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The majority of human cardiac glands that lie immediately distal to the termination of esophageal epithelium are compound or branched tubular glands. They empty into overlying gastric pits. The glands of this region are often organized into lobule-like complexes by the surrounding connective tissue of the lamina propria. The secretory tubules contain mucous cells, parietal cells and endocrine cells. The mucous cell is the most common cell type observed and appears to comprise two populations. The majority are pyramidal in shape and show numerous spherical, electron-dense secretory granules. Profiles of rough endoplasmic reticulum are observed scattered throughout the cytoplasm and Golgi complexes occupy a supranuclear position in relation to forming secretory granules. Morphologically this cell type appears similar to the mucous neck cell of the fundus. Secretory granules of a second mucous cell type are mottled in appearance and show an area of increased electron density near the limiting membrane. Parietal cells are observed and appear identical to those in the fundus. The large number of endocrine cells present raises questions concerning the traditional concept of the function of these particular glands.

The purpose of this study was to develop a primary cell culture system of rat gastric fundic epithelial cells. The cells, isolated enzymatically, were cultured in Coon's modified Ham's F-12 medium supplemented with 10% fetal bovine serum, 15 mM HEPES buffer, fibronectin, and antibiotics. The inoculated cells started to grow rapidly on day 1 (doubling time, 26 h). The cells reached confluency on day 3. On phase contrast microscopy, over 90% of cells possessed epithelial characteristics. Histochemical studies showed (a) 90% of the epithelial cells contained PAS positive granules, (b) 5% of the cells gave a strong reaction for succinic dehydrogenase activity (presumably parietal cells), and (c) immunohistochemical localization of pepsinogen was negative. Ultrastructurally, microvilluslike structures, junctional complexes, Golgi apparatus, mitochondria, rough-surfaced endoplasmic reticulum, and mucous granules were observed. Mitotic figures were clearly observed on Giemsa staining and the mitotic index was maximum on day 2. Autoradiographic and biochemical studies showed these cells possessed the capability to synthesize deoxvribonucleic acid and this ability was maximum on day 2. These cells were able to synthesize and to secrete glycoprotein and this function was significantly increased by 16,16-dimethyl prostaglandin E2. Cyclic adenosine monophosphate produced by the cultured cells was enhanced by addition of 16,16-dimethyl prostaglandin E2 (p

Endocrine cells of gastric and gut mucosa are commonly thought to be present only within mucosal glands. In a previous report, we described argyrophilic cells in the lamina propria in 40% of surgical gastric specimens, using light microscopy. All these patients had chronic gastritis. Argyrophilia, however, is a non-specific reaction which could occur in other than endocrine cells. The present study was undertaken to describe the ultrastructure of argyrophil cells in the lamina propria. In five patients with chronic gastritis, endoscopic biopsies were taken from the fundic, intermediate, and pyloric areas of the stomach. Single and/or clustered argyophil cells were seen by light microscopy in the lamina propria of the intermediate and pyloric areas. On electron-microscopy, these cells had the following characteristics of endocrine-like cells: they were characterised by numerous electron dense granules in the cytoplasm, 100-300 nm in diameter; the cytoplasm contained poorly-developed rough endoplasmic reticulum and well-developed smooth endoplasmic reticulum with occasional vesicles. Immunostaining gave negative results for various gastrointestinal hormones. These ultrastructural characteristics of lamina propria cells are similar to endocrine cells of the APUD series. We conclude that endocrine-like cells occur in the lamina propria of the human stomach in the presence of chronic gastritis.

