Gerald P. Morris

Inhibition of leukotriene synthesis markedly accelerates healing in a rat model of inflammatory bowel disease.

The role of leukotrienes in the pathogenesis of chronic colitis was investigated using a rat model. Ulceration and inflammation of the distal colon was initiated by the intracolonic administration of the hapten trinitrobenzene sulfonic acid in 50% ethanol. Leukotriene B4 synthesis increased significantly within 4 h after induction of damage, with the greatest increase observed 24-72 h after administration of the hapten. The increase in leukotriene B4 synthesis correlated well (r = 0.88) with an increase in colonic myeloperoxidase activity, a biochemical marker of neutrophil infiltration. Daily intracolonic treatment with a specific 5-lipoxygenase inhibitor, L651,392, during the first 4 days after initiation of colitis, resulted in significant reductions of colonic leukotriene B4 synthesis, colonic damage score, and colon wet weight. When examined 2 wk after initiation of colitis, the group treated with L651,392 (for the first 4 days) showed significantly less colonic damage (assessed macroscopically and histologically) and colonic inflammation (assessed histologically and by measurement of myeloperoxidase activity). The healing produced by treatment with L651,392 was comparable to that observed after treatment with 5-aminosalicylic acid in a similar manner. Although a reduction of colonic damage could be produced in this model by intracolonic pretreatment with a prostaglandin E1 analogue (rioprostil), the mechanism of action of L651,392 did not appear to be through prevention of the initial injury induced by the hapten and ethanol solution. These results demonstrate that inhibition of leukotriene synthesis results in a marked acceleration of the healing of colonic ulcers and resolution of colonic inflammation in this animal model of chronic colitis. The results are therefore consistent with the hypothesis that leukotrienes play an important role in the pathogenesis of intestinal inflammation.

The roles of ethanol and of acid in the production of gastric mucosal erosions in rats

SummaryThis study was undertaken to differentiate between the morphological changes produced in chambered rat gastric mucosae by 40% ethanol and by 50 mM HCl. 40% ethanol produced both focal mucosal hyperemia and widespread exfoliation of the surface epithelium. Massive release of mucus accompanied both events. In the absence of acid the released mucus was stabilized by a network of fibrin, and epithelial continuity was reestablished over non-hyperemic regions by migration of epithelial (and parietal) cells from the gastric pits. Hemorrhagic erosions occurred only in the presence of acid, but were limited to the hyperemic regions. Acid had the following effects: (1) platelet thrombi were destroyed, thus promoting hemorrhage; (2) destruction of the fibrin network by acid caused dissipation of the adherent mucous coat; (3) vulnerable cells which had previously shown only ischemic damage were irreversibly damaged by acid; (4) exposed basal lamina was destroyed, thus removing the substratum necessary for orderly epithelial re-establishment.

Villous damage induced by suction biopsy and by acute ethanol intake in normal human small intestine

Previous studies by us indicated that ethanol in concentrations of 2.0–4.8% produced subepithelial blebs in the jejunum of the hamster. In the rat, due to rupture of the blebs, there was denudation of the villus tip epithelium. There are no similar data on humans. Ethanol, in quantities equivalent to 4.8–6.4 ounces of 80 proof whiskey (diluted to 20% w/v), was infused into stomachs of 20 normal human volunteers. Subjects were divided into groups (Gr) according to the amount or type of alcohol given, and the site of biopsies (SB). Gr 1∶60 g ethanol, SB=jejunum. Gr 2∶45 g ethanol, SB=jejunum. Gr 3∶45 g ethanol, SB=duodenum. Gr 4∶45 g ethanol as 4.8 oz 80 proof whiskey, SB=duodenum. To compare the morphology in the absence and presence of ethanol, biopsies were obtained from each volunteer before ethanol administration (control period). immediately after peak ethanol concentration in the duodenum or jejunum (ethanol period), and when intraluminal ethanol concentration fell towards zero (recovery period). The mean peak intraluminal ethanol concentrations in the four groups varied between 5.69% and 9.37% (w/v). Ethanol-induced damage was evaluated using strict preset criteria. Coded slides were evaluated by two observers. Suction biopsy damaged 18% of the villi even in biopsies obtained during the control period. Ethanol produced a statistically significant increase in the number of damaged villi (mean of all groups 45%, range∶32% in Gr 2 to 62% in Gr 3). During the recovery period the number of damaged villi fell to that seen in control period biopsies. Ethanol, in quantities equivalent to those ingested during moderate drinking, may produce transient damage to the upper small intestine of man. Conversely, ethanol may simply increase the susceptibility of the mucosa to the unavoidable trauma of suction biopsy. However, the histological and ultrastructural changes were similar to those induced by ethanol in small laboratory animals.

