[Effect of arotinolol on the incomplete tetanic contractions of the cat soleus muscle--relation to its anti-tremorgenic action].

The effect of arotinolol on the incomplete tetanic contractions of the cat soleus muscle was studied. Isoproterenol and epinephrine injected intravenously decreased the tension and degree of fusion of incomplete tetanic contractions of the soleus muscle in anesthetized cats. Intravenous arotinolol (> 3 micrograms/kg), propranolol (> 30 micrograms/kg) and pindolol (> 3 micrograms/kg) blocked the effects of isoproterenol and epinephrine, but atenolol (-300 micrograms/kg), prazosin (0.1-10 micrograms/kg) and phentolamine (10, 30 micrograms/kg) did not block them. These results indicate that the receptors involved can be classified as of the beta 2-type. It is proposed that arotinolol may inhibit beta 2-adrenoceptors in the extrafusal muscle fibers of slow muscle, and thereby reduces the amplitude of tremor by changing the incomplete tetanic contractions of the muscle to the complete ones.