Myogenic basis of motility in the pyloric region of human and canine stomachs.

In vitro gastric motility was investigated in 48 human and 16 canine stomachs by measuring the mechanical activity of isolated muscle strips under auxotonic conditions. For a precise regional differentiation, we recorded the mechanical activity of longitudinal and circular strips from fundus, corpus and antrum, as well as from circular preparations of the inner and outer layer of the pyloric sphincter and from the duodenum. The analysis showed that the anatomical division of the stomach into three distinct regions resulted physiologically in different patterns of contraction in vitro for each region. The fundus exhibited purely tonic spontaneous activity and a tonic contraction pattern after application of acetylcholine whereas the activity in the circular antrum was purely phasic. A combination of tonic and phasic contractions was found in the corpus and longitudinal antrum. A major difference in the basic spontaneous activity pattern was evident between man and dog. A gradient of intrinsic frequency in the stomach from proximal to distal was seen in the dog but not in man. A physiologically distinct area exists in the pyloric region of both species adjacent to the antrum and duodenum. The pyloric ring has its own spontaneous activity (minute-rhythm), reacts to the application of acetylcholine with relatively weak contractions and, unique to the dog, was delineated by histamine-induced maximal contractions. The results provide evidence that the pyloric ring is a distinct organ with specific functional characteristics in its cellular-myogenic structure.