SOMATOSTATIN (D-) CELLS IN THE RAT PYLORIC ANTRUM, WITH SPECIAL REFERENCE TO THE DESTINATION OF THEIR CYTOPLASMIC PROCESSES

Somatostatin from gastric D-cells exerts inhibitory effects upon acid secretion and gastrin release. From previous morphological investigations, a paracrine mode of action of somatostatin (secretion into the intercellular space) has been postulated. However, the exact route of delivery of gastric somatostatin remains uncertain. To obtain a closer view ofgastric D-cells, their whole shape and their microanatomical relationship were examined in immunostained serial semithin (0.5 μm) sections of the rat pyloric mucous membrane. A minority of D-cells was found to belong to the ‘closed-type’ entero-endocrine cells which showed no contiguity to the luminal surface. The majority of D-cells was of the ‘open-type’. Every D-cell had one (or exceptionally two) basally located and densely immunostained cytoplasmic process which never branched. All these processes regularly extended to capillaries. Only three of fifty D-cells examined were located adjacent to gastrin (G-) cells. Thus, somatostatin may act upon gastric G-cells via a local circulatory system rather than by a paracrine mode of action. Finally, a subpopulation of gastric D-cells was detected which, according to cytological parameters, may also secrete into the gastric lumen. This kind of D-cells seems responsible for the presence of somatostatin in the gastric juice.