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Receptors for guanylin and uroguanylin were identified on the mucosal surface of enterocytes lining the intestine of the bobtail skink ( Tiliqua rugosa ), king's skink ( Egernia kingii ), and knight anole ( Anolis equestris ) by receptor autoradiography using 125 I-ST ( Escherichia coli heat-stable enterotoxin) as the radioligand. Specific, high-affinity binding of 125 I-ST to receptors was found on the microvillus border of enterocytes and little or no specific binding of 125 I-ST was observed in other strata comprising the gut wall. The American alligator ( Alligator mississippensis ) also exhibited receptor binding, but unlike the other three species had relatively high levels of apparent nonspecific binding. A comparison of intestinal cGMP accumulation responses between the American alligator and the knight anole demonstrated a greater magnitude of cGMP responses to ST and guanylin in vitro in the knight anole relative to the tissue cGMP accumulation responses of alligators. Treatment with ST resulted in markedly greater tissue cGMP accumulation responses in both species compared to treatment with guanylin. To complete a paracrine signaling pathway in reptilian intestine, guanylin-like peptides that stimulated cGMP accumulation in human T 84 intestinal cells were isolated from the intestinal mucosa of alligators. We conclude that functional receptor-guanylyl cyclases and one or more endogenous guanylin/uroguanylin-like peptides occur in the intestinal tract of reptiles as well as in the intestines of mammals and birds. Thus, higher vertebrates have a conserved signaling pathway that regulates intestinal function through the first-messenger peptides, guanylin and/or uroguanylin, and the intracellular second messenger, cGMP.

Guanylin and uroguanylin are newly discovered, related peptides that activate common guanylyl cyclase signaling molecules and via 3’,5’-guanosine cyclic monophosphate regulate the activity of a variety of tissues and organs. Additionally, the message for both peptides is expressed in a variety of tissues and organs, including the intestinal tract and kidney, and thus may serve as part of a functional endocrine axis linking these two major organ systems in fluid/volume homeostasis. This manuscript reviews the discovery and nature of the guanylin and uroguanylin peptides, their actions on the intestinal mucosa and kidney, the distribution and molecular biology of the guanylyl cyclase C receptor, and explores the future directions of this rapidly developing, expanding field of inquiry.

The intestinal hormone guanylin and bacterial heat-stable enterotoxins (STs) are members of a peptide family that activates intestinal membrane guanylate cyclase. Two different peptides that activate the human intestinal T84 cell guanylate cyclase have been purified from urine and intestinal mucosa of opossums (Didelphis virginiana). The highly acidic peptide, QEDCELCINVACTGC, was named uroguanylin because it was isolated from urine and shares 53% identity with guanylin. A second peptide, SHTCEICAFAACAGC, was purified from urine and intestinal mucosa. This alanine-rich peptide was 47% identical to uroguanylin and 73% identical to human guanylin, suggesting that it may be an opossum homologue of guanylin. Synthetic uroguanylin-(2-15) (i.e., EDCELCINVACTGC) was 10-fold more potent than synthetic rat guanylin, but both peptides were less potent than Escherichia coli ST in the T84 cell cGMP bioassay. Uroguanylin-(2-15) and guanylin inhibited 125I-ST binding to T84 cell receptors in competitive radioligand binding assays. Transepithelial Cl- secretion was stimulated by 1 microM uroguanylin, indicated by an increase in the short circuit current of T84 cells. Thus, uroguanylin is another paracrine hormone in the emerging peptide family that activates intestinal membrane guanylate cyclase. The second peptide may be the opossum form of guanylin, or perhaps, it is still another member of this peptide family. The presence of uroguanylin and guanylin in urine and receptors in proximal tubules suggests that these peptides may also originate from renal tissue and may regulate kidney function.

Light-microscopic and ultrastructural analysis of the ocular tissues of the North American opossum (Didelphis virginiana) revealed that the arterial and venous segments of retinal vessels, including capillaries of the smallest calibre, occur in pairs. They do not form anastomotic networks, the common pattern in mammals with vascularised retinae, but instead the two segments of the pair join to form hairpin end loops. The paired vessels, with the arteriolar limb usually on the vitread aspect, penetrate the retina and branch to form three distinct layers of capillaries. The most superficial lies in the nerve fiber layer, the middle is situated in the inner nuclear layer and the deepest extends to the external limiting membrane, which is considerably deeper than in normal mammalian holangiotic retinae. The paired capillaries display classical morphological features of central nervous system capillaries, i.e., they are lined by continuous endothelial cells united by tight junctions. The lining endothelium is supported by a distinct basal lamina that splits to envelop pericytes. The latter, although abundant, are invariably interposed between the two vessels that form each vascular unit. Phylogenetic and functional aspects of this unique form of retinal vascularisation are discussed.

