Neuromuscular differentiation of the human pylorus.

The mechanical activity of muscle strips from the gastroduodenal junction as obtained at operations was studied. Strips were cut so as to present the activity of the circular muscle layer of the antrum, the duodenum, the intermediate, or the distal pyloric sphincter. All strips increased and maintained a tension with increasing length, but distal sphincter strips did more so than the other types of strips. Phasic contractions were rare in distal sphincter strips, while all intermediate sphincter strips contracted at rates similar to antral strips. Electric field stimulation produced pure contractions in all responsive strips of the antrum and the intermediate sphincter. In most strips from the duodenum and distal sphincter the contraction response occurred during the stimulus, and the relaxation response far outlasted the stimulus. Distal sphincter strips had the larger relaxation responses, and duodenal strips had the larger contraction responses. Relaxation in response to electric stimulation, Ca++ withdrawal, or isoproterenol did not completely abolish the baseline tension of the distal sphincter. At least in its distal segment, muscle from the human pylorus differs from muscle of the antrum and the duodenum by its high baseline tension, its prominent neurogenic relaxation response, and its poor spontaneous contractile activity.