Kotaro Kaneko

Muscarinic acetylcholine receptors in rat gastric mucosa

SummaryThe muscarinic cholinergic innervation of the rat gastric mucosa was investigated by localizing the muscarinic receptors using a tritiated muscarinic antagonist, pirenzepine. Radioautography was performed by freeze drying stomach tissue, which was then embedded in Epon and wet sectioned with ethylene glycol, and dry mounting on emulsion film by the wire-loop method to prevent loss of the labelled substance during fixation and the radioautographic procedure. Light and electron microscopy showed that the specific pirenzepine-binding sites were localized predominantly on parietal cells, chief cells and perivascular plexuses. Analysis of the grain distribution on parietal cells revealed that the silver grains corresponding to the pirenzepine-binding sites were mainly on the basolateral plasma membrane. On the other hand, the surface mucous or mucous neck cells had few pirenzepine-binding sites.

Autoradiographic demonstration of gastrin-releasing peptide-binding sites in the rat gastric mucosa

The location of [125I]iodotyrosyl gastrin-releasing peptide-binding sites in the rat fundic mucosa was studied. Peptide specificity was demonstrated by competitive binding studies using the addition of a large amount of cold gastrin-releasing peptide or substance P. Autoradiography of the stomach tissue was carried out by freeze-drying, embedding in Epon, wet-sectioning with ethylene glycol, and dry-mounting the emulsion film by the wire-loop method to prevent loss of the labeled substance. Specific binding sites of gastrin-releasing peptide were found on D cells, surface mucus cells, and parietal cells, whereas few binding sites were seen on the chief or mucus neck cells.

Autoradiographic demonstration of gastrin binding sites in rat gastric mucosa.

The location of 125I-iodotyrosyl gastrin I binding sites in rat gastric mucosa was studied. Peptide specificity was demonstrated by competitive binding studies through the addition of a large dose of cold human gastrin I or cholecystokinin-octapeptide. Autoradiography of the stomach tissue was carried out by freeze-drying, embedding in Epon, wet-sectioning with ethylene glycol, and dry-mounting the emulsion film by means of the wire-loop method to prevent loss of the labeled substance. Specific binding sites for gastrin were found on parietal and chief cells, whereas few binding sites were seen on the surface mucous or mucous neck cells. Binding sites on the parietal cells were dispersed in the cytoplasm, while those on the chief cells were found near the basal plasma membrane.

Involvement of autonomic nervous system in gastric mucosal defense mechanism.

This article describes the histochemical, immunohisto-chemical, radioautographic, and ultrastructural localizations of aminergic and peptidergic nerves, neurotransmitter receptors, and their binding sites in the stomach wall. Cholinergic and vasoactive intestinal polypeptide (VIP)-ergic nerve fibers are distributed along the gastric microvasculature, within the myenteric and submucosal plexuses, and in the muscularis mucosae and circular muscle layer. In the mucosa, both nerve fibers evenly extend along the capillaries in association with the epithelial cells up to the mucosal surface. In particular, cholinergic nerves are proved to doubly innervate the mucosal capillaries and nonmuscular venules as well as the parietal cells. Adrenergic and neuropeptide Y (NPY)-containing nerves are distributed primarily along the arterioles of the gastric micro vasculature, within the myenteric plexuses, and in the circular muscle layer. These nerve fibers extend up to the basal portion of the mucosa in close association with small arterioles, capillaries, and epithelial cells. Some of the adrenergic nerve axons are coexistent with the cholinergic nerve axons within the Schwann cell. Histamine H1 receptors are widely located on the walls of arterioles, capillaries and venules, while H2 receptors are evident not only on the parietal cells but also on the walls of the collecting venules and surrounding capillaries in the mucosa. Dopamine D1 receptors are predominantly located on the smooth muscle cells of the arterioles near the muscularis mucosae, while D2 receptors are present on the walls of postcapillary venules and collecting venules. Functional coordination of both intramural peptidergic nerves as intrinsic origin and aminergic nerves as extrinsic origin is considered to be essential for maintaining the gastric mucosal defense mechanism against a variety of aggressive factors.

