Facilitation of neuromuscular transmission by anticholinesterase drugs

THE EFFECTS OF PHYSOSTIGMINE ON THE MECHANICAL AND ELECTRICAL RESPONSES OF THE CAT NICTATING MEMBRANE

The effects of physostigmine on the electrical and mechanical responses of the nictitating membrane elicited by single nerve shocks have been studied in cats anaesthetized with a mixture of chloralose and pentobarbitone. The results were variable but the most consistent effect, observed with large doses of physostigmine, was a depression and prolongation of the contractions which was sometimes associated with augmentation of the characteristic rhythmic electrical activity of the smooth muscle. Although the amplitude of single responses was depressed, incomplete tetanic contractions were sometimes increased in tension because of the greater fusion which occurred as a result of prolongation of the units of contraction. Possible mechanisms underlying the effect of physostigmine are discussed.

A quantitative comparison of the antagonism of tubocurarine and diallylnortoxiferine by four anticurare agents

The antagonism of tubocurarine and diallylnortoxiferine by neostigmine, physostigmine, edrophonium and ambenonium, has been examined on the rat phrenic nerve diaphragm preparation. Ambenonium showed the greatest activity and physostigmine and edrophonium were the least potent and equally active. This order applied to both neuromuscular blocking agents, but all four antagonists show significantly greater activity against diallylnortoxiferine. The possibility that neostigmine and physostigmine have some qualitative differences in anticurare mechanism compared with edrophonium and ambenonium, on this preparation, is discussed.