Abstract
The action of pyridine-2-aldoxime methochloride (PAM) was evaluated on nerve–muscle preparations in vitro and in situ. On the isolated diaphragm of the rat, PAM shows a d-tubocurarine-like effect at concentrations higher than 6 mM. No facilitating effects were observed with lower concentrations, even when the acetylcholinesterases were inhibited to an important extent. However, the biphasic actions of PAM could be demonstrated with nerve–muscle preparations of the rat and rabbit in situ: lower concentrations produced fasciculations and twitch potentiation whereas a depressing d-tubocurarine-like effect was obtained with higher doses. The decrease in the amplitude of contraction appears to be related to an action at the myoneural junction rather than a direct toxic action on the muscle fibers themselves.

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