The fine structure of the tegument and associated structures of the cercaria of Schistosoma mansoni.

SummaryThe tegument of the cercaria of Schistosoma mansoni resembles that of the adult in its basic organization but differs considerably in detail. The outer level of the cercarial tegument is thinner and contains several types of inclusion not found in the adult. Only rod-like bodies are characteristic of both stages. Although the cercarial spines are smaller than those of the adult they possess an identical substructure. The uniciliate sensory structures of the cercaria differ from those of the adult in that the cilium of the cercarial structure is not ensheathed in tegumental material. A second type of sensory structure bearing several cilia is located at the anterior tip of the cercaria. Three morphologically distinct types of penetration gland can be distinguished and the content of each is described.

A functional model for extracellular gastric mucus in the rat

SummaryThere is no morphologically detectable, continuous layer of extracellular mucus over the undamaged gastric mucosa of the rat. Instead, the mucosa is only partially covered by an interconnected network of mucous strands and sheets. This mucus is strongly acidic (sulphated) and is released by epithelial cells which line the isthmic and lower foveolar regions of the gastric glands of the fundus. A thick layer of gelatinous mucus is, however, released within 5 min after topical application of ulcerogenic agents. This mucus is released as a result of exfoliation and disintegration of interfoveolar surface epithelial cells. The released mucous glycoprotein is neutral or weakly acidic and is readily distinguished from the fibrous mucus produced by the epithelial cells which line the upper regions of the gastric glands. The preexisting network of acidic, fibrous mucus is retained at the luminal surface of the mucous cap which is produced over sites of damage. The layer of fibrous mucus is reinforced during the development of mucosal damage by accelerated release of mucous strands from the gastric glands. We propose that the fibrous mucus acts as an external, restraining layer to maintain the locally released, gelatinous mucus over sites of damage during a period in which epithelial continuity is restored by emigration of cells from the gastric glands.

Ultrastructure of neurosecretory cells in the pars intercerebralis of Rhodnius prolixus (Hemiptera).

Six neuron types are distinguished in the pars intercerebralis of the starved fifth instar of Rhodnius prolixus. All neuron types contain electron dense secretory granules derived from Golgi complexes which are of characteristic size and morphology in each type. The neuron types are not thought to represent stages in a secretory cycle. The variety of neuron types described is related to that revealed by staining sections of the same cells with paraldehyde fuchsin. Active synthesis of neurosecretory granules continues throughout starvation and the lysosomal system appears to be involved in the continual degradation of secretory granules. Some of the variations in granule morphology observed may be a consequence of granule fusion and the importance of cytoplasmic events in the development of neurosecretory granules is discussed.

Cell Loss from Normal and Stressed Gastric Mucosae of the Rat: An ultrastructural analysis

The gastric mucosa is characterized by high rates of surface epithelial cell (SEC) loss. Exposure to acute stressors results in an increase in the incidence of SEC loss. However, little is known about the detachment of SEC from the epithelial sheet. We have used scanning and transmission electron microscopy to study mechanisms of SEC loss from the gastric mucosae of normal, fasted rats and of rats exposed to acute stressors. In fasted control animals SEC loss occurred primarily via extrusion of individual interfoveolar cells and only rarely by degeneration in situ. Each extruding cell was surrounded by a rosette-like configuration of adjacent, encroaching SEC. Mucosal integrity is maintained. Short term exposure to acute stressors results in an increase in the incidence of extrusive cell loss. Continued exposure to stressors also increases the incidence of degeneration in situ of isolated SEC or groups of SEC. Extrusion provides a mechanism for the necessary removal of gastric SEC. Acute stress may override or exhaust the extrusive mode, producing, via ischemia or surface diffusion of cytotoxic agents, SEC degeneration in situ and breaks in the mucosal barrier.

