Mechanism of the vasoconstrictor action of isoprenaline on an isolated artery preparation

It was not possible to demonstrate a vasodilator action of isoprenaline using the isolated artery segment from the rabbit ear. However, in high doses isoprenaline produced vasoconstriction. This vasoconstrictor response was blocked by α-receptor antagonists but not by β-receptor antagonists, except in high, non-specific doses. The response was not reduced by pretreatment of the rabbits with reserpine or by cocaine. The vasoconstriction produced by isoprenaline in this preparation therefore appears to be due to a direct action on the α-adrenotropic receptors.