The Role of Alpha-Adrenoceptor Subtype on Microvessels

血管平滑肌对α-AR介导的血管收缩的高反应性已被认为是高血压状态下维持血管阻力升高的一个因素。α-AR收缩可以由两种类型的α-AR α-1和α-2介导。在高血压大鼠（SHR）外周血管阻力的维持过程中，α-AR的哪一种亚型起主要作用尚没有确切的证据。用离体视频显微镜观察了自发性高血压大鼠（SHR）高血压前期（4-5周）和高血压早期（7-8周）阻力大动脉α-肾上腺素受体（α-AR）的敏感性。在组织浴中用玻璃微量移液管对显微切割的血管进行双重插管。在哌唑嗪或萝芙木碱存在下获得去甲肾上腺素（NE）浓度-反应曲线，以确定选择性刺激α-1或α-2 AR所需的NE浓度。在两个阶段，SHR对α 1收缩的敏感性均显著高于WKY。SHR和WKY的α 2收缩无差异。我们还研究了哪种α亚型对SHR的肌源性调节具有更大的敏感性。在管腔内压力期间，α-2期间的肌源性收缩大于α-1。提示α AR对血管收缩的敏感性在高血压血管阻力升高的维持或病因中起作用。

Hyperresponsiveness of vascular smooth muscle to alpha-AR-mediated vasoconstriction has been proposed as a factor involved in maintenance of the elevated vascular resistance in hypertensive state. alpha AR constriction can be mediated by two types of alpha-AR, alpha-1 and alpha-2. No conclusive evidence has been demonstrate in which subtype of alpha-AR playesmainly the role on maintenance of peripheral resistance in hypertensive rats (SHR). The sensitivity of alpha-AR of resistance large arteriole was examined with in vitro videomicroscopy in prehypertensive(4-5 week) and early hypertensive stage(7-8 week) of SHR compared with age mayched WKY. Microdissected vessels were double-cannulated with glass micropipets in a tissue bath. Norepinephrine (NE) concentration-response curves were obtained in the presence of prazosine or rauwolscine to establish the concentrations of NE required to selectivity stimulate alpha-1 or alpha-2 AR. The sensitivity to alpha-1 constriction was much greater in SHR than WKY in both stage. There was no difference in alpha-2 constriction between SHR and WKY. We also examined to explore which alpha subtype has a greater sensitivity to myogenic modulation in SHR. Myogenic constriction during in lumen pressure was greater during alpha-2 than alpha-1. These finding suggested that hypersensitivity of alphaAR to vasoconstriction play a role on maintenance or etiologic factor in elevated vascular resistance in hypertension.