Effects of vitamin D deficiency (-D) on mineral homeostasis were investigated in Japanese quail embryos. The -D embryos from 1,25(OH)2D3-fed hens became progressively calcium deficient, as documented by hypocalcemia and reduced calcium accumulation by the skeleton, yolk sac, and allantoic fluid. Plasma phosphate was progressively elevated between days 11 and 15. Increased calcium accumulation by the skeleton, yolk sac, and allantoic fluid occurred between days 12 and 15 in +D embryos. Phosphate and adenosine 3',5'-cyclic monophosphate (cAMP) concentrations of allantoic fluid increased in +D embryos during the period of shell calcium mobilization. Further increases in phosphate and cAMP excretion into allantoic fluid occurred in -D embryos, although no calcium was absorbed from the shell. Renal 25(OH)D-1-hydroxylase activity increased between days 11 and 13, whereas the adenylate cyclase response to parathyroid hormone was lost in -D embryos by day 14. These changes in renal function are indicative of secondary hyperparathyroidism in the -D embryos. Differentiation of villus cavity and capillary covering cells occurred in the chorionic epithelium of -D embryos, but eggshell calcium was apparently not absorbed. In contrast, 75% of the total body calcium of newly hatched (+D) chicks was obtained from the eggshell. Thus the dissolution and/or transport of eggshell calcium is dependent on vitamin D in quail embryos.

The effect of glucagon on aspirin-induced damage to human gastric mucosa and its effect on gastric mucosal potential difference were studied in 29 healthy volunteers. Intragastric instillation of 600 mg of aspirin suspended in 100 ml of isotonic saline caused significant damage to 21 ± 3% of surface epithelial cells and a marked reduction in gastric potential difference within 15 min of aspirin instillation. Glucagon, 2 mg given intravenously, caused hyperglucagonemia, hypophosphatemia, hyperinsulinemia, increased blood glucose levels and gastric p H, as well as significant prolonged elevation of gastric potential difference. Glucagon injection given 15 min before aspirin instillation effectively prevented surface epithelial cell damage, decreasing percentage of damaged cells to 3.5%. Glucagon did not prevent the drop in gastric potential difference evoked by aspirin, but did, however, prevent potential difference from falling below base line values after aspirin. This study showed in man that glucagon protects gastric mucosa against aspirin damage and suggests possible therapeutic value in clinical situations requiring prevention of aspirin-induced gastric mucosal damage.

Isolated human gastric glands from surgical specimens were preincubated in an oxygenated medium with placebo or 16,16 dimethyl prostaglandin E2 (dmPGE2) and incubated at 37 degrees C in either medium alone, medium containing 4.43 mM indomethacin or medium containing 8% ethanol. We assessed the viability of gland cells with fast green exclusion, release of lactate dehydrogenase (LDH) into the medium, and ultrastructural damage by scanning and transmission electron microscopy. Both indomethacin and ethanol significantly reduced the viability of placebo-pretreated glands, increased LDH release into the medium, and produced prominent ultrastructural damage. DmPGE2 significantly reduced both indomethacin and ethanol-induced injury, increased the number of viable cells, reduced LDH release, and diminished the extent of ultrastructural damage. These studies indicate that PG protection of gastric mucosal cells has a direct cellular action that is not limited to replacement of depleted endogenous PGs. PG protection in our experiments did not depend on PG's previously described systemic actions, such as protection of the microvessels, preservation of the mucosal blood flow, or stimulation of bicarbonate and mucus secretion.

Glucagon inhibits gastric acid secretion and increases the negativity of gastric mucosal potential difference (PD) in man. To test the hypothesis that the increased negativity of PD after glucagon in man could be due to decreased parietal cell canalicular membrane area, a quantitative ultrastructural analysis was carried out. Four healthy volunteers with normal gastric mucosa were submitted to biopsy before and 20 minutes after intravenous injection of 2 mg glucagon (G). This time corresponded with the maximal change in PD and a decrease in gastric acid secretion. Canalicular and tubulovesicular membrane area of 80 parietal cells (40 cells before glucagon and 40 cells after glucagon) were quantified by the Loud morphometric method. After glucagon, the oxyntic cell canalicular membrane area was reduced by one-fourth (P less than 0.05), while tubulovesicular membrane area showed an increase (P less than 0.05) at the same time. The decrease in the area of parietal cell canalicular membrane caused by glucagon may in part be responsible for increased negativity of the gastric PD caused by this hormone.

