Predominant sensitivity to tyramine in the isolated intermediate auricular artery of the dog

Using a steel cannula inserting method, the action of tyramine on segments of similar size from isolated intermediate auricular and mesenteric arteries of the dog was investigated. In intermediate auricular arteries, intra-luminally administered tyramine caused strong vasoconstriction, i.e. the threshold dose for inducing constriction was about 0.03 to 0.1 micrograms and at a dose of 3 micrograms the tyramine-induced increase in perfusion pressure was usually more than 200 mm Hg. On the other hand, in mesenteric arteries, tyramine caused only a small increase in perfusion pressure, i.e. the threshold dose was about 1 to 3 micrograms and the maximum level of the increase in perfusion pressure was only 15 to 30 mm Hg even at the large dose of 100 micrograms. The tyramine-induced constriction was blocked by pretreatment with imipramine. Potassium chloride-induced constriction was not inhibited by imipramine in doses which markedly suppressed tyramine-induced responses. Imipramine failed to potentiate the effects of noradrenaline but rather suppressed them in a dose-related manner in both arteries. In intermediate auricular arteries from reserpine-pretreated dogs, the effect of tyramine was attenuated whilst that of noradrenaline was significantly enhanced. Both arterial preparations responded well to periarterial electrical nerve stimulation but at lower stimulus frequencies, intermediate auricular arteries were more responsive than mesenteric arteries. It is suggested that the intermediate auricular artery of the dog has predominant sensitivity to intraluminally administered tyramine which may be related to the role of this vessel in the regulation of cutaneous blood flow.