Summary Relaxin-immunoreactivity was demonstrated in the cytoplasm in the luteal cells from pregnant and lactating opossums. Immunoreactivity for relaxin was not demonstrated elsewhere in the ovary, in the reproductive tract or in the placenta. The corpus luteum is thought to be the primary source of relaxin in Didelphis and in this regard is similar to several eutherian mammals including man.

The Harderian gland of the North American opossum (Didelphis virginiana) is large and well developed, despite the absence of a nictitating membrane in the adult of this species. The elongate glands are surrounded by a delicate connective tissue capsule from which thin septae extend, subdividing the gland into numerous lobules. The secretory units of the opossum Harderian gland are drained by a well defined but not extensive intralobular and interlobular duct system. Most of the secretory end pieces consist of tubulo-alveolar units with widely dilated lumina filled with secretory product. Numerous intact lipid vesicles suspended within an amorphous material constitute the luminal contents. Cells lining the tubulo-alveolar secretory end-pieces are usually columnar in shape, and characterized by numerous lipid-containing secretory vesicles and aggregations of poly-tubular complexes 40-60 nm in diameter. In addition, these cells contain numerous large irregularly shaped mitochondria, whose matrix is of considerable electron density. Intralobular and interlobular ducts are lined by electron-lucent epithelial cells that lack both the lipid-containing vesicles and the large mitochondria, although typical smaller mitochondria are found scattered within the cytoplasm. Both secretory end-pieces and ductal elements are invested by an abundance of myoepithelial cells. A second, smaller serous type of secretory unit may occur near the centre of some Harderian gland lobules. In these units secretory tubules and acini are compactly arranged surrounding a narrow lumen. Serous cells are pyramidal in shape and the cytoplasm is characterized by numerous electron-dense secretory granules and scattered profiles of rough endoplasmic reticulum.(ABSTRACT TRUNCATED AT 250 WORDS)

The endoderm of the 9-day opossum forms the innermost layer of the embryo and also lines the interior of the chorion (Krause and Cutts 1985b). At this stage, the embryo appears as a flattened disk and consists of ectoderm, mesoderm, and endoderm, Cell boundaries between individual endodermal cells are distinct, and microvilli on the apical surfaces of the cells are short and scattered (Fig. 26). No obvious differences are seen between the endodermal cells that line the interior of the yolk sac chorion and those that form the third layer of the opossum embryo (Krause and Cutts 1985b,c). The endoderm consists of a single layer of cuboidal cells which are joined by junctional complexes and often bear elongated processes that unite with similar processes of adjacent endodermal cells. The intercellular space formed between the processes usually appears empty. The cytoplasm of the endodermal cells is characterized by numerous free ribosomes, occasional profiles of granular endoplasmic reticulum, and scattered mitochondria. There is little morphological evidence to suggest absorptive activity by the endoderm at this time in Didelphis. Similar observations have been reported in the Philander opossum (Enders and Enders 1969).

Various factors influence the differentiation, growth, and function of the glands associated with the gastrointestinal mucosa and also play an important role in regulating and maintaining the balance between epithelial cell proliferation and loss of cells from the gastrointestinal mucosa. Although the nature of the activities of such substances in Didelphis is unknown, there appears to be no reason to believe that they function in any way different to those in other mammals. Differentiation and growth, as well as epithelial cell proliferation and loss, are influenced by luminal, dietary, neural, and hormonal factors. Preprogrammed intrinsic factors also may play an important role in the regulation of the processes. The effect of such factors on gastrointestinal differentiation and growth have been summarized in elegant reviews by Klein and McKenzie (1983a,b), and by Johnson (1987) and Henning (1987). These factors include hypophysial hormones or tissues under hypophysial control, endogenous gastrointestinal hormones from enteroendocrine cells, neurotransmitters from the enteric nervous system, factors present in luminal content (amniotic fluid, milk, or dietary factors), and intrinsic mechanisms such as prostaglandins and chalones. Gastrin-, CCK-, somatostatin-, BPP-, glucagon-, secretin, motilin-, GIP-, neurotensin-, and 5-HT-immunoreactive cells are present in the gastrointestinal mucosa of the newborn opossum (Krause et al. 1986, 1989b). Cells with neurotensin immunoreactivity are unique in that, although present in the proximal colon of the newborn, the cells disappear and a significant population is not seen again in the intestinal mucosa until the 74th postnatal day, just prior to weaning.

