Anomalous responses to histamine stimulation of guinea-pig oesophageal muscularis mucosae.

The incomplete tachyphylaxis of the contractile response to the H1-stimulants observed on guinea-pig oesophageal muscularis mucosae seems to be H2- and H3-antagonist as well as atropine- and tetrodotoxin-resistant. Lidocaine and eserine partially prevented this process probably by a mechanism independent of their main activity. The dualistic antagonism exerted by mepyramine and methysergide on reproducible histamine responses could be explained by a kinetic condition of "hemi-equilibrium state" together with changes of drug-receptor interaction and by non-specific properties of methysergide. On the whole, the present data indicate that the role of histamine in this tissue has still to be defined.