Inhibition of electrically induced twitch responses of the guinea-pig ileum by histamine.

Inhibition of twitch responses of the guinea-pig isolated ileum to low frequency electric stimulation (0.2 Hz) followed the interpolation of a dose of histamine left in contact for 30 sec. This post-histamine inhibition, which was dose related, was not affected by mepyramine or cimetidine and thus was not brought about by an action on known histamine receptors. Histamine also reduced the height of contractions caused by exogenous acetylcholine (ACh) and this inhibition was quantitatively similar to the degree of post-histamine inhibition of twitch recorded at corresponding times following the removal of histamine by overflow. It therefore seems likely that histamine-induced inhibition of twitch is caused by desensitisation of the postsynaptic membrane to endogenous ACh released during transmural stimulation.