We studied the effect of either placebo, 16,16-dimethyl-prostaglandin E2 (16,16-dimethyl-PGE2), or cimetidine on spontaneous degeneration of isolated rat gastric glands maintained in vitro in a basic oxygenated medium for 24 h. We assessed the viability of gland cells with fast green exclusion, measured release of lactate dehydrogenase (LDH) into the medium, and assessed the cell ultrastructure using a scanning electron microscope. Gastric glands incubated in medium for 6, 12, and 24 h underwent spontaneous degeneration reflected by a decrease in cell viability, increase in LDH release into the medium, and ultrastructural cell damage. 16,16-Dimethyl-PGE2 either at 0.1, 1, or 10 micrograms/ml significantly reduced the decrease in cell viability, increasing cell survival; reduced LDH release into the medium; and ultrastructural damage. Incubation with cimetidine at 1 or 10 micrograms/ml did not affect cell viability at 6, 12, or 24 h, whereas 100 micrograms/ml reduced cell viability (vs. placebo) at 12 and 24 h. LDH release and ultrastructural damage were not affected (not reduced) by cimetidine. Our study indicates that 16,16-dimethyl-PGE2, but not cimetidine, directly protects isolated gastric gland cells against degeneration in vitro, under conditions independent of systemic, neural, and hormonal factors.

It has long been assumed that the mucosa in areas of grossly 'healed' gastric or duodenal ulcers returns to normal, either spontaneously or after treatment. This assumption is based almost entirely upon visual, superficial examination by endoscopy. Few, if any, histological and ultrastructural studies examined the deeper mucosa in the areas of grossly healed ulcers. In several experimental studies, we analysed the development, evolution, and healing of acetic acid-induced gastric ulcers in rats and assessed the histological and ultrastructural features (structure and cellular composition) of the gastric mucosa in areas of grossly healed ulcers. The gastric mucosa of grossly 'healed' ulcers showed re-epithelialization of the mucosal surface at every study interval (2 weeks, 2, 3, and 4 months), but the subepithelial mucosa displayed prominent abnormalities. Two patterns of scarring were distinguished: (a) the mucosa in the area of healed ulcer was thinner (25-45% thinner than normal mucosa) with increased connective tissue and poor differentiation and/or degenerative changes in the glandular cells; and (b) the mucosa displayed a marked dilation of gastric glands with poor differentiation of the glandular cells and a reduction in the supportive microvascular network. It is theorized that these abnormalities could interfere with oxygenation, nutrient supply, and mucosal resistance and defence; therefore, they could be a basis for ulcer recurrence. These observations indicate that the quality of mucosal structural restoration rather than the speed of ulcer healing is the most important factor in determining risk of ulcer recurrence. The clinical relevance of these findings is supported by a preliminary study in which marked histological abnormalities were found in the subepithelial mucosa in patients with 'healed' duodenal ulcers.

Assessment of gastric ulcer healing is usually based on a visual examination (by endoscopy in patients, or the evaluation of ulcer size in experimental studies), and not on histologic and ultrastructural assessment of subepithelial mucosal healing. This approach has led to the assumption that the mucosa of grossly "healed" gastric and/or duodenal ulcers returns to normal, either spontaneously or following treatment. However, the re-epithelialized mucosa of grossly "healed" experimental gastric ulcer has recently been found to have prominent histologic and ultrastructural abnormalities, including reduced height, marked dilation of gastric glands, poor differentiation and/or degenerative changes in glandular cells, increased connective tissue, and disorganized microvascular network. It has been postulated that these residual abnormalities might interfere with mucosal defense and may be the basis of ulcer recurrence. In the present article, the ulcer healing process and the role of luminal factors, transitional zone at the ulcer margin, and granulation tissue are discussed. The healing of an ulcer is accomplished by filling of the mucosal defect with epithelial cells and connective tissue to reconstruct mucosal architecture. Under influence of growth factors [predominantly epidermal growth factor (EGF) and transforming growth factor (TGF alpha)], the epithelial cells at the ulcer margin dedifferentiate and proliferate, supplying cells for re-epithelialization of the mucosal scar surface and reconstruction of glandular structures. Granulation tissue at the ulcer base supplies connective tissue cells to restore the lamina propria and endothelial cells and microvessels for mucosal microvasculature reconstruction. The final outcome of healing reflects a dynamic interaction between an "epithelial" component from the ulcer margin and a connective tissue component including microvessels originating from granulation tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

