2A^-/-- NdF and 2 groups of eNOS^-/- mice 12) eNOS^-/--C and 13) eNOS^-/--NdF. Mice were monitored for hemodynamic and echocardiographic parameters. At day 28, blood 5-HT and urinary 5-HIAA concentrations were measured and hearts harvested for histological analysis. In controls, this analysis reveals mitral valve lesions with increased thickness (WT-C 35±4μm vs WT-NdF 69±9μm; p<0,05) and number of endothelial cells (+40%). Lesions are fully prevented by pharmacological and constitutive inactivation of: 5-HT_2B-R (SB 206553 or 5-HT_2B^-/- mice) and both 5-HT_2A and 5-HT_2B-R (ritanserine or 5-HT_2A/2B^-/-). In 5-HT_2A^-/- treated with NdF, we still observe an increased valve thickness (5-HT_2A^-/--C 45±4μm vs 5-HT_2A^-/--NdF 60±8μm) mainly due to increased cellularity. Finally, eNOS inhibition (L-NAME or eNOS^-/- mice) also prevents lesions indicating the crucial role of endothelial cells in 5-HT_2B-mediated mitral valve degeneration.

We demonstrate for the first time that both 5-HT_2B and 5-HT_2A-Rs are involved in drug-induced valvulopathy and the role of endothelial cells and eNOS activation.