Ledda F, Mantelli L
Br J Pharmacol. 1984 Mar;81(3):491-7. doi: 10.1111/j.1476-5381.1984.tb10102.x.
The prejunctional effects of clonidine and phenylephrine were studied in guinea-pig isolated atria by means of field stimulation of the sympathetic nerve terminals during the cardiac refractory period, in the presence of 1 microM atropine. Clonidine (10-100 nM) produced a dose-dependent decrease in the stimulus-inotropic response curve; the IC50 for clonidine was increased about 70 times by the pretreatment of the preparations with 1 microM yohimbine. The effect of clonidine was not modified by 0.5 microM prazosin. Unlike clonidine, phenylephrine (1-10 microM) induced a statistically insignificant increase in the contractile force of preparations stimulated at 4 Hz. The inhibitory effect of phenylephrine (1-10 microM) was partially prevented by either 1 microM yohimbine or 0.5 microM prazosin. However, it was antagonized, to about the same degree as that observed with clonidine, by the pretreatment of the preparations with both 1 microM yohimbine and 0.5 microM prazosin. The results seem to indicate that one component of the prejunctional effects of phenylephrine may be mediated by presynaptic alpha-adrenoceptors belonging to the alpha 1-subtype.
在存在1微摩尔阿托品的情况下，通过在心脏不应期对交感神经末梢进行场刺激，研究了可乐定和去氧肾上腺素对豚鼠离体心房的节前效应。可乐定（10 - 100纳摩尔）使刺激-变力反应曲线呈剂量依赖性下降；用1微摩尔育亨宾预处理标本后，可乐定的半数抑制浓度（IC50）增加约70倍。0.5微摩尔哌唑嗪不改变可乐定的作用。与可乐定不同，去氧肾上腺素（1 - 10微摩尔）对以4赫兹刺激的标本的收缩力产生统计学上无显著意义的增加。1微摩尔育亨宾或0.5微摩尔哌唑嗪可部分阻止去氧肾上腺素（1 - 10微摩尔）的抑制作用。然而，用1微摩尔育亨宾和0.5微摩尔哌唑嗪同时预处理标本后，其拮抗作用与可乐定观察到的拮抗作用程度大致相同。结果似乎表明，去氧肾上腺素节前效应的一个成分可能由属于α1亚型的突触前α肾上腺素能受体介导。