The occurrence and properties of PTH-related peptide (PTH-RP) in milk was investigated. PTH-RP was purified to homogeneity from human and bovine milk using heat and acid to precipitate milk proteins followed by ion exchange chromatography and reverse-phase HPLC. The peak of PTH-RP from HPLC was detected using a sensitive bone cell bioassay. A single band of peptide was detected on silver-stained polyacrylamide gels, which migrated as a 20-21-kDa macromolecule. PTH-RP isolated from either human or bovine milk had similar electrophoretic mobilities on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The partially purified bovine PTH-RP stimulated cAMP production in UMR106-01 and OK cell lines and elicited a concentration-dependent inhibition of sodium-dependent phosphate transport in OK cells. Incubation of milk extracts with an anti-PTH antiserum did not affect their bioactivity, whereas an antihuman PTH-RP 1-34 antiserum markedly reduced the cAMP response of UMR106-01 cells to the immunoabsorbed milk extracts. A PTH antagonist, norleu PTH 3-34, blocked the stimulation of cAMP production in UMR106-01 cells treated with milk extracts. PTH-RP immunoreactivity and bioactivity occurred in milk extracts of diverse animals from both eutherian and metatherian (marsupial) species. Porcine colostrum also had immunoreactive PTH-RP, although the levels were lower than the immunoreactive PTH-RP concentrations observed in milk samples collected at 7 and 14 days of lactation. Thus, a 20-21-KDa PTH-RP is secreted into milk where it could play a role in the development of suckling, newborn animals.

The present study examined the time sequence and histologic and ultrastructural features of the formation and evolution of experimental, acetic acid-induced gastric ulcerations in rats. One hundred percent acetic acid was applied to the gastric serosa of 140 fasted male Sprague-Dawley rats through a polyethylene tube for 30 s. Gastric mucosal changes were evaluated at 1, 5, 15, and 30 min, 1 and 3 h, and 1, 2, 3, 5, 8, and 11 days after acetic acid application by visual inspection, by quantitative and qualitative light microscopy, and by transmission electron microscopy. Following exposure to acetic acid, the earliest morphologic changes occurred at 1 min and consisted of dilatation of large submucosal veins and arteries and mucosal collecting venules. Five to 15 minutes after injury, thrombi developed in submucosal veins and collecting venules, leading to microvascular stasis and mucosal necrosis. By 3 h, necrotic masses started to detach. By 24-48 h, necrotic changes penetrated the submucosa. By 72 h, most ulcers underwent transition into a "chronic" stage characterized histologically by the presence of granulation tissue at the bottom, and the appearance of a transitional healing zone at the margins. By 5 days, an increased amount of granulation tissue was observed and the gastric glands in transitional zones at the ulcer margin displayed cystic dilatation. Based on this study, we conclude that a key feature of acetic acid-induced ulcer formation is the early vascular and microvascular injury, which precedes glandular cell necrosis.

Parathyroid III of the opossum, Didelphis virginiana , lies on the medial surface of the internal carotid artery at its origin just above the bifurcation of the common carotid artery. It is limited externally by a capsule and is subdivided into lobule-like structures by connective tissue septae. The parenchyma consists solely of chief (principal) cells,' arranged in irregular cords and clumps supported by a delicate vascular connective tissue. Ultrastructurally, the chief cells are polyhedral in shape and have centrally placed nuclei. The cytoplasm contains small, randomly distributed, rod-shaped mitochondria, scattered profiles of granular endoplasmic reticulum, free ribosomes, and small perinuclear Golgi complexes. Secretory granules are small, electron-dense, and appear to be limited by a delicate membrane. The granules are related both to the Golgi complex and the basal cell membrane. Capillaries that lie immediately adjacent to the chief cells show an extensively fenestrated endothelium.

The effect on parietal cells of glucagon given prior to pentagastrin is unknown. Fifteen healthy volunteers were studied during constant intravenous infusion of pentagastrin (2 micrograms/kg body weight/hr) and during pentagastrin infusion initiated 20 min after intravenous injection of 2 mg glucagon. Three types of studies were performed: Gastric mucosal biopsies were obtained with a Quinton instrument. Electron micrographs of 320 parietal cells were analyzed by the Loud quantitative method, and intragastric pH (pH probe), or gastric potential difference (PD) were recorded continuously. Pentagastrin infusion produced a significant increase in canalicular and simultaneous reduction of tubulovesicular membrane area of parietal cells. Glucagon pretreatment did not inhibit canalicular and tubulovesicular membrane reaction to pentagastrin; unexpectedly this reaction was significantly greater when compared to that after pentagastrin alone. Initiation of pentagastrin infusion in subjects pretreated with glucagon produced a greater absolute value drop in gastric PD (23 +/- 2 mV) and an earlier drop in intragastric pH (3 min) than in subjects receiving pentagastrin infusion alone (13 +/- 1 mV and 10 min, respectively). In conclusion, at the doses studied, glucagon pretreatment increases parietal cell canalicular reaction to pentagastrin.

