Lee T J, Araki H, Su C
J Cardiovasc Pharmacol. 1981 Sep-Oct;3(5):965-76. doi: 10.1097/00005344-198109000-00006.
This study examined in vitro tyramine (TY)-induced contractions of the isolated ring segments of the rabbit basilar and ear arteries in relation to their sympathetic innervations. The TY dose--response relationship in the basilar artery was not affected by cocaine, chronic sympathectomy, or reserpine pretreatment. However, these treatments shifted the TY dose--response relationship in the ear arteries significantly to the right. These results indicate that the TY-induced contraction in the basilar artery is due solely to its direct stimulation of the postsynaptic alpha-receptors, but in the ear artery it is due both to its indirect [release of norepinephrine (NE)] and direct actions. The failure of TY to induce contraction in the basilar artery by the indirect mechanism is probably in part due to a wide synaptic cleft distance and the reported insensitivity of alpha-receptors of this artery. These results suggest that the endogenous NE releasable from the sympathetic nerve in the basilar artery is insufficient to bring about vasoconstriction. This is turn favors our previous hypothesis that transmural-nerve-stimulation (TNS)-induced constriction of this artery is to a transmitter other than NE. It further suggests that the functional significance of the sympathetic innervations to different regions of the vessels is highly variable even when they are of the same ganglionic origin.
本研究检测了酪胺（TY）在体外对兔基底动脉和耳动脉分离环段的收缩作用，并探讨了其与交感神经支配的关系。基底动脉中TY的剂量-反应关系不受可卡因、慢性交感神经切除术或利血平预处理的影响。然而，这些处理使耳动脉中TY的剂量-反应关系显著右移。这些结果表明，基底动脉中TY诱导的收缩完全是由于其对突触后α受体的直接刺激，但在耳动脉中，它是由于其间接作用（去甲肾上腺素（NE）的释放）和直接作用。TY不能通过间接机制在基底动脉中诱导收缩，可能部分原因是突触间隙距离较宽以及该动脉α受体不敏感的报道。这些结果表明，基底动脉中交感神经释放的内源性NE不足以引起血管收缩。这反过来支持了我们之前的假设，即透壁神经刺激（TNS）诱导的该动脉收缩是由NE以外的递质介导的。这进一步表明，即使交感神经支配的血管起源于同一神经节，其对血管不同区域的功能意义也存在很大差异。
