Comparison of the function of the serotonin transporter in the vasculature of male and female rats.

1. The serotonin transporter (SERT) handles serotonin (5-hydroxytryptamine (5-HT)) and is blocked by the antidepressant SERT inhibitors fluoxetine and fluvoxamine. Although the importance of SERT in the central nervous system is clear, SERT also functions in the peripheral vasculature. In the present study, we tested the hypothesis that the vasculature from female rats has increased SERT function compared with male rats because females are more responsive to SERT inhibitors. 2. In addition to in vitro experiments, in vivo experiments were used to evaluate how male and female rats handle chronically elevated levels of 5-HT. Wild-type (WT) and SERT-knockout (SERT-KO) rats were infused with 5-HT (25 μg/kg per min) for 7 days by minipump. 3. Using HPLC analysis, we demonstrated that blood vessels (aorta, carotid artery, jugular vein and vena cava) from naïve, non-infused female rats took up 5-HT acutely in vitro in a SERT-dependent manner. In in vitro experiments, SERT affected the contractility of aortas from female rats, as evidenced by an eightfold increase in potency of 5-HT in fluvoxamine (1 μmol/L)-incubated WT aortas compared with control. Fluvoxamine did not alter 5-HT-induced contraction in aortas from SERT-KO female rats. 4. Infusion of 5-HT resulted in an increase in tissue 5-HT that was reduced to a larger extent in blood vessels from female than male SERT-KO rats. Aortic contractions to 5-HT were abolished in aortas from male and female 5-HT-infused SERT-KO rats compared with WT rats. 5. Collectively, these data suggest that SERT function, when challenged with 5-HT, is modestly more important in the vasculature of the female compared with male rat.