Sarpogrelate Dilates Cerebral Arteries in the Absence of Exogenous Serotonin

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Vasoconstriction of arteries induced by serotonin (5-hydroxytryptamine: 5-HT) is mediated by 5-HT2A and 5-HT1B receptors localized on smooth muscle. The present study investigated the impact of sarpogrelate, a 5-HT2A receptor antagonist, on cerebral artery diameter in the presence and absence of exogenous 5-HT. Diameter measurements were obtained in vitro from rabbit cerebral arteries pressurized to 60 mmHg. In the absence of 5-HT, arteries exhibiting pressure-induced myogenic tone dilated to sarpogrelate in a concentration-dependent manner (half maximal inhibitory concentration [IC50] ≈ 2.3 μM). In a separate experimental series, exogenous application of 5-HT (0.01 μM) caused further constriction of myogenically active arteries, decreasing cerebral artery diameter by an additional 25%. In the presence of 5-HT, sarpogrelate caused concentration-dependent vasodilation (IC50 ≈ 2.3 μM) that was similar to that observed in the absence of exogenous 5-HT. Dilation induced by sarpogrelate was not affected by physical removal of the endothelium or inhibition of nitric oxide synthase with Nω-nitro L-arginine. The highest concentration of sarpogrelate (100 μM) induced near maximal dilation, comparable to dilation induced by the L-type voltage-dependent calcium channel antagonist diltiazem. These findings suggest that in rabbit cerebral arteries, sarpogrelate has direct vasodilator effects on vascular smooth muscle.