The intestinal mucosa of the platypus takes the form of numerous transverse surface folds. These folds are made up of a lamina propria covered by pseudostratified epithelium which lies on a thick modified basement membrane. The cells of the intestinal epithelium consist of columnar cells which generally resemble typical intestinal epithelium and cuboidal cells, which are undifferentiated in appearance, show few organelles and possess an electron lucent cytoplasm. Numerous desmosomes are found between the adjacent cell membranes of both cell types. Villi are absent and appear to be represented by the large surface folds. Intestinal glands are composed of columnar epithelium similar to that found in the intestinal glands of other mammalian species. Groups of these glands drain into common tubular ducts which follow a tortuous course and empty into the intestinal lumen between the surface folds. The peculiar morphological features of the platypus intestinal mucosa raise questions concerning traditional concepts of intestinal gland formation as well as the origin and migration of intestinal epithelium with regard to this particular species.

The aim of the present study was first to resolve controversies regarding the extent of prostaglandin protection ("cytoprotection") of the gastric mucosa against injury produced by 100% ethanol and second to determine time sequence and histologic, ultrastructural, and functional features of this protection. Fasted rats received intragastrically (A) 0.9% NaCl alone as a control, (B) 5 µg/kg of 16,16-dimethyl prostaglandin E 2 dissolved in 0.9% NaCl, and (C) 100 µg/kg of 16,16-dimethyl prostaglandin E 2 dissolved in 0.9% NaCl. Thirty minutes later, 2 ml of 100% ethanol was instilled. The gastric mucosa was assessed macroscopically, by quantitative histology, and by scanning and transmission electron microscopy for [ 3 H]thymidine uptake, mitotic activity, ion fluxes, and gastric potential difference determined at several time intervals (between 10 min and 16 h) after ethanol administration. Between 10 min and 16 h after ethanol administration macroscopic necrosis involved 27% ± 3% to 41% ± 4% of the mucosal area in controls (group A), but necrosis was prevented in groups receiving 16,16-dimethyl prostaglandin E 2 (groups B and C). In the control group, histology and electron microscopy showed extensive disruption of the surface epithelium and deep necrosis (>0.2 mm) involving >46% ± 4% of the mucosa between 15 min and 16 h after ethanol administration. Deep necrotic lesions were completely prevented by either dose of 16,16-dimethyl prostaglandin E 2 (groups B and C). The mucosal proliferative zone was severely damaged in controls (68% ± 5%) within the first hour after ethanol administration, whereas 16,16-dimethyl prostaglandin E 2 protected the zone from damage ( 2 prevented the occurrence of initial (at 15–30 min) morphologic and functional disruption of the surface epithelium after ethanol administration. However, initial disruption of the surface epithelium by 16,16-dimethyl prostaglandin E 2 (groups B and C) was followed by migration of cells from the mucosal proliferative zone; the result was prompt restoration of the surface epithelium and resumption of its barrier and transport functions.

The notochord was examined by light, transmission and scanning electron microscopy, in 25 pouch young opossums (Didelphis virginiana) ranging in age from 6 hr to 25 days post natum. In the newborn opossum, the notochord forms a thin cylinder within developing vertebral centra and presents diamond-shaped expansions in regions of the developing intervertebral discs. The opossum notochord differs from that of other species in that it appears to consist of a heterogeneous population of light and dark cells, and also in the thinness of the notochordal sheath which never attains the degree of development seen in other animals. The sheath is made up of thin cytoplasmic processes which arise both from the light and dark cells. The processes cross a mucopolysaccharide-filled space and then expand to form a thin cytoplasmic sheath that forms the external boundary of the space. The matrix of the cartilage immediately adjacent to the cytoplasmic sheath shows an increased concentration of microfilaments as compared to the cartilage further from the notochord. During postnatal development the notochordal tissue in the centra of the vertebral bodies decreases, while in the regions of the developing discs, there is a corresponding increase. At the end of the first week, notochordal tissue in the vertebral centra is represented only by a thin cylinder of mucopolysaccharide which contains cell fragments. In subsequent weeks, as ossification of the centra occurs, both the cartilage and notochordal tissue are replaced by bone. Notochordal tissue in the intervertebral regions contributes to the formation of the nucleus pulposus of the intervertebral discs. Despite its short gestation period of only 12 1/2 days, the basic structure and fate of the notochord in the opossum is similar to that of other mammals.

