The effects of a beta-2 selective adrenergic receptor antagonist (ICI 118,551) on twitch tension in cat soleus muscle.

We examined the interaction between isoproterenol and erythro-dl-1-(7-methylindan-4-yloxy)-3-isopropylaminobutan-2-ol (ICI 118,551), a beta-2 selective adrenergic receptor antagonist, with respect to heart rate, diastolic blood pressure and twitch tension (soleus muscle) in anesthetized cats. Dose-response curves to isoproterenol (0.025-1.0 micrograms/kg i.v.) were generated for each parameter and then repeated successively after three doses of ICI 118,551 (10, 25 and 100 micrograms/kg i.v.) ICI 118,551 did not significantly alter isoproterenol-induced changes in heart rate, but effects on diastolic blood pressure and twitch tension were inhibited competitively. The data confirm the beta-2 nature of the skeletal muscle adrenergic receptor and suggest that it may be slightly more sensitive than that in blood vessels. Because depression of twitch tension is known to correlate with essential tremor, the data are consistent with clinical reports demonstrating control of tremor by nonselective beta adrenergic receptor antagonists. ICI 118,551 may be efficacious in controlling tremor in man.