Relation of gastric acid and pepsin secretion to serum gastrin levels in dogs given bombesin and gastrin-17

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Abstract
To quantitate bombesin stimulation of gastric acid and pepsin via release of gastrin, 5 gastric fistula dogs were given graded doses (60-1250 pmol .cntdot. kg-1 .cntdot. h-1) of bombesin tetradecapeptide and 40-2000 pmol .cntdot. kg-1 .cntdot. h-1 of synthetic gastrin-17 (G-17). Acid and pepsin output and serum gastrin were proportional to the dose of stimulant. The half-maximal dose of bombesin for gastrin release was 200 pmol .cntdot. kg-1 .cntdot. h-1. Bombesin-stimulated acid secretion related to serum gastrin concentrations was congruent with the G-17 curve, but with a maximum of only 62% of the G-17 maximum before declining by 27% despite higher serum gastrin levels. Bombesin probably stimulates acid secretion only via gastrin release and inhibits at higher doses by releasing another inhibitory peptide, most likely somatostatin, which is also released by bombesin. The same mechanism could apply to supramaximal inhibition of acid and pepsin seen with high doses of G-17. Because the pepsin curve related to serum gastrin was to the left of the G-17 curve, another secretagogue released by bombesin apparently acts synergistically with gastrin on pepsin secretion. Therefore, bombesin stimulates gastric secretion through gastrin release, but its effects are modified by peptides coreleased to increase pepsin output at low doses and limit the output of acid and pepsin to 50-60% of the G-17 maximum.