Comparison of the Effects of Histamine and Nα-Methylhistamine on Neuronal Function in the Guinea-pig Oesophagus and Ileum

Abstract

Abstract The effects of histamine and Nα-methylhistamine, two components of gastric juice, on vagal and transmural stimulation of the guinea-pig isolated oesophagus were compared with their effects on cholinergic and on non-adrenergic-non-cholinergic (NANC) neuronal responses in the isolated ileum, both tissues having been pretreated with mepyramine (1 μm). Histamine (≤10 μm) and Nα-methylhistamine (≤1 μm) had no significant effect on either vagal or transmural stimulation in the oesophagus. Substance P, which 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 the ileum; the inhibition produced by histamine (10 μm) was up to 73 ± 5%, that by Nα-methylhistamine (1 μm), 48 ± 5%. Histamine also inhibited responses to stimulation of NANC neurons by up to 37 ± 14%. The effects of histamine and Nα-methylhistamine in the ileum were inhibited by clobenpropit (01 μm). These findings suggest that histamine and Nα-methylhistamine have no role in the modulation of neuronal function in the oesophagus, in contrast with their effect in the ileum.