Effect of atracurium on twitch, tetanic and post-tetanic twitch responses at the rat neuromuscular junction.

The effect of atracurium on the phenomenon of post-tetanic potentiation, which is believed to be of a presynaptic origin, i.e. due to endogenous transmitter release, was investigated to see if atracurium had a presynaptic inhibitory mechanism at the rat neuromuscular junction. The results showed that atracurium (0.8-80 microM) reduced the indirectly elicited twitch, tetanic and post-tetanic twitch tensions, in a dose-dependent manner. Atracurium (1 microM) produced a tetanic fade in the preparations stimulated at 20 Hz and above. The acetylcholine (ACh) released at high frequencies of nerve stimulation was collected, in the presence of physostigmine (0.77 microM), added to a rat ileum preparation, in which it produced a small contraction which was blocked by atracurium (1 microM), which in turn blocked the contracture produced by ACh (1 microM) added directly to the organ bath. It was concluded that, in addition to its well-known competitive blockade of postsynaptic ACh receptors, atracurium may also have a presynaptic inhibitory effect at the neuromuscular junction.