Ultrastructure of fundus glands of the mouse gastric mucosa

Mucins in Intestinal Mucosal Defense and Inflammation: Learning From Clinical and Experimental Studies

Throughout the gastrointestinal (GI) tract, a distinct mucus layer composed of highly glycosylated proteins called mucins plays an essential role in providing lubrication for the passage of food, participating in cell signaling pathways and protecting the host epithelium from commensal microorganisms and invading pathogens, as well as toxins and other environmental irritants. These mucins can be broadly classified into either secreted gel-forming mucins, those that provide the structural backbone for the mucus barrier, or transmembrane mucins, those that form the glycocalyx layer covering the underlying epithelial cells. Goblet cells dispersed among the intestinal epithelial cells are chiefly responsible for the synthesis and secretion of mucins within the gut and are heavily influenced by interactions with the immune system. Evidence from both clinical and animal studies have indicated that several GI conditions, including inflammatory bowel disease (IBD), colorectal cancer, and numerous enteric infections are accompanied by considerable changes in mucin quality and quantity. These changes include, but are not limited to, impaired goblet cell function, synthesis dysregulation, and altered post-translational modifications. The current review aims to highlight the structural and functional features as well as the production and immunological regulation of mucins and the impact these key elements have within the context of barrier function and host defense in intestinal inflammation.

Localization of histamine and histamine H2-receptor antagonists in the gastric mucosa

Histamine stimulates acid secretion by the parietal cell and this secretion is inhibited by the histamine H2-receptor antagonists. Whole body autoradiography showed that radioactivity from 14C-histamine was localized in the artery walls of the stomach and in the muscularis mucosae, but that the level in the fundic mucosa was the same as the blood. When the H2-receptor antagonists burimamide, metiamide and cimetidine were labelled with 35S, 14C or 3H and dosed to rats, whole body autoradiography showed that the stomach was predominantly labelled in the glandular mucosa from 5 to 120 min after administration. Microautoradiography in the rat and dog after intravenous injection of [3H]metiamide or [3H]cimetidine demonstrated an uptake of tritium in the parietal cell cytoplasm that was 3- to 4-times greater than that found in adjacent peptic cells or areas of muscularis mucosa. The preferential labelling persisted at a low level up to 6h after injection in the rat. The localization of radioactivity from the H2-antagonists in the parietal cell cytoplasm correlates well with their pharmacological activity in preventing acid secretion from this cell.

Effects of secretagogues on oxygen consumption, aminopyrine accumulation and morphology in isolated gastric glands

A recently developed method to isolate gastric glands from the rabbit gastric mucosa (Berglindh and Obrink 1976) was used to study the effects of some common gastric secretagogues. Three parameters were investigated: 1) Respiratory activity; 2) Intraglandular accumulation of the weak base aminopyrine; 3) Quantitative morphology of the parietal cells. The following substances were tested: Histamine, cAMP, db-cAMP, aminophylline, carbachol and pentagastrin. The strongest effect was obtained with db-cAMP which dose-dependently stimulated the respiration up to 200%, increased the aminopyrine accumulation 80% and altered the parietal cell morphology from a typically resting to a typically stimulated state. cAMP also stimulated the respiration but was about 10 times less effective on a molar basis than the dibutyryl form. Histamine, like db-cAMP, stimulated the respiration in a dose-dependent manner and strongly increased the aminopyrine accumulation. The morphological changes were, however, not of the same magnitude as after db-cAMP. Aminophylline, tested only for respiratory activity, stimulated the oxygen consumpation moderately. Carbachol induced a transient increase in both the oxygen consumption and in the aminopyrine accumulation with a peak value after approximately 15 minutes for both, but gave no significant morphological alterations. Pentagastrin, finally, was incapable of inducing changes in any of the three parameters. Aminopyrine was also found to accumulate approx. 50 times in unstimulated, morphologically resting glands. This seems to indicate that there might be acid sites already in resting glands.

Fine structure and possible secretory mechanism of rat palatine glands

Electron microscopic studies of the soft and hard palates of adult male rats, removed before and after stimulation, have been used in the study of possible mechanisms of elaboration and discharge of mucin by the tubuloacinar glands within the palate. Results suggest that both the endoplasmic reticulum and the Golgi apparatus are directly involved in the elaboration of the secretory product.