Differential effect of bombesin on intraluminal and intravascular release of gastric gastrin and somatostatin in anaesthetized rats.

The aim of the present investigation was to study how bombesin, gastrin-17, cholecystokinin-8 (CCK-8) and electrical vagal stimulation influence the release of gastrin and somatostatin into the gastric lumen. Bombesin (3 and 30 nmol kg-1 h-1), gastrin-17 and CCK-8 (10 nmol kg-1h-1) were infused i.v. and vagal stimulations at 5 V, 2 ms, 5 Hz were performed in anaesthetized rats, in which the stomach was perfused with a dextran solution (pH approximately 6 or approximately 1.5). pH, gastrin and somatostatin levels were measured in the perfusate after having passed the stomach. In addition, blood samples were drawn from the jugular vein in the experiments in which bombesin was infused. Gastrin and somatostatin levels were determined with radioimmunoassay, and gastrin- and somatostatin-like immunoreactivity will be referred to as gastrin and somatostatin below. Infusion of bombesin, 3 and 30 nmol kg-1 h-1, did not influence acid secretion as evidenced by an unchanged intraluminal pH. Nor was the intraluminal secretion of gastrin or somatostatin influenced by bombesin, whereas plasma gastrin and somatostatin levels were significantly increased at the higher dose. In contrast, infusion of CCK-8 and gastrin-17 (10 nmol kg-1 h-1), as well as electrical vagal stimulation, significantly decreased the pH and increased the somatostatin levels in the perfusate. Vagal activation in addition increased the gastrin levels. The present results, demonstrating that bombesin influences plasma and perfusate levels of gastrin and somatostatin differently, indicate that intraluminal and intravascular gastrin and somatostatin release may be separately regulated.