Role of histamine H1- and H2-receptors in myoelectric activity of small bowel in the dog.

Studies were conducted in conscious dogs implanted with monopolar silver electrodes along the small intestine to determine whether the intestinal motility response to histamine is mediated by H1-receptors alone or whether H2-receptors are also involved in the response. Histamine infusion alone induced a marked increase in the appearance rate and the propagation velocity of the interdigestive myoelectric complexes (IMC). This effect was reproduced by the administration of the selective H1-receptor agonist, 2-methylhistamine, and abolished by the H1-receptor antagonist, tripelennamine. Tripelennamine alone decreased the frequency of occurrence of the IMC in fasted animals and reduced significantly the spike potential activity of the small bowel in fed dogs. Neither the H2-receptor agonist, dimaprit, nor the H2-receptor antagonist, metiamide, had any influence on the motility patterns in fasted or fed animals. We conclude that histamine influences the patterns of small bowel motility via stimulation of H1-receptors but its physiological role in modulating intestinal motility remains to be determined.