We studied aspirin-induced injury to the gastric mucosa in control rats pretreated with a solubilizer, pluronic F-68 (PL), and in rats pretreated with solubilized arachidonic acid (AA). Fasted male rats were pretreated intragastrically with 1 ml of either pluronic or AA and 1 h later acidified ASA (1 ml suspension of 200 mg kg-1 body weight) was administered intragastrically. Grossly apparent mucosal lesions developed 1 h after aspirin in pluronic-pre-treated rats, but were significantly reduced in AA-pretreated rats. Histology, scanning and transmission electron microscopy demonstrated that AA pretreatment did not prevent aspirin-induced initial damage to the surface epithelium but did significantly reduce extent of aspirin-induced deep mucosal necrosis at 1,4 and 18 h after aspirin. Initial aspirin-induced surface epithelial damage was rapidly restituted by two distinct types of re-epithelialization - vertical and horizontal. While the vertical type of re-epithelialization has been reported previously as the first stage of mucosal repair following injury by various noxious agents such as concentrated ethanol, the horizontal type of re-epithelialization, which is described for the first time in this paper, seems to be specific for the repair of aspirin-induced gastric mucosal injury. These studies suggest that dietary factors such as essential fatty acids may play a role in gastric mucosal protection against aspirin injury.

Numerous transitory intercellular attachments are observed between the central, lateral surfaces of adjacent glomerular epithelial cells in the differentiating renal corpuscle. The junctions are characterized by an increased electron density of the adjacent cell membranes and cytoplasm. The intervening intercellular space may contain an amorphous material of moderate electron density. The distribution and position of such temporary cell attachments, together with their modification and subsequent loss during the differentiation of podocytes, suggest that they play an important role in the histogenesis of the glomerular epithelium.

Cells immunoreactive for insulin, glucagon, somatostatin, bovine pancreatic polypeptide and 5-hydroxytryptamine are found in the pancreas of the newborn opossum and of all later stages examined. All immunoreactive cell types are present in primary and secondary islets and within elements of the exocrine pancreas. Cells immunoreactive for glucagon, bovine pancreatic polypeptide, somatostatin and 5-hydroxytryptamine generally are confined to the periphery of secondary (intralobular) islets, whereas insulin-immunoreactive cells occupy the central region. Endocrine cells within primary (interlobular) islets are randomly scattered. A small number of pancreatic-polypeptide-immunoreactive cells are reactive for the amine 5-hydroxytryptamine also, but the reverse is not observed.The endocrine pancreas continues to differentiate and develop throughout postnatal life and into adulthood. Little difference was observed between the head and tail regions of the opossum pancreas for the measurements made.

Aspirin, acetyl salicylic acid, damages gastric mucosal cells. This effect is considered related to its inhibition of prostaglandin synthesis. On the other hand, sodium salicylate has been reported to be cytoprotective against drug damage to gastric mucosa in vivo. One reason for this difference is that salicylic acid, unlike acetyl salicylic acid does not inhibit prostaglandin synthesis by gastric mucosa in vivo. Previous studies on tissue culture cells from our laboratory have required gastric mucosa from fetal rats; this was time consuming and expensive. The purpose of this study was to develop a primary cell culture of adult rat fundic epithelial cells and to test the effect of sodium salicylate on: (1) prostaglandin (PGE2) production, (2) cell viability, (3) reducing cell damage by sodium taurocholate. Gastric epithelial cells were isolated from adult rat stomachs and cultured on collagen gel. Cells reached confluency on day 4 at which stage fibroblasts were rarely seen (less than 1%). Autoradiographic study showed that cultured cells incorporated [3-H] thymidine into nuclei. In histochemical studies, 94% of the cells contained PAS positive granules (mucous cells). Mucous granules were observed in the cytoplasm of the majority of cells by electronmicroscopy. These cells synthesised prostaglandin E2 as determined by radioimmunoassay. Indomethacin 10(-4) M strongly suppressed PGE2 production after 30 minutes while 10(-3) and 10(-4)M sodium salicylate had no effect. Pharmacologic concentrations of 10 mM sodium salicylate had no effect on PGE2 production at 30 minutes and only weakly inhibited production after one hour incubation. Sodium salicylate up to 30 mM had no effect on cell viability, a concentration of 50 mM being necessary to produce significant cell damage. Sodium salicylate 10 mM significantly protected cells against damage induced by 10 mM sodium taurocholate. We conclude: (i) adult rat gastric mucous epithelial cells can be successfully cultured in vitro; (ii) prostaglandin synthesis is inhibited by indomethacin but not by low doses of sodium salicylate; (iii) sodium salicylate does not damage gastric mucosal cells except at very high concentrations; (iv) sodium salicylate protects against damage to cells induced by sodium taurocholate.