The postnatal development of the respiratory system in the opossum has been traced, using 102 specimens divided into 11 groups according to snout-rump length. At birth, the lung is markedly underdeveloped and is represented by a pumitive system of branching airways that end in a number of terminal chambers or sacs. The airways, constituting the conducting portion of the lung, are lined by columnar epithelium that is devoid of cilia and goblet cells. The terminal air chambers contain an extensive capillary bed and are surfaced by squamous epithelium interspersed with scattered cuboidal cells. By the 3 cm stage, bands of smooth muscle have differentiated in relation to the bronchial epithelium and scattered cilia are present in the epithelium of the trachea and bronchi. Air chambers immediately adjecent to established bronchi differentiate further and become incorporated into the bronchial tree and new air chambers develop at the most distal extent of the bronchial system up to the 15.5 cm stage. Numerous spaces lined by squamous epithelium, which represent the first appearance of the arbor alveolaris, appear within the cellular stroma of the lung of the 7 cm opossum. By the 20 cm (juvenile) stage, mature alveoli, containing many vacuolated cells, are present and a thick collagenous lamina has developed between the pleura and the lung parenchyma.

A large gland patch is found in the submucosa of the lesser curvature of the koala stomach near the entrance of the esophagus. It measures approximately 3 cm in diameter and is comprised of numerous invaginations continuous with the surrounding mucosa. The glandular invaginations drain into the lumen of the stomach by 25 to 30 large orifices. The mucosa of the gland patch invaginations differs from the mucosal lining of the stomach chiefly in thickness. The elongate gastric glands that comprise the invaginations exhibit an increased number of parietal and chief cells. Ultrastructural examination of the gland patch illustrates that the parietal, chief, and mucous neck cells are similar in structure to those of other mammalian species.

Brunner's glands in the platypus form a lobulated, glandular collar confined to the submucosa of the most distal portion of the stomach. The glands end immediately proximal to the gastrointestinal junction and excretory ducts empty in the region where the stratified squamous epithelium lining the stomach changes abruptly to the intestinal lining epithelium of the duodenum. An individual gland of Brunner is composed of several elongate lobules drained by intralobular ducts which often join to form a single excretory duct. Light and electron microscopic studies have shown the secretory tubules to be comprised of large, pyramidal cells limited basally by a delicate basal lamina. The ergastoplasm, cisternae of which are dilated and contain amorphous material, is associated with numerous ribosomes. In basal and perinuclear regions intercisternal granules and smooth surfaced vesicles are found. Numerous small vesicles found in supranuclear areas apparently form from the smooth membrane portions of ergastoplasm located adjacent to Golgi complexes. Membrane-bound amorphous granules of varying electron density occupy the apical cytoplasm and show a tendency to coalesce before emptying their contents into the adjacent lumen. The intralobular duct system is lined initially by a columnar epithelium which changes to a simple squamous form before the ducts combine to form a short excretory duct lined by stratified squamous epithelium. The epithelium lining the duct system contains relatively few organelles but appears to be engaged in a limited amount of synthesis and release of secretory material. Histochemical studies indicate that both the secretory tubules and the duct system elaborate a neutral mucopolysaccharide.

The duodenal glands of the adult opossum form a lobed, glandular collar in the submucosa immediately distal to the pyloric sphincter. They empty into funnel-shaped mucosal depressions. The depressions, which form two or three irregular rows that run parallel to the pyloroduodenal junction, are lined by either pyloric or intestinal epithelium. An individual gland of Brunner has an extensive intralobular duct system which terminates in a single excretory duct just prior to entry into a depression. Histochemical studies indicate that the duodenal glands elaborate a neutral glycoprotein whereas the duct system appears to produce both neutral and acidic elements. Light and electron microscopic studies have shown the duodenal glands to consist of large, pyramidal cells which lie on a distinct basal lamina. Discrete, mottled or pale secretory granules are found in close association both with the apices of the cells and with the Golgi complexes. The ergastoplasm, cisternae of which are dilated and contain amorphous material, is associated with polysomes and, in the supranuclear region, often becomes markedly dilated, forming what appear to be large vacuoles containing fibrillar material. Blebbing of the ergastoplasm results in the formation of several small vesicles, many of which lie in close association with the Golgi network. Direct membrane continuity has been noted between the two elements.

