Differences in adrenergic nerve and receptor function in dog internal thoracic, coronary and mesenteric arteries

Isolated dog internal thoracic arteries (ITA) responded to norepinephrine and phenylephrine with concentration-related contractions, which were suppressed by prazosin, but not by yohimbine. Clonidine did not contract ITA. In coronary arterial strips, norepinephrine produced a relaxation. Isoproterenol relaxed coronary arterial strips contracted with serotonin but did not alter the tone of ITA. Forskolin and beraprost, an analog of prostaglandin I2, relaxed coronary and ITA strips to a similar extent. The beta-adrenoceptor density, assayed by [3H]dihydroalprenolol binding, was markedly less in ITA than in coronary arteries. Nicotine and transmural electrical stimulation did not alter the tension of ITA. Immunohistochemical study indicated that nerve fibers containing tyrosine hydroxylase immunoreactivity were markedly less in ITA than in coronary and mesenteric arteries. These results indicate that beta-adrenoceptor function and adrenergic innervation are considerably reduced in dog ITA. Norepinephrine-induced vasocontraction appears to be mediated by alpha 1-adrenoceptors in the arteries.