Chronic treatment with fluoxetine modulates vascular adrenergic responses by inhibition of pre- and post-synaptic mechanisms

Fluoxetine, a serotonin reuptake inhibitor (SSRI), has other effects in addition to blocking serotonin reuptake, including changes in the vasomotor tone. Whereas many studies focused on the acute effects of fluoxetine in the vasculature, its chronic effects are still limited. In the present study, we tested the hypothesis that chronic fluoxetine treatment modulates adrenergic vascular responses by interfering with post- and pre-synaptic mechanisms. Wistar rats were treated with vehicle (water) or chronic fluoxetine (10 mg/kg/day) for 21 days. Blood pressure (BP) and heart rate were measured. Vascular reactivity was evaluated in perfused mesenteric arterial beds (MAB) and in mesenteric resistance arteries. Protein expression by western blot analysis or immunohistochemistry, β-arrestin recruitment by BRET and calcium influx by FLIPR assay. Fluoxetine treatment decreased phenylephrine (PE)-induced, but not electrical-field stimulation (EFS)-induced vasoconstriction. Fluoxetine-treated rats exhibited increased KCl-induced vasoconstriction, which was abolished by prazosin. Desipramine, an inhibitor of norepinephrine (NA) reuptake, increased EFS-induced vasoconstrictor response in vehicle-treated, but not in fluoxetine-treated rats. Chronic treatment did not alter vascular expression of α1 adrenoceptor, phosphorylation of PKCα or ERK 1/2 and RhoA. On the other hand, vascular contractions to calcium (Ca2+) as well as Ca2+ influx in mesenteric arteries were increased, while intracellular Ca2+ storage was decreased by the chronic treatment with fluoxetine. In vitro, fluoxetine decreased vascular contractions to PE, EFS and Ca2+, but did not change β-arrestin activity. In conclusion, chronic treatment with fluoxetine decreases sympathetic-mediated vascular responses by mechanisms that involve inhibition of NA release/reuptake and decreased Ca2+ stores.