We appreciate the opportunity to respond to the insightful comments of Dr. Gerber (1) on our manuscript (2). We agree with Dr. Gerber's review on the significance of prostaglandins in the maintenance of gastric mucosal integrity and inhibition of gastric acid secretion

Each developing opossum embryo is surrounded by a shell membrane which completely separates embryonic and maternal tissues. During the eighth and ninth prenatal days, the embryos together with their limiting shell membranes float freely within the uterine lumen, surrounded only by the secretions of the uterus. The shell membrane is transparent, nonelastic, tough, and capable of extreme deformation. It consists of a mat of interwoven fibers which vary in external diameter, are electron dense, and show no apparent substructure. The morphology and arrangement of component fibers are similar throughout the width of the shell membrane.

Just prior to the emergence of the tooth into the oral cavity, a small circular crater forms in the gingival epithelium immediately above the crown. The craters appear to expand in diameter during eruption to accommodate the emerging crown of the tooth. The observations support the concept that the crown of the tooth does not actively push through and rupture the gingival epithelium, but rather that the epithelium degenerates and then the tip of the crown emerges into the formed defect.

The anatomy and histology of the adrenal gland in the adult opossum were found to be typical for mammals. The development of the adrenal medulla was also found to follow the typical mammalian pattern. Primitive sympathetic cells were found in both intra- and extra-adrenal locations in the newborn at a time when chromaffin precursor cells were migrating to the adrenal anlage. Pheochromoblasts first appeared within the forming medulla where at a later stage chromaffin cells could be observed forming columns of cells between adjacent sinusoids. Unlike in other mammals, much of this development takes place postnatally when the neonate is in the mother's marsupium. The value of the developing opossum adrenal medulla as an experimental model is stressed, since a significant amount of development takes place in an environment that is accessible to experimental manipulation.

The relative frequencies of endocrine cells and peptidergic nerve elements in the proximal small intestine of the adult platypus were studied by immunohistochemistry. Six kinds of endocrine cells - serotonin (5-HT)-, somatostatin-, gastrin-, motilin-, cholecystokinin (CCK)- and bovine pancreatic polypeptide (BPP)-immunoreactive cells - were identified in this study. These endocrine cells were found most frequently in the intestinal glands, in moderate numbers in the tubular ducts and were infrequent in the surface folds. 5-HT-immunoreactive cells were most numerous, somatostatin-, gastrin-, motilin- and BPP-immunoreactive cells were moderately numerous, whereas CCK-immunoreactive cells were rare. Five kinds of neuropeptides: substance P, vasoactive intestinal polypeptide (VIP), gastrin releasing peptide (GRP), somatostatin and leu-enkephalin, were detected in the intramural nerve elements. Substance P-, VIP- and GRP-immunoreactive nerve fibers were found most frequently in the lamina propria mucosae of the surface folds. The relationships between the possible functions of the peptides and amine detected in this study as well as the characteristic structure of the digestive tract of the adult platypus are discussed.

Three clonal subpopulations of opossum kidney (OK) cells were derived from the parental line. The distribution of apical microvilli suggested that the OK cell line was heterogeneous. The clonal OK sublines appeared homogeneous as reflected by microvilli, which were uniformly distributed on the apical surface. Parathyroid hormone (PTH), forskolin (FSK), and prostaglandin E1 (PGE1) increased adenosine 3',5'-cyclic monophosphate (cAMP) formation in OK cells and all of the clones. PTH inhibited sodium-dependent phosphate transport in parental cells and in OK/B and OK/P clones with maximal effects appearing at 4, 2, and 1 h, respectively. PTH had no effect on phosphate transport in OK/H cells. FSK inhibited phosphate transport in parental cells and OK/B and OK/P clones but was relatively ineffective in OK/H cells. PGE1 decreased phosphate transport in OK/B and OK/P cells but was ineffective in the parental line and in OK/H cells. Phorbol 12-myristate 13-acetate, a potent inhibitor of phosphate transport in the parental OK cell line, had little effect in the clonal sublines. These clonal lines have remained phenotypically stable for 10 passages and should prove useful in studying the regulation of phosphate transport by PTH as well as addressing the question of whether PTH receptor subclasses exist which couple to cAMP and/or calcium effector systems in kidney cells.

