Stimulation of canine pancreatic polypeptide, gastrin, and gastric acid secretion by ranatensin, litorin, bombesin nonapeptide and substance P.

Four dogs with chronic gastric fistulas were give intravenous bombesin nonapeptide (B9), ranatensin, and litorin by constant infusion for 90 min at 1.2 micrograms x kg-1 on separate days. A dose response study with substance P (1.5, 3.0, 60, 18 and 54 micrograms x kg-1 x h-1) was also carried out and all tests compared to a standard protein meal (10g x kg-1). Plasma gastrin and PP were measured by radioimmunoassay and gastric acid by autobiuret titration. Substance P failed to stimulate gastric acid secretion or release either pancreatic polypeptide (PP) or gastrin. Basal gastrin levels were 8 +/-2 fmol/ml. The peak increment of gastrin released by bombesin was 95 +/- 16, ranatensin 22 +/- 6, litorin 18 +/- 4, and meal 39 +/- 5 fmol/ml. Bombesin caused significantly greater release of gastrin than a meal, litorin or ranatensin (P less than 0.01). Basal gastric secretion was 23 +/- 4 microequiv./min. B9 produced a peak acid secretion of 356 +/- 124 muequiv./min. There was no significant difference between the bombesin-like peptides (P less than 0.01). Basal plasma PP was 38 +/- 12 fmol/ml. B9 produced a peak PP increment of 600 +/- 50, litorin 137 +/- 36, ranatensin 98 +/- 11, and a meal 305 +/- 58 fmol/ml. B9 released significantly more PP than either litorin of ranatensin (P less than 0.01). The different amino acid sequences of the peptides are probably responsible for their potency. The substitution of a penultimate phenylalanine residue in litorin and ranatensin for leucine in bombesin does not prevent PP or gastrin release by bombesin-like peptides. Since bombesin-like peptides are widely distributed in the gastrointestinal tract of man and stimulate both acid and gut hormone secretion, it is possible that they might play a physiological role in the modulation of gastrointestinal function.