Interaction of gastrin I and secretin on gastrointestinal circular muscle.

LIPSHUTZ,~ILLIAM, AND SIDNEY COHEN. Interaction of gastrin I and secretin on gastrointestinal circular muscle. Am. J. Physiol. 222(3) : 775-781. 1972.-The effect of gastrin I and secretin was studied on the in vitro circular smooth muscle of the lower esophageal sphincter (LES), antrum, and pylorus of the opossum. Each muscle was studied at its length of optimal tension development, L,, as determined by length-tension diagrams. At Lo, full-dose response curves were constructed for gastrin I and secretin, alone and in combination. Gastrin I stimulated LES and antral muscle, and secretin produced a selective competitive type of antagonism to this gastrin I response. Pyloric circular muscle did not respond to gastrin I. Secretin, over a wide dose range, had little effect on antral and LES muscle. PyIoric circular muscle was stimulated by secretin, and gastrin I produced a selective, noncompetitive type of antagonism to this secretin response. We conclude that the action and interaction of gastrin and secretin on upper gastrointestinal circular smooth muscle differ at each region. It is suggested that these hormonal effects that have been demonstrated in vitro determine, in part, the motor function of these separate anatomic regions in vivo.