Relative pre- and postjunctional effects of a new vecuronium analogue, Org 9426, at the rat neuromuscular junction.

We have studied the relative pre- and postjunctional neuromuscular blocking effects of Org 9426 in the isolated rat hemidiaphragm muscle using twitch tension and electrophysiological recording techniques. Postjunctional effects were assessed from decreases in twitch height and from end-plate current amplitude and time constant of decay. Prejunctional effects were assessed from the fade of tetanic twitch tension and end-plate current amplitude rundown. There were no significant differences between the relative pre- and postjunctional effects of Org 9426 and those of previously studied steroidal neuromuscular blocking compounds. It is concluded, therefore, that the rapid onset and short duration of Org 9426 seen in vivo is not a consequence of a strong prejunctional, relative to postjunctional, blocking effect of the compound.