The distribution and characterization of somatostatin-like immunoreactivity in epithelial cells, submucosa, and muscle of the rat stomach and intestine.

Abstract

Epithelial cells were isolated by a vibration technique, and the mucosal scrapings of the vibrated gut and muscle layers were prepared from gastric antrum and proximal and distal small intestine and colon of the rat. The tissues were extracted with acid-ethanol, and the somatostatin-like immunoreactivity (SRIF-LI) content was determined by RIA. When expressed as a percentage of the total, the SRIF-LI content of the mucosal epithelial cells isolated by vibration was: antrum, 41%; proximal small intestine, 45%; distal small intestine, 87%; and colon, below the assay detection limit. The mucosal scrapings and muscle layers of these tissues, both areas of dense autonomic innervation, contained the remainder of the SRIF-LI. Chromatography of extracted SRIF-LI from these tissues on Sephadex G-25 superfine, equilibrated and eluted with 0.01 M formic acid, revealed that in the antrum, the SRIF-LI from all layers coeluted with synthetic cyclic tetradecapeptide SRIF (SRIF-14). In the intestine, mucosal cells and scrapings contained principally a large molecular weight form, with an elution volume 70–75% of that between cyanocobalamin and blue dextran. In the muscle layer, two thirds of the SRIF-LI coeluted with SRIF-14, and one third eluted as the large molecular weight form. In the colon, epithelial cells contained principally the large molecular weight form of SRIF-LI; the mucosal scrapings showed an equal distribution between large and SRIF-14 forms, while in the muscle layer, the principal form coeluted with the SRIF-14 standard. These findings suggest that the major molecular form of SRIF-LI in the muscle layers at all levels in the gut is a small polypeptide with an elution volume similar to that of SRIF-14. In the mucosal layer of the antrum, this was also true, whereas in the intestine and colon, a large molecular weight species was found. This may be consistent with different molecular forms of SRIF subserving separate functions in the layers of the gut at various sites.