THE ACTION OF PHYSOSTIGMINE, DI-ISOPROPYL FLUOROPHOSPHATE AND OTHER PARASYMPATHOMIMETIC DRUGS ON THE RECTUS MUSCLE OF THE FROG

¹ From the Department of Pharmacology Cornell University Medical College

1. The concept that neostigmine, physostigmine, and trimethylamine act directly on skeletal muscle has been explored on the isolated frog rectus abdominis preparation.

2. Muscles immersed for one hour in frog Ringer's solution containing diisopropyl fluorophosphate (DFP) were shown to possess no cholinesterase activity.

3. The response of the frog rectus muscle to acetylcholine was increased after the inactivation of cholinesterase by DFP.

4. Normal muscles and muscles previously treated with DFP were exposed to suitable concentrations of neostigmine, physostigmine and trimethylamine hydrochloride. Each drug produced contraction which was not influenced by DFP. This indicated that these drugs act directly on muscle.

5. In muscles treated with DFP the response to acetylcholine was augmented by a subsequent treatment with physostigmine or neostigmine.