The distribution of receptors for Escherichia coli enterotoxin were examined in opossum kidney, intestine, and testis. E. coli enterotoxin stimulated guanosine 3',5'-cyclic monophosphate (cGMP) production in renal cortex, testis, and small intestinal mucosa but had only a small effect in the colon. Atrial natriuretic factor enhanced the cGMP content of renal cortex and small intestine but had no effect on testis or colon. The enterotoxin receptors were observed to be localized in proximal tubules, to epithelial cells of crypts and villi of small intestine, to crypts of colon, and in seminiferous tubules. Both convoluted and straight portions of proximal tubules exhibited specific binding sites for 125I-labeled enterotoxin. Glomeruli and distal tubules did not have receptors. Binding of 125I-enterotoxin to brush-border membranes of kidney cortex or intestinal mucosa and to testis membranes was markedly temperature dependent. The binding affinities of these receptors for E. coli enterotoxin were similar (i.e., IC50 approximately equal to 0.4-0.5 nM). Daily administration of 20 micrograms of enterotoxin intramuscularly to opossums increased urine cGMP excretion with no apparent changes in urine volume, Na+, or K+ excretion. Thus receptors for heat-stable enterotoxins are localized to proximal tubules of kidney and to enterocytes and seminiferous tubules of intestine and testis, respectively. Apical membranes may be the site of enterotoxin receptors in these epithelia.

The parathyroid glands of chickens were autotransplanted and the return of parathyroid function following transplantation was determined. Parathyroidectomy (PTX) resulted in a marked hypocalcemia (5.2 +/- 0.2 mg/dl) 4 hr following PTX. Plasma calcium (PCa) had declined to 4.3 +/- 0.2 mg/dl 24 hr after PTX. Parathyroid glands were transplanted subcutaneously 24 hr after removal and 24 hr later, PCa had risen to 8.6 +/- 0.5 mg/dl. Seven days after PTX. PCa increased to 10.3 +/- 0.2 mg/dl and by 14 days was indistinguishable from control levels (10.8 +/- 0.2 mg/dl vs. 11.0 +/- 0.2 mg/dl, respectively). When chicks with transplanted glands were fed a low Ca (0.08%) diet for 2 weeks they were able to maintain plasma PCa at levels comparable to control birds. Removal of the transplanted glands resulted in marked decreases in PCa (from 9.7 +/- 0.3 to 5.6 +/- 0.8 mg/dl), in the fractional excretion of phosphate, in urine cAMP, and in renal 25OH-vitamin D3-1 alpha-hydroxylase activity. Stepwise reductions in PCa and 1 alpha-hydroxylase activity were produced in partially PTX and fully PTX chicks by removing part or all of the parathyroid tissue. These data suggest that the transplanted parathyroid tissue was the major source of circulating PTH and that it may be possible to produce different degrees of acute hypoparathyroidism by varying the amount of transplanted parathyroid tissue removed surgically. Chickens with transplanted parathyroid glands thus provide a convenient animal model in which to study parathyroid function in an avian species.

Aspirin alters the gastric mucosal barrier as measured by ionic flux and potential difference. The effect of cimetidine on aspirin-induced alterations in gastric mucosa was studied in five normal male volunteers. Aspirin effects were studied with and without previous treatment with cimetidine. Mean (+/- SEM) basal potential difference was -48 +/- 1 mV. After 600 mg of aspirin in 1 dl of isotonic saline, potential difference decreased in 10 min to -39 +/- 1 mV (P less than 0.001) and returned to baseline within 60 min. Control biopsies showed 2% damaged mucosal cells compared with 20% damaged at the time of maximal drop in potential difference (P less than 0.001) after aspirin. Recovery to 9% damage occurred by 60 min. In subjects pretreated with 300 mg cimetidine, potential difference rose during 1 h to -62 +/- 1 mV (P less than 0.001). After aspirin potential difference fell to -48 +/- 1 mV compared with -39 +/- 1 mV with aspirin alone (P less than 0.01) and returned to -62 +/- 1 mV at 60 min. The cimetidine-treated group showed 4% mucosal damage at the peak potential difference fall after aspirin, significantly less (P less than 0.02) than in the untreated subjects.

