Torp K D, Tschakovsky M E, Halliwill J R, Minson C T, Joyner M J
Department of Anesthesiology and General Clinical Research Center, Mayo Clinic, Rochester, Minnesota 55905, USA.
J Appl Physiol (1985). 2001 May;90(5):1855-9. doi: 10.1152/jappl.2001.90.5.1855.
Phenylephrine is generally regarded as a "pure" alpha(1)-agonist. However, after treatment of the forearm with the alpha-adrenergic-blocking drug phentolamine, brachial artery infusion of phenylephrine can cause transient forearm vasodilation. To determine whether this response was beta-receptor mediated, phenylephrine, phentolamine, and propranolol were infused into the brachial arteries of six healthy volunteers. Forearm vascular conductance (FVC) was also calculated and expressed as arbitrary units (units). Infusion of phenylephrine by itself (0.5 microg. dl forearm volume(-1). min(-1)) caused a sustained decrease (P < 0.05) in FVC from 3.5 +/- 0.7 to 0.9 +/- 0.2 units (P < 0.05). Infusion of the alpha-blocker phentolamine increased (P < 0.05) baseline FVC to 5.7 +/- 1.3 units. Subsequent infusion of phenylephrine after alpha-blockade caused FVC to increase (P < 0.05) for ~1 min from 5.7 +/- 1.3 to a peak of 13.1 +/- 1.8 units. Propranolol had no effect on baseline flow, and subsequent phenylephrine infusion after alpha- and beta-blockade caused a small, but significant, sustained decrease in FVC from 5.1 +/- 1.0 to 3.6 +/- 0.8 units. There were no systemic effects from the infusions, and saline infusion at the same rate (1-2 ml/min) had no forearm vasoconstrictor or dilator effects. These data indicate that in humans phenylephrine can exert transient beta(2)-vasodilator activity when its predominant alpha-constrictor effects are blocked.
去氧肾上腺素通常被视为一种“纯粹的”α(1)激动剂。然而，在用α肾上腺素能阻断药物酚妥拉明处理前臂后，经肱动脉输注去氧肾上腺素可导致前臂短暂性血管舒张。为了确定这种反应是否由β受体介导，将去氧肾上腺素、酚妥拉明和普萘洛尔输注到6名健康志愿者的肱动脉中。还计算了前臂血管传导率（FVC）并以任意单位（单位）表示。单独输注去氧肾上腺素（0.5微克·前臂体积(-1)·分钟(-1)）导致FVC从3.5±0.7持续下降（P<0.05）至0.9±0.2单位（P<0.05）。输注α受体阻滞剂酚妥拉明使基线FVC增加（P<0.05）至5.7±1.3单位。α受体阻断后随后输注去氧肾上腺素导致FVC在约1分钟内从5.7±1.3增加（P<0.05）至峰值13.1±1.8单位。普萘洛尔对基线血流无影响，在α和β受体阻断后随后输注去氧肾上腺素导致FVC从5.1±1.0持续小幅但显著下降至3.6±0.8单位。输注未产生全身效应，以相同速率（1 - 2毫升/分钟）输注生理盐水对前臂无血管收缩或舒张作用。这些数据表明，在人类中，当去氧肾上腺素主要的α收缩效应被阻断时，它可发挥短暂的β(2)血管舒张活性。
