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Role of Bombesin in Muscularis Mucosa of Canine Colon

  • F. Angel
  • V. L. W. Go
  • J. H. Szurszewski

Abstract

We have shown previously the presence of a non-cholinergic, non-adrenergic excitatory innervation in the muscularis mucosa of the canine colon. Immunoreactive-like substance P was released in response to nerve stimulation. This release was reduced in the presence of tetrodotoxin and in a calcium-free solution. Bombesin, another peptide present in this muscle, was excitatory when applied exogenously. Excitation with bombesin was blocked by tetrodotoxin. The aims of this study therefore were to determine if bombesin is released during nerve stimulation and if bombesin causes contraction by releasing substance P. Strips of muscularis mucosa were placed in a superfusion apparatus to record contractile activity. Intramural nerves were stimulated by two platinum wire electrodes. The superfusate which passed over each strip was collected and assayed for bombesin-and substance P-like immunoreactivity. Under control conditions, the concentration of bombesin was 6.0 ± 0.9 pg/ml (mean ± SEM). Following nerve stimulation (10 Hz, 10 V, 200 µs) the concentration of bombesin in the superfusate increased significantly (p < 0.02) to 9.41 ± 0.98 pg/ml (mean ± SEM). In the presence of tetrodotoxin (10-6 M) and in a calcium-free bathing solution, the increase in immunoreactive-like bombesin in the superfusate was no longer observed (respectively: 6.37 ± 1.07 pg/m1 and 7.5 ± 1.4 pg/ml). Furthermore, applied bombesin (10-6 M) increased substance P levels (28 ± 1.7 pg/ml) in the superfusate. This increase was reduced significantly (p < 0.05) by tetrodotoxin (11.4 ± 6.5 pg/ml). Finally, with substance P-antiserum in the superfusate (dilution 1:75), the excitatory response induced by either nerve stimulation or exogenous bombesin was decreased. We conclude from these observations that transmural stimulation releases bombesin from intramural nerves and that bombesin acts on substance P-containing nerves to release substance P, thereby causing contraction. (Supported by NIH Grant AM 17238.)

Keywords

Public Health Nerve Stimulation Platinum Wire Press Limited Gastrointestinal Motility 
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Copyright information

© MTP Press Limited 1984

Authors and Affiliations

  • F. Angel
  • V. L. W. Go
  • J. H. Szurszewski

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