Pharmacological actions of a new -adrenoceptor agonist, MJ-9184-1, in anaesthetized cats

1. The effects of (-)-isoprenaline and the new beta-adrenoceptor agonist, MJ-9184-1, on the lungs, on the cardiovascular system, and on slow contracting skeletal muscle have been compared in cats under chloralose anaesthesia.2. Both amines reduced the increases in airways resistance produced by 5-HT, depressed incomplete tetanic contractions of the soleus muscle, lowered the blood pressure and produced an increase in heart rate. In comparison with (-)-isoprenaline, MJ-9184-1 had a long duration of action.3. The effects of MJ-9184-1 and (-)-isoprenaline were antagonized by the beta-adrenoceptor antagonist, propranolol.4. MJ-9184-1 was approximately half as potent as (-)-isoprenaline in its effects on pulmonary resistance and soleus muscle contractility, and one seventh as potent in producing chronotropic effects in the heart.5. These results suggest that MJ-9184-1 possesses some specificity as a beta(2) receptor stimulant.