Effects of acid on the basal lamina of the rat stomach and duodenum

SummaryRapid restitution of the gastric and intestinal epithelium after acute injury involves emigration of cells from the gastric glands and basal half of the intestinal villi. An intact basal lamina is prerequisite to the restitution process. The present study was performed to determine the effects of acid on the rat gastric and duodenal basal lamina. The basal lamina was denuded in vitro by ultrasonic vibration. The tissue was then immersed in 0.2 M mannitol (control) or in HC1 (5-50 mM) for 10 min. Samples of the tissues were examined by transmission and scanning electron microscopy. Some samples were stained with ruthenium red to demonstrate glycosaminoglycans. The lower concentrations of acid (5 and 10 mM) had little or no effect on the structure of the basal lamina. However, exposure to 20 and 50 mM HCl caused extensive damage to the basal lamina and exposed the underlying connective tissue matrix of the lamina propria. Ruthenium red staining demonstrated differences in size and location of glycosaminoglycans within the basal laminae of stomach and intestine. Exposure to acid at concentrations of 20 or 50 mM caused total loss of ruthenium red staining in both intestinal and gastric basal laminae. Exposure to 10 mM acid resulted in loss of the outermost (luminal) layer of anionic sites from the gastric basal lamina.These studies demonstrate that brief exposure to acid, in concentrations which are necessary for the formation of hemorrhagic erosions in the stomach, caused damage to the basal lamina. This damage may impair epithelial restitution and thus account, in part, for the role of acid in ulcerogenesis.

Morphological evidence of mast cell degranulation in an animal model of acid-induced esophageal mucosal injury.

In previous studies we have demonstrated that microvascular permeability increases early in the course of experimental acid-induced esophageal mucosal injury. This is associated with an increase in the intraluminal appearance of histamine, suggesting a possible role for mast cells in this form of injury. In the present study, quantitative analysis of esophageal mast cells was undertaken using both light and electron microscopy in opossums undergoing intraluminal esophageal acid perfusion or normal saline control perfusion. Light microscopy showed that animals perfused with either 50 or 100 mM hydrochloric acid had an approximate 50% decrease in the number of stainable esophageal mast cells. Stereologic analysis of electron micrographs revealed that within the mucosa, the mean area of the mast cells as well as nuclear area and area of intact granules were also significantly reduced in acid perfused animals. Taken together these quantitative morphological analyses suggest that intraluminal acid exposure is associated with degranulation and/or lysis of esophageal mast cells and that released mediators from esophageal mast cells may play a role in the pathophysiology of reflux esophagitis.

Correlations between changes in indicators of gastric mucosal barrier integrity at time of exposure to "barrier breakers" and extent of hemorrhagic erosions one hour later.

We have examined the effects of seven different “barrier breakers” (including ethanol, aspirin, salicylic acid, isobutyric acid, Na taurocholate, thermal injury, and hyperosmotic glucose) on chambered gastric mucosae of rats in an attempt to identify variations in accepted indicators of mucosal barrier integrity which would accurately predict the extent of subsequent hemorrhagic erosion. When results from all experimental groups were considered, only the initial decrease in transmucosal potential difference (PD) showed significant correlation with final damage (lesion area). When the results were analyzed as separate subgroups, significant correlations were also found between net K+ efflux during the first 10 min after luminal infusion and final lesion area. Only in the subgroup containing ethanol, salicylates, and thermal injury was there a correlation between net loss of luminal H+ (back-diffusion) and lesion area. These results are considered in terms of their implications for the ulcerogenic actions of each group of agents.