Some studies on peripheral actions of mephenesin, methocarbamol and diazepam.

1. Mephenesin, methocarbamol and diazepam abolished polysynaptic reflex contractions of the cat tibialis anterior muscle elicited by stimulation of the homolateral femoral nerve.2. Mephenesin and methocarbamol caused a prolongation of the mean refractory period of directly or indirectly stimulated skeletal muscle. These effects were due to a direct action on the muscle fibres. There was no effect on responses to single stimuli.3. The increase in refractory period produced by mephenesin was greater in indirectly than in directly stimulated rat diaphragms. Experiments using the isolated phrenic nerve suggest that this difference is due to the local anaesthetic action of mephenesin.4. In the indirectly stimulated cat tibialis anterior muscle high frequency stimulation resulted in a non-maintained tetanus in the presence of mephenesin and methocarbamol.5. Diazepam was without peripheral effects on the responses of skeletal muscle.6. The results with mephenesin and methocarbamol are discussed in relation to their mode of action in reducing muscle spasm.