Sympathomimetic-induced effects in the soleus muscle of the guinea-pig.

Sympathomimetic amines reduced the peak tension, time to peak and time to half-relaxation of indirectly elicited twitches of the guinea-pig soleus muscle in vivo. Clonic contractions of the soleus muscle were depressed by the amines. On a molar basis salbutamol and orciprenaline were 5.12 and 80.0 times less potent than (+/-)-isoprenaline in producing these effects. Results obtained with the beta-receptor antagonists propranolol, practolol and H35/25 suggest that the depression in skeletal muscle contractility is due to beta2-adrenoreceptor stimulation. The effects of the amines on twitches and clonic contractions of the guinea-pig soleus muscle are qualitatively similar to those reported previously in the cat soleus muscle preparation, which has been used to assess the possible tremorogenic actions of sympathomimetic bronchodilators. On a quantitative basis the molar dose-ratios of the sympathomimetics used, and the effects of beta-receptor antagonists on the responses, are similar in the two species.