Two aspirin tablets in 100 ml fluid will produce microscopical damage to the human stomach. A study was performed to determine whether a small amount of sodium bicarbonate (equivalent to one-third of a teaspoonful of baking soda) could protect against this damage. Sequential gastric biopsy specimens were taken from 15 healthy subjects before, during, and after intragastric instillation of one of the following isotonic solutions: saline; sodium bicarbonate; 600 mg aspirin suspended in sodium bicarbonate; and aspirin suspended in saline. On a separate day the same solutions were instilled, but gastric transmucosal potential differences were monitored. Light microscopy and scanning electron microscopy of the biopsy specimens showed occasional mucous degranulation of mucosal surface cells, but no cell damage during instillation of sodium bicarbonate. Light microscopy studies 10 minutes after aspirin in saline showed damage in 20% of surface cells, with focal areas of cellular disruption and microscopic erosions, but only 3.4% of cells were damaged after aspirin in bicarbonate and there were no erosions. Electron microscopy showed a damaged honeycombed appearance of surface epithelium after aspirin in saline and a normal cobblestone appearance after aspirin in bicarbonate. Aspirin dissolved in bicarbonate failed to induce the usual fall in potential difference.These findings indicate that sodium bicarbonate in amounts equivalent to one-third of a teaspoonful of baking soda protects the gastric mucosa against aspirin-induced damage and prevents the usual fall in potential difference after aspirin.

The human pyloric glands are simple or branched tubular glands which spiral through the connective tissue of the lamina propria. They are comprised of three cell types: the pyloric gland (mucous) cell, the parietal cell, and endocrine cells. The mucous cell is the most common cell type in the human pyloric glands and is characterized by an abundance of secretory granules. The secretory granules are usually round in shape and vary considerably in diameter. They are membrane-bound and comprise a heterogeneous population. The larger granules contain a light staining amorphous material and often possess an area of increased electron density near the limiting membrane of the granule giving them a mottled appearance. A smaller, more electron-dense secretory granule also is found both in relation to the Golgi complex and cell apex.The morphological observations indicate that the mechanism of mucin production by the mucous cells of the human pyloric glands may be similar to that reported in other mucin-secreting cells.

To determine the effects of aspirin and hydrochloric acid on human jejunal mucosa, three obese patients with a small intestinal bypass that opened on the abdominal wall as a mucous fistula were studied. An 80-mM solution of HCl, a 40-mM suspension of aspirin (equivalent to two tablets in a glass of water), and a combination suspension of 40 mM aspirin plus 40 mM HCl damaged a mean ± SE of 26 ± 130 (P

Development of the external musculature of the gastrointestinal tract has been studied in the stomach, small intestine and colon of the postnatal opossum. The muscle support is thin and poorly developed at birth, especially in the stomach and small intestine where only the inner layer is completely formed. The outer layer is discontinuous and formed by scattered myoblasts. The muscularis externa of the colon at birth is considerably thicker and both layers are present. Subsequent development of the muscularis externa consists of an early period of proliferative activity followed by hypertrophy. A low rate of mitotic activity continues throughout development and into the adult. Elements of the myenteric plexus are present at birth.

Prostaglandins have acid antisecretory and cytoprotective effects in gastric mucosa when given exogenously. This study's purpose was to isolate preparations of parietal and non-parietal cells from rat stomachs and to compare prostaglandin output by these cells. Gastric epithelial cells were isolated from rat stomachs using pronase. Cells from different incubation times were collected separately and enriched by discontinuous Percoll gradient. Cell types were identified by hematoxylin and eosin stain, succinic dehydrogenase activity (parietal cells), periodic acid Schiff staining (mucous cells), Bowie staining (chief cells) and electron microscopy. Prostaglandin E2 activity was measured by radio-immunoassay. Parietal cells were purified to over 90% while the non-parietal preparation contained 67% chief cells and over 31% mucous cells. By electron-microscopy, cell integrity was seen to be maintained. The parietal cell enriched fraction contained two and one-half times the amount of prostaglandin E2 that the non-parietal chief cell enriched fraction did, p less than 0.01. These results raise the question as to whether output of PGE2 by parietal cells could play a role in modulating gastric acid secretion directly by parietal cells as well as in protecting the deeper layers of gastric mucosa against damaging agents in-vivo.