Fluorescent Histochemical Study on the Localization of Myofibroblasts in the Healing of Acetic Acid-Induced Gastric Ulcers in the Rat

The changes in the localization of FITC-phalloidin-positive smooth muscle cells and interstitial cells were studied in control and acetic acid-treated rat fundic mucosae. In the control rats, the FITC-phalloidin-positive cells mostly corresponded to smooth muscle cells of the muscularis mucosae, and arteriolar and venular smooth muscle cells. On the other hand, the fluorescence of the smooth muscle cells of the muscularis mucosae disappeared and a large number of fluorescent interstitial cells appeared in the regenerated mucosal layer in rats one week after the acetic acid-treatment, while three weeks after the application, severely thickened fluorescent muscularis mucosae were formed.

Alterations in Gastric Mucosal Microvascular Endothelium in a Stressed Condition-Relevance to Gastric Ulcerogenesis

The present paper describes the morphological and functional alterations of the gastric mucosal microvascular endothelium under restraint-stressed condition. On the basis of the direct cholinergic innervation of capillaries and non-muscular venules in the gastric mucosa, these endothelial changes would be caused by the stress-induced overstimulation of the cholinergic nerves and modified by the degranulation of mast cells, contributing to the stress-induced ulcer formation as schematically illustrated in Fig. 10.

Abstracts of selected papers presented at the 30th Annual meeting of the Japanese Society of Gastroenterology

S OF SELECTED PAPERS PRESENTED AT THE 30TH ANNUAL MEETING OF THE JAPANESE SOCIETY OF GASTROENTEROLOGY October 20-22, 1988 -Kagoshima, Japan Chairman: Shuji HASHIMOTO, M.D.

Abnormalities in the Hepatic Sinusoids: Pathological Basis of Self-perpetuation of Liver Cirrhosis

The hepatic microcirculatory system consists of four microvascular components: the terminal portal venule and hepatic arteriole as two afferent vessels, the sinusoids corresponding to the capillary bed, and the terminal hepatic venule as an efferent vessel. This microvascular unit is the basis for the simple liver acinus, which has been proposed as the smallest functional unit of the hepatic lobule [1]. The major components among these microvessels are the hepatic sinusoids, which are characterized by the presence of the sieve-like pores [2], i.e., the sinusoidal endothelial fenestrae (SEF), and by the absence of the basement membrane beneath the sinusoidal endothelial cells. These ultra-structural characteristics reflect the active exchange of metabolites between the sinusoidal blood and the hepatocytes, maintaining constant liver cell functions. In this respect, impairment of the sinusoidal blood flow directly leads to a variety of liver cell dysfunction.

Radioautographic Characterization of H1 and H2 Receptor Antagonists

Histamine is thought to be one of the most important neuromodulators in the gastric mucosa, participating mainly in the regulation of hydrochloric acid secretion and blood flow. Pharmacological studies revealed that the action of histamine is mediated by two types of receptors: H1 and non-H1 receptors, i.e., H2 receptors. The existence of non-H1 receptors was initially revealed through evidence that certain effects of histamine, such as gastric acid secretion and cardiac chronotropism, are not antagonized by typical antihistamines.1 The important derivation of a second class of histamine antagonists2 defined this new class of receptors, the H2 receptors, as being those which are unaffected by classical H2 antihistamines like pyrilamine. The subsequent phenomenal success of this new H2 receptor antagonist, Cimetidine, in treating duodenal ulcers by suppression of acid secretion has confirmed the functional significance of histamine in the gastric mucosa.

Aminergic and Peptidergic Innervation of the Gastric Mucosa—Its Possible Relevance to Ulcerogenesis

A number of studies on the relationship between autonomic nervous abnormalities and gastric ulcer formation were performed since the pioneering reports of Cushing1 and Bergamann.2 However, further investigation of this pathognomonic relationship from a different angle or using a newly developed technique is still warranted in order to clarify the mechanism of gastric ulceration.