During the middle of prenatal day 10, the opossum allantois forms as a ventral outgrowth of the hindgut. By day 11 it appears as a large, fluid filled sac and by the middle of day 12 (just prior to birth) it reaches its maximal development. The simple squamous epithelium lining the allantois consists of only one cell type that often contains numerous filaments in the apical cytoplasm. At the luminal surface, the apices of the cells are united by junctional complexes and desmosomes are present between adjacent cells. The luminal surface is irregular, whereas laterally and basally the cell membranes show few if any infoldings. Mitotic figures and presumptive degenerating cells occasionally occur in the allantoic epithelium which rests on a delicate basal lamina. The allantois is covered by a simple squamous mesothelium that lacks a distinct basal lamina. Between the two epithelial sheets lie mesenchymal cells, collagen fibers, and blood vessels. No specializations of cell membranes were noted in either of the epithelial layers. The yolk sac endoderm consists of a single layer of squamous cells whose cytoplasm contains scattered profiles of rough endoplasmic reticulum and mitochondria. Extensive lateral and basal infoldings of the plasmalemma were not observed in these endodermal cells. The morphology of the trophectodermal (trophoblastic) cells indicates a cell type that is active in the transport of materials. Since the endodermal cells that line the allantois lack morphological features that would suggest the presence of mechanisms for transport or exchange, and because they remain relatively unchanged throughout pregnancy, it is thought that the allantois functions primarily in the storage of urinary wastes during prenatal life.(ABSTRACT TRUNCATED AT 250 WORDS)

Numerous inclusion bodies (virus-like particles) were observed in the lumina of the intercellular canaliculi, mucous tubules and intralobular ducts of the opossum submandibular gland. The particles are spherical in outline, show an electron dense core, and are surrounded by a peripheral membrane.

Cardiac muscle cells in the right ventricle of the postnatal opposum were studied ultrastructurally, with particular attention to the developmental stage of T-tubule formation. Animals ranging from 5.5 cm (day 29 of postnatal life) to 41 cm (young adult) in body length were used. Typical T-tubules were first recognized in a few myocardial cells of the 7.5 cm (day 43) opossum. T-tubules increased in number as cardiac muscle cells continued to differentiate until 22 cm in body length (about 105 days after birth). At this stage of development most of the T-tubules were completely established. The general mode of differentiation and development of cardiac muscle cells appeared essentially the same as in other mammals.

At birth, the opossum lung is remarkably primitive and consists of a system of branching airways that end in a number of terminal air chambers. From the newborn through the 10 cm stage of development the conducting portion of the lung predominates. The air chambers, which represent portions of the conducting system modified for respiration, are in a constant state of evolution since they are destined to become part of the expanding bronchial system. The airways are devoid of cilia and goblet cells at birth, and are lined by columnar epithelial cells which contain two types of cytoplasmic granules: an electron-dense form and a heterogeneous form. The latter exhibits an electron-dense core surrounded initially by a large halo of flocculent material. This type of granule is not seen beyond the 8 cm stage. The terminal air chambers of the newborn and later stages are lined type I and type II alveolocytes that appear identical to the alveolocytes lining alveoli in the adult. By the 2.5 cm stage, scattered cilia are present in the trachea and bronchi and bands of smooth muscle have differentiated in relation to bronchial epithelium and to proximal areas of the terminal chambers. Citiated cells are separated by ridges composed of light and dark cells which are without cilia and which contain scattered electron-dence granules. Throughout the postnatal period numerous alveolar macrophages and mast cells are noted in relation to the conducting system and pleura. Differentiation of the pleura also occurs during the postnatal period. In the newborn the pleura is simple squamous mesothelium. Later stages develop a thick connective tissue lamina between the pleural mesothelium and lung parenchyma. A large band of elastin is interposed between the mesothelium and underlying bundles of collagen.

