COMPARISON OF THE EFFECTS OF PANCURONIUM AND TUBOCURARINE ON DIFFERENT MUSCLES OF YOUNG AND OLD MICE

In order to evaluate the sensitivity of different muscle typesto neuromuscular blocking drugs, a system using mouse musclesin vitro was developed and applied to detect changes in drugsensitivity in relation to age. The effect of pancuronium andtubocurarine on initial twitch and on the ratio of fourth twitchto first twitch (T4/T1) of a train-of-four at 2 Hz were comparedin fast-twitch, slow-twitch and respiratory muscles in the mouse.The muscles used were: extensor digitorum longus (EDL), soleus(SOL) and diaphragm (DIA). For both drugs the order of decreasingsensitivity was EDL > SOL > DIA. This result was the samewhether first twitch or T4/T1 was used, although the latterwas a more sensitive indicator. The sensitivity of neuromuscularblock was less in muscles from old (30–33 month) animalsthan in the equivalent muscles from young (8–12 month)animals.