Bombesin--the most stimulating peptide of human gastric smooth muscle.

The mechanical activity of isolated muscle strips from different regions of 33 human stomachs was measured under auxotonic conditions. After application of bombesin (stepwise increases in organ bath concentrations 10(-9) to 10(-6) mol/l) the following in vitro effects were observed in human gastric muscle: (1) Bombesin stimulated both circular and longitudinal preparations from all regions of the human stomach and circular duodenum. (2) The quality of the responses to bombesin application was dependent on the general myogenic characteristics of the preparations of the different stomach regions. The contraction pattern changed at high bombesin concentrations in the organ bath to slower fluctuations. (3) Bombesin resulted in a maximal tonic response in the pyloric region preparations. An increase in tone was usually observed in the inner pyloric preparations, being typical for the region. (4) The effects of bombesin on the human stomach were stronger than the effects of many other regulatory peptides and of the reaction to acetylcholine. (5) The bombesin-induced effects were unaltered by pretreatment with atropine or TTX. (6) The response to bombesin frequently lasted for hours after washing before reassuming the original state.