β₁-Adrenoceptor-Mediated Relaxation by Norepinephrine in Dog Hepatic Arteries

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Dog hepatic arterial strips treated with prazosin responded to norepinephrine with concentration-related, endothelium-independent relaxations, the maximal response being 81.7% of the papaverineinduced maximal relaxation that was markedly greater than that in renal arteries. The norepinephrineinduced relaxation in hepatic arteries was significantly attenuated by metoprolol but not influenced by butoxamine. Relaxant responses to norepinephrine of dog hepatic arteries appear to be mediated by the β₁-adrenoceptor subtype, like those of coronary arteries. Evidence for functioning of the β₁-subtype in hepatic arteries would contribute to the analysis of neural and hormonal regulation of blood flow in the liver.