Effect of 5-hydroxytryptamine-2 and α-adrenergic receptor antagonists on the 5-hydroxytryptamine-induced decrease in rabbit masseter muscle blood flow

A previous study showed a significant decrease in blood flow in the rabbit masseter during infusion of 5-hydroxytryptamine (5-HT) (10−9 mol/l). The aim of the present study was to test the hypothesis that blockade of the 5-HT2 or the α-adrenergic receptor would inhibit the 5-HT-induced decrease of microcirculatory blood flow in the masseter. In 12 rabbits, the masseters were infused with 5-HT (10−9 mol/l) in combination with the α-adrenoceptor antagonist phentolamine (10−6 mol/l) or the 5-HT2-receptor antagonist ritanserin (10−6 mol/l). The effect on microcirculatory blood flow was measured by laser–Doppler flowmetry. Infusion of 5-HT induced a significant decrease in blood flow. Inclusion of ritanserin in the 5-HT infusion solution significantly inhibited this decrease, while inclusion of phentolamine did not. This study therefore showed that the 5-HT2 receptor antagonist ritanserin inhibited the 5-HT-induced decrease in microcirculatory blood flow in the rabbit masseter. This decrease in blood flow is thus mediated by the 5-HT2 receptor.