Studies on 5-hydroxytryptamine receptors on isolated human femoral veins and arteries and the influence of dihydroergotamine.

5-Hydroxytryptamine (5-HT) caused concentration-dependent contractions in human postmortem femoral venous and arterial strips. In veins, it was a more potent agonist than noradrenaline, while the reverse was true for arteries. Pizotifen and methysergide were competitive antagonists against 5-HT in femoral arteries with pA2 values of 8.18 and 8.37, while in femoral veins they exerted noncompetitive antagonism. Dihydroergotamine (DHE) antagonized the 5-HT effect in a manner which was not competitive both in veins and arteries. At concentrations employed in antagonist experiments, it increased the resting tone, particularly in veins. The contractile response of veins to DHE was inhibited when the vascular preparations were preincubated with pizotifen at nanomolar concentrations. The results suggest that 5-HT receptors on veins differ from those on arteries. DHE possesses comparatively high affinity for 5-HT receptors on veins. It is concluded that 5-HT receptors may be involved in the contractile response of veins to DHE.