摘要：

The enantiomers of clenbuterol, a β2-selective adrenoceptor agonist with partial agonistic activity, were examined with respect to their ability to react in vitro on adrenoceptors in the trachea (mostly β2), the soleus muscle (β<SUB> 2 </SUB>) and in the papillary muscle of the left ventricle (β<SUB> 1 </SUB>) from the guinea-pig. (—)-Clenbuterol relaxed the carbachol contracted trachea and depressed the subtetanic contractions of the soleus muscle in a concentration-dependent manner. (+)-Clenbuterol was at least 1,000 times less potent in this respect. Both isomers inhibited competitively the effect of isoprenaline on the trachea, the (—)-isomer being about 100 times more active than the (+)-isomer. None of the isomers showed any detectable positive inotropic effect on the papillary muscle but both inhibited competitively the response to isoprenaline. Also in this respect (—)-clenbuterol was more potent than (+)-clenbuterol. It is concluded that the β<SUB> 2- </SUB> agonistic as well as the β<SUB> 1 </SUB> -antagonistic effect of clenbuterol resides in the (—)-isomer and that the (+)-isomer does not seem to contribute to the pharmacological effects displayed by racemic clenbuterol.

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