The gastric mucosa of both the echidna and platypus is aglandular and the lining epithelium is stratified squamous. The latter exhibits three principle layers: stratum germinativum, stratum spinosum, and stratum corneum. The cytoplasm of cells composing the first two strata of both species shows bundles of tonofibrils and numerous free ribosomes. Cells of the stratum spinosum in the platypus also show numerous dense granules limited to the peripheral cytoplasm. The stratum spinosum of both species is comprised of fusiform-shaped cells whose adjacent cell membranes show extensive interlocking. The stratum spinosum of the echidna in addition shows numerous intercellular bridges. Cells of the stratum corneum become flattened and elongate and in the echidna nuclei near the surface appear to degenerate. Cells comprising the stratum corneum of the platypus exhibit well preserved nuclei and contain scattered large granules of varying electron density. Prior to sloughing, cells near the surface of both species show a separation of adjacent cell membranes. True keratinization is not found in the gastric lining epithelium of either species and the epithelium lining of the stomach of the echidna more closely represents a form of parakeratosis. Delicate papillae containing capillaries extend considerable distances into the overlying epithelium of both species and are thought to contribute to its nutrition.

A 3-year study of general growth and development revealed a uniform increase in body length of young pouch opossums during the first 10 weeks of life. Throughout this period, growth was linear and constant for all animals regardless of sex, litter size, or whether animals were obtained from first, second or third litters. Body weights were somewhat more variable, but there were no significant sex differences. Various aspects of external gross morphology are presented and discussed as they relate to growth of the young opossum.

Biopsies from the fundic mucosa of healthy volunteers were examined by scanning electron microscopy following blunt dissection and freeze fracture. The mucosal surface exhibited a cobblestone appearance. With increased magnification, microvilli could be demonstrated on the luminal surface of individual surface cells. Blunt dissection of the gastric mucosa revealed tubular gastric pits descending from the surface until they opened into branched tubular gastric glands. The gastric glands are irregular in outline due to the knoblike projections of individual parietal cells. The internal structure of the component cells also was examined with the scanning electron microscope following freeze fracture. Mucous granules were observed in the apical portion of surface epithelial cells. Lumina of parietal cell canaliculi were found to be continuous with the lumen of the gastric glands. Pepsinogen granules could be seen throughout the cytoplasm of chief cells. The blunt dissection-freeze fracture technique utilizing the scanning electron microscope allows, for the first time, a three-dimensional view of human gastric mucosa, including the gastric pits and glands as well as some of the internal architecture of component cells.

Receptors for the heat-stable enterotoxin produced by Escherichia coli were found in the kidney and intestine of the North American opossum and in cultured renal cell lines. The enterotoxin markedly increased guanosine 3',5'-cyclic monophosphate (cGMP) production in slices of kidney cortex and medulla, in suspensions of intestinal mucosa, and in the opossum kidney (OK) and rat kangaroo kidney (PtK-2) cell lines. In contrast, atrial natriuretic factor elicited much smaller increases in cGMP levels of kidney, intestine, or cultured kidney cell lines. The enterotoxin receptors in OK cells had a molecular mass of approximately 120 kDa when measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of receptors crosslinked with 125I-enterotoxin. The occurrence of receptors for the E. coli peptide in OK implies that these receptors may be involved in the regulation of renal tubular function in the opossum. E. coli enterotoxin caused a much larger increase in urine cGMP excretion (10- to 50-fold over control) than did atrial natriuretic factor when these peptides were injected intravenously into opossums. However, atrial natriuretic factor elicited a marked diuresis, natriuresis, and increased urinary excretion of calcium, phosphate, potassium, and magnesium. In contrast, the enterotoxin did not acutely influence OK fluid and electrolyte excretion. Thus the substantial increase in cGMP synthesis produced by the bacterial peptide in OK cortex and medulla in vitro and the increased renal excretion of cGMP in vivo were not associated with changes in electrolyte or water excretion. Whether cGMP represents a second messenger molecule in the kidney is an interesting question that was raised but not answered in this series of experiments.

Spermatozoa of the opossum, Didelphis virginiana, were taken from three different regions of the epididymis and examined by scanning electron microscopy, phase-contrast and dark-field microscopy. It has been demonstrated that marked morphological changes occur in spermatozoa during their passage through the epididymis. In the first segment or head of the epididymis, spermatozoa are non-motile and the long axis of their nuclei is perpendicular to that of the tail. The nucleus is V-shaped with a thick and a thin arm. At the junction of the two arms. At the junction of the two arms, where the arms join, the articular fossa receives the capitulum of the connecting piece which attaches the head of the spermatozoon to the tail. Spermatozoa from the central region of the epididymis show a re-orientation of the nuclei which now lie parallel to the long axis of the tail. Both paired and unpaired spermatozoa are found and show an increase in motility. In the caudal region of the epididymis all spermatozoa are paired. Pairing occurs as a result of the close apposition of adjacent cell membranes covering the acrosomes of the larger arms.

