COMPARISON OF THE EFFECTS OF HISTAMINE AND N-ALPHA-METHYLHISTAMINE ONNEURONAL FUNCTION IN THE GUINEA-PIG ESOPHAGUS AND ILEUM

The effects of histamine and N-alpha-methylhistamine, two components o f gastric juice, on vagal and transmural stimulation of the guinea-pig isolated oesophagus were compared with their effects on cholinergic a nd on nonadrenergic-non-cholinergic (NANC) neuronal responses in the i solated ileum, both tissues having been pretreated with mepyramine (1 mu M). Histamine (less than or equal to 10 mu M) and N-alpha-methylhis tamine (less than or equal to 1 mu M) had no significant effect on eit her vagal or transmural stimulation in the oesophagus. Substance P, wh ich produces a contraction by activation of cholinergic nerves in the oesophagus also was unaffected by histamine. In contrast, the agonists inhibited contractions produced by cholinergic nerve stimulation in t he ileum; the inhibition produced by histamine (10 mu M) was up to 73 +/- 5%, that by N-alpha-methylhistamine (1 mu M), 48 +/- 5%. Histamine also inhibited responses to stimulation of NANC neurons by up to 37 /- 14%. The effects of histamine and N-alpha-methylhistamine in the il eum were inhibited by clobenpropit (0.1 mu M). These findings suggest that histamine and N-alpha-methylhistamine have no role in the modulat ion of neuronal function in the oesophagus, in contrast with their eff ect in the ileum.