The effects of methysergide on the constrictor response to serotonin on the isolated, perfused rabbit ear artery

On the isolated, perfused rabbit ear artery methysergide 10(-9) mol.1(-1) only potentiated the constrictor response to serotonin while at a concentration of 2.5 x 10(-8) mol.1(-1) it only blocked the response. At an intermediate concentration (2.5 x 10(-9) mol.1(-1)) it produced initial potentiation followed by subsequent blockade. In contrast, at all three concentrations it only potentiated the constrictor response to noradrenaline. The results thus show that methysergide can exert a dual effect on the constrictor response to serotonin with the actual effect produced being dependent not only on the concentration of methysergide used but also on the period of time the artery is exposed to methysergide.