Abstract

The antagonism of iproniazid, harmaline, pargyline, tranylcypromine and pheniprazine against the actions of norepinephrine, acetylcholine and potassium has been studied in the isolated medial smooth muscle of the nictitating membrane of the cat. The tension-response characteristics of the preparation were determined and it was established that repeated dose-response curves in a single preparation were very consistent. All five MAO inhibitors caused a marked antagonism of norepinephrine which was characterized by depression of the maximum respones. The antagonism against acetylcholine was very similar. Potassium was also antagonized, although maximum responses could not be determined. There was no evidence for specific blockade of norepinephrine in preference to the other two agonists. It is concluded that the antagonism is noncompetitive.