Direct modulation of secretin binding sites by gastrin in the rat stomach

The effect of gastrin on secretin binding sites in the stomach was studied using the plasma membranes from rat gastric mucosa and vascularly perfused rat stomach. Tetragastrin transiently increased secretin binding to the mucosal plasma membranes. In the perfused stomach secretin binding was also modulated by the inclusion of tetragastrin or human [Leu15] gastrin I in the perfusate. However, histamine did not show such a modulatory effect. Tetragastrin had an insignificant effect on secretin binding sites in rat pancreas. These results suggest that the direct modulation of secretin binding by gastrin to its receptors may be involved in the inhibitory action of secretin on acid secretion induced by gastrin.