Amitriptyline (AM) is a classical and typical tricyclic antidepressant drug. Despite its well-known effects on the nervous system, it has been described to work as a TLR4 antagonist and several clinical works suggested some unexpected cardiovascular effects. The role of amitriptyline on vascular tone is not clear, thus we hypothesized that amitriptyline has a double effect on vascular tone by both endothelial TLR4-dependent nitric oxide down-regulation and calcium channel blockade in smooth muscle cells.

Changes in isometric tension were recorded on a wire myograph. NO production was evaluated by fluorescence microscopy and flow cytometry in the mouse aorta and EAhy926 cells using DAF fluorescence intensity. Calcium influx was evaluated in A7r5 cells by flow cytometry. Western blot was used to analyze eNOS and nNOS phosphorylation.

AM reduced PE-induced contraction by calcium influx diminution in smooth muscle cells (F/F0 = 225.6 ± 15.9 and 118.6 ± 17.6 to CT and AM, respectively). AM impaired Ach-dependent vasodilation (Emax = 95.8 ± 1.4; 78.1 ± 1.8; 60.4 ± 2.9 and −7.4 ± 1.0 for CT, 0.01, 0,1 and 1 μmol/L AM, respectively) through reduction of calcium influx and NO availability and TLR4 antagonism in a concentration-dependent manner. AM or TLR4 gene deletion significantly reduced NO production (Fluorescence = 9503 ± 871.7, 2561 ± 282, 4771 ± 728 and 1029 ± 103 to CT, AM, TLR4−/− and AM + TLR4−/−, respectively) by an increase in nNOSser852 and reduction in eNOSser1177 phosphorylation in endothelial cells.

Our data show that amitriptyline impaired vascular function through two different mechanisms: blockade of TLR4 in endothelial cells and consequent decrease in NO production and calcium influx reduction in smooth muscle and endothelial cells. We also suggest, for the first time, nNOS activity reduction by AM in non-neuronal cells.