Malta E, McPherson G A, Raper C
Br J Pharmacol. 1979 Feb;65(2):249-56. doi: 10.1111/j.1476-5381.1979.tb07825.x.
1 Activation of pre-junctional alpha-adrenoceptors at the skeletal neuromuscular junction enhances acetylcholine release whereas activation of such receptors at autonomic nerve endings inhibits transmitter output. In the present study the characteristics of pre-junctional alpha-adrenoceptors at motor nerve terminals have been compared with post-junctional (vascular) alpha-adrenoceptors in the cat hind limb.2 Reversal of partial (+)-tubocurarine blockade of contractions of the tibialis anterior muscle was used to monitor pre-junctional activity and increases in hindlimb vascular resistance to assess post-junctional actions at alpha-adrenoceptors.3 Responses to intra-arterial injections of noradrenaline, adrenaline, phenylephrine, oxymetazoline, methoxamine and clonidine were monitored. Dose-response lines for all the compounds except clonidine were parallel. The latter agent produced only weak and inconsistent effects.4 Ratios of the doses of the agents required to produce pre- and post-junctional effects indicated that oxymetazoline and adrenaline possessed some preferential activity at post-junctional sites, whereas the remaining agents were non-selective in their actions. If dose-ratios with respect to noradrenaline were compared at the two sites none of the compounds possessed a marked degree of selectivity.5 In the presence of phentolamine or tolazoline, dose-response curves to the pre- and post-junctional effects of phenylephrine were shifted to a similar extent. Thymoxamine showed preferential activity as a pre-junctional alpha-receptor antagonist.6 In comparing the results of this study with those of other authors, it is apparent that there are marked differences in the characteristics of pre-junctional alpha-receptors at the skeletal neuromuscular junction and at autonomic nerve endings. The pre- and post-junctional alpha-receptors in skeletal muscle show less divergence.
骨骼肌神经肌肉接头处的节前α-肾上腺素能受体激活可增强乙酰胆碱释放，而自主神经末梢处此类受体激活则抑制递质释放。在本研究中，已将猫后肢运动神经末梢节前α-肾上腺素能受体的特性与节后（血管）α-肾上腺素能受体进行了比较。
用部分（+）-筒箭毒碱对胫前肌收缩的阻滞作用的逆转来监测节前活性，并用后肢血管阻力增加来评估α-肾上腺素能受体的节后作用。
监测了动脉内注射去甲肾上腺素、肾上腺素、去氧肾上腺素（苯肾上腺素）、羟甲唑啉、甲氧明和可乐定的反应。除可乐定外，所有化合物的剂量-反应曲线均平行。后者仅产生微弱且不一致的效应。
产生节前和节后效应所需药物剂量的比值表明，羟甲唑啉和肾上腺素在节后部位具有一定的优先活性，而其余药物的作用无选择性。如果比较两个部位相对于去甲肾上腺素的剂量比值，则没有一种化合物具有明显的选择性程度。
在酚妥拉明或妥拉唑啉存在的情况下，去氧肾上腺素（苯肾上腺素）节前和节后效应的剂量-反应曲线以相似程度移位。噻吗洛尔作为节前α-受体拮抗剂表现出优先活性。
将本研究结果与其他作者的结果进行比较时，很明显骨骼肌神经肌肉接头处和自主神经末梢节前α-受体的特性存在显著差异。骨骼肌中的节前和节后α-受体差异较小。