Histologic or ultrastructural evidence of the ability of sucralfate to protect the gastric mucosa against ethanol injury is lacking. Therefore we analyzed morphologic and functional changes in the mucosa of 120 rats receiving, intragastrically, 2 ml of either sucralfate 500 mg/kg body wt or a control solution and 1 h later 2 ml of 100% ethanol. At 15 min, 1, 4, 6, and 24 h after ethanol instillation, mucosal changes were assessed by macroscopic examination, quantitative histology, scanning electron microscopy, recordings of gastric potential difference, and measurements of volume, pH, and electrolytes in the gastric contents. Between 15 min and 24 h after ethanol instillation, macroscopic necrotic lesions in controls involved greater than 33% of mucosal area and in the sucralfate-treated group less than 4% (p less than 0.001 for each period). In controls, ethanol instillation produced surface epithelial cell disruption and deep (greater than 0.2 mm) mucosal necrosis involving greater than 55% +/- 3% of the mucosal length. In sucralfate-pretreated animals, disruption of the surface epithelium was present at 15 min, 1 h, and 4 h after ethanol instillation, but deep necrotic lesions were virtually absent (0%-2%; p less than 0.001 vs. controls) during the entire study period. The surface epithelium was mostly reestablished by 6 h after ethanol instillation in the sucralfate group but not in the controls. We concluded that sucralfate protects the gastric mucosa against ethanol-induced injury by preventing deep mucosal necrosis and as a consequence the mucosal proliferative zone cells rapidly restitute mucosal integrity.

The duodenal glands of the species examined (Alces alces, Ovis canadensis, Cervus canadensis, Oreamnos americanus, Bison bison, Antilocapra americana, Odocoileus virginianas, Odocoileus heminous) are confined primarily to the submucosa of the small intestine. In one species, the moose, a significant population of secretory tubules also is observed in the mucosa. The ducts of the duodenal glands pierce the overlying muscularis mucosae to empty most often independently into the intestinal lumen. Those of the bison, unlike the other species examined, drain into intestinal glands. The duodenal glands consist primarily of a simple columnar epithelium, the cells of which contain basally positioned round or oval nuclei. The lumina of scattered duodenal glands in the pronghorn and to some extent those of the moose, white-tailed deer, and mule deer may be extremely dilated, and the surrounding epithelium thin and attenuated. Component cells of the duodenal glands of all the species examined show remarkably similar ultrastructural features. They exhibit scattered profiles of rough endoplasmic reticulum, dilated cisternae of which contain an electron-dense, amorphous material. Numerous well-developed Golgi complexes occupy the supranuclear region together with transport vesicles and forming secretory granules. Electron-dense, membrane-bound secretory granules generally are concentrated in the apical cytoplasm immediately subjacent to the cell membrane. The apical cell membrane exhibits short, scattered microvilli; and the basal cell membrane is smooth without apparent specialization. Histochemically, the duodenal glands of most species examined in this study consist of a heterogeneous population. The majority of the glands of the moose, elk, mountain goat, bison, pronghorn, and white-tailed deer elaborate a neutral mucin, whereas scattered individual glands, tubules or cells also produce acid mucins. Cells near the terminations of the ducts of the bighorn sheep are the only elements to produce acid mucins in the duodenal glands of this species. The duodenal glands of the bison are unusual in that only the peripheral portions of individual glands produce acid mucins. The remainder of the glands elaborate neutral mucins. Morphological differences between the two regions were not observed. The duodenal glands of the mule deer secrete both acid and neutral mucins. The structural and histochemical observations appear unrelated to the diet of individual species.

Although the action of sucralfate on ulcerated mucosa has been demonstrated, its effect on the histology, ultrastructure, and function of normal gastric mucosa is unknown. We investigated the effect of acute administration of sucralfate on the gastric mucosal history, ultrastructure, mucosal potential difference, and luminal release of prostaglandin E2. At 15 min, 1 h, and 3 h after intragastric instillation of sucralfate, whitish incrustations of the drug were firmly adhering to the glandular mucosa. Mucosal histology after sucralfate administration demonstrated the following: disruption and exfoliation of some of the surface epithelial cells, mucosal hyperemia, prominent release of mucus from the surface epithelial cells, and edema of lamina propria and submucosa. These changes were most prominent in the areas where sucralfate was in contact with the mucosal surface. Scanning and transmission electron microscopy confirmed the above changes. Sucralfate produced a drop in gastric mucosal potential difference and a significant increase in luminal release of prostaglandin E2. Sucralfate produces distinct morphologic and functional changes in the normal gastric mucosa, which may account for its preventive and therapeutic efficacy.