The response of an isolated artery to sympathomimetic amines

The rabbit ear central artery preparation responded with contractions to noradrenaline, dopamine, tyramine, octopamine, phenylethylamine, β-phenylethanolamine and periarterial sympathetic nerve stimulation. Noradrenaline, dopamine and nervous stimulation gave monophasic responses. Tyramine and octopamine gave biphasic responses consisting of an initial fast contraction followed by a second contraction of slow onset and long duration. Phenylethylamine and phenylethanolamine also gave biphasic responses, but the second contraction was of quick onset and short duration of action and often merged with the first contraction. Cocaine, superior cervical ganglionectomy and reserpinization reduced the second phase of the contraction to tyramine, octopamine and phenylethylamine. The second phase of the response to phenylethanolamine was reduced by reserpine but not by cocaine or denervation.