The effect of insulin on skeletal muscle contractions and its relation to the effect produced by BETA-adrenoceptor stimulation.

The soleus, a slow-contracting, and the extensor digitorum longus (EDL), a fast-contracting muscle, from the guinea-pig were prepared for measurement of isometric contractions in vitro. Insulin, 2.5-55 mu/ml, caused a dose-dependent depression of twitches and subtetanic concentrations of the soleus muscle similar to and additive with that produced by the beta 2-adrenoceptor agonist, terbutaline. The effect of terbutaline but not that of insulin was blocked by propranolol. Insulin had no apparent effect on the contractions of the EDL, whereas terbutaline increased the force of contraction. When depressed by KCl, however, insulin partially restored the twitch tension in both muscles. The possible role of effects on the Na+-K+ transport is discussed.