Morphology of the canine pyloric sphincter in relation to function

Abstract

The ultrastructure and immunocytochemistry of the canine distal pyloric muscle loop, the pyloric sphincter, were studied. Cells in this muscle were connected by gap junctions, fewer than in the antrum or corpus. The sphincter had a dense innervation and a sparse population of interstitial cells of Cajal. Most such cells were of the circular muscle type but a few were of the type in the myenteric plexus. Nerves were sometimes associated with interstitial cell profiles, but most nerves were neither close to nor associated with interstitial cells nor close to smooth muscle cells. Nerve profiles were characterized by an unusually high proportion of varicosities with a majority or a high proportion of large granular vesicles. Many of these were shown to contain material immunoreactive for vasoactive intestinal polypeptide (VIP) and some had substance P (SP) immunoreactive material. All were presumed to be peptidergic. VIP was present in a higher concentration in this muscle than in adjacent antral or duodenal circular muscle. Interstitial cells of Cajal made gap junctions to smooth muscle and to one another and might provide myogenic pacemaking activity for this muscle, but there was no evidence of a close or special relationship between nerves with VIP or SP and these cells. The absence of close relationships between nerves and either interstitial cells or smooth muscle cells leaves unanswered questions about the structural basis for previous observations of discrete excitatory responses or pyloric sphincter to single stimuli or nerves up to one per second. In conclusion, the structural observations suggest that this muscle has special neural and myogenic control systems and that interstitial cells may function to control myogenic activity of this muscle but not to mediate neural signals.

Ultrastructural identification of the c-kit- expressing interstitial cells in the rat stomach: a comparison of control and Ws/Ws mutant rats

“…On the other hand, the second type of cell in the present study probably corresponds to fibroblast-like ICC (Daniel et al 1989) and shows close similarities to fibroblast-like cells in the DMP region of the guinea-pig small intestine (Zhou and Komuro 1992a, b) and the rat small intestine , although their gap junctions seem to be larger in size and number than those of the small intestine.…”

“…Therefore, it can be concluded that the first cell type, which is characterized by large gap junctions, abundant mitochondria, and a highly electron-dense cytoplasm conforms to ICC in the rat stomach, as previously suggested by evidence that ICC in the mouse small intestine express c-kit mRNA (Huizinga et al 1995) and that the myenteric ICC of the guinea-pig small intestine show immunoreactivity to anti-c-kit receptors . This first type of interstitial cell in the rat stomach appears to correspond to ICC of the dog stomach, which are described as having an electron-dense cytoplasm (Daniel et al 1984(Daniel et al , 1989, and also to ICC of the human stomach, which are characterized by abundant intermediate filaments (Faussone-Pellegrini et al 1989). …”

Immunohistochemical identification of cholecystokinin A receptors on interstitial cells of Cajal, smooth muscle, and enteric neurons in rat pylorus

“…In addition, CCKAR-bearing ICC were located in two bands of circular muscle of terminal antrum origin, that rotated near the midventral and dorsal sides of the pylorus to join the sphincter muscle. These latter two bands of circular muscle could be regarded as the equivalent to the inner muscle loops in the guinea pig, which change direction to join the distal sphincter muscle (Cai and Gabella 1984) and the torus described in dogs and humans (Torgensen 1942;Schulze-Delrieu et al 1984;Daniel et al 1989). Thus, CCKAR-bearing ICC are limited to a specific region of the distal pyloric sphincter, where fibers of antral and duodenal origin fuse.…”

Muscular architecture and VIP-like immunoreactive nerves in the gastroduodenal junction of the chicken

“…As regards its role as a muscle relaxant, there are many in vivo studies on the inhibitory actions of VIP on sphincters (for review, see Daniel, 1985). Indeed, a dense distribution of VIP-like imrnunoreactive nerves has been found in the sphincters of the gastrointestinal tracts of various mammals Daniel et aL, 1989;Gonda et aL, 1989). The dense distribution of VIP-like immunoreactive nerve fibres in the inner part of the inner muscle layer in the pyloric part tends to suggest that the ventriculopyloric orifice and the pyloric part itself constrict with a sphincter-like action and that the inner part of the inner muscle layer is the main contributor to this contraction.…”

“…Indeed, numerous nerves with VIP-like immunoreactivity have been found in such sphincters Gonda et aL, 1989;Daniel et al, 1989). Many authors have examined the distribution of the VIP-like immunoreactive nerves in the gastrointestinal tract of birds (Sundler et al, 1979;Vaillant et aL, 1980;Fontaine-Perus et aL, 1981;Reinecke et aL, 1981_;Saffrey et aL, 1982;Epstein et al, 1983;Vittoria et al, 1992).…”