The duodenal glands were first observed in 1679 by Wepfer (1) who described them during the autopsy of a beheaded woman. Wepfer described their arrangement in the duodenum and observed that when they were macerated in water, the duodenal glands discharged copious amounts of mucus. Nine years later, Brunner (2,3), who was Wepfer’s son-in-law (4), described the duodenal glands in the horse, ox, sheep, deer, dog, and beaver and presented a brief description in man. Brunner considered these glands to be accessory pancreatic tissue and termed them “glandulae duodeni” or “pancreas secundarium.” Middeldorpf (5) realized that the secretion of the duodenal glands differed from that of the pancreas and suggested that these glands be designated “the glands of Brunner.” Florey and Harding (6,7) found that the region of the duodenum containing the duodenal glands is more resistant to acid erosion than other regions of the small intestine.

Male Syrian Golden-Hamsters consumed about 90% of their fluid as an ethanol-water solution when given a choice between water and ethanol-water solutions. This resulted in a daily alcohol intake of about 11 g/kg. After 53 days of alcohol ingestion there was no evidence of tolerance to the soporific effects of parenterally administered ethanol and removal of the ethanol solutions failed to produce any signs of alcohol withdrawal. However, after cessation of ethanol ingestion, the acquisition of escape responding from footshock was impaired in the alcohol group as compared to a control group. Biochemical and ultrastructural analyses demonstrated that chronic ethanol ingestion hepatic glycogen and plasma triglycerides without altering either the hepatic or plasma concentrations of phospholipids, free cholesterol or cholesterol esters. These results demonstrate that the hamster has an unusual metabolic response to ethanol. These findings are contrasted to the biochemical and behavioral effects of the drug in other species.

The Escherichia coli heat-stable enterotoxin (ST1 or STa) binds to specific receptors on mammalian intestinal brush border membranes, and stimulates guanylate cyclase in those membranes. We have found a similar signal transduction system in brush border membranes prepared from kidney cortex of the American opossum (Didelphis virginiana, and in a cell line (OK cell) derived from that tissue. Activation of guanylate cyclase by ST1 is therefore not limited to intestinal cells. Furthermore, since it is unlikely that ST1 which is produced in the intestinal lumen, would have access to kidney receptors, this suggests the existence of an endogenous peptide resembling ST1, at least in marsupials.

The air chambers of the newborn opossum are lined by a respiratory epithelium which appears similar to that lining alveoli of other species. The type II pulmonary epithelial cell is cuboidal in shape, shows apical microvilli, several Golgi complexes, lipid droplets, and numerous cytosomes. The cytosomes contain osmiophilic lamellae and are similar in appearance to whorls of osmiophilic material lying free within the alveolar lumina and on the surface of the respiratory lining epithelium. In the newborn opossum lung, examination of the air chambers with the scanning electron microscope permits the observation of several type II pulmonary epithelial cells in a single field. The potential use of the air chamber of the newborn opossum as an experimental model is suggested.

The postnatal development of Brunner's glands in the opossum has been traced, using 170 specimens divided into 21 groups according to snout-rump length. The newborn opossum has a well developed small intestine, possessing villi and a differentiated intestinal epithelium with concentrations of PAS-positive material in the apical cytoplasm. The ducts of the glands begin to develop within 24 hours after birth and, as they proliferate, two cell types appear. A tall, columnar cell type lines the excretory duct whereas the intralobular duct system is lined by pyramidal cells. Intralobular ducts undergo differentiation by the 50 mm stage and, after this event, secretory units appear as outgrowths from the intralobular duct system. Development continues into early adulthood. Duodenal glands appear to evaginate simultaneously at localized foci, resulting in the formation of a duodenal sinus between glandular elements. The glands evaginate from the mucosa in the most proximal portion of the duodenum, involving both intestinal and gastric mucosal elements. That portion of mucosa lying between the forming glands is submerged and forms the floor of the duodenal sinus. Excretory duct epithelium often lines the sinus in part. The development of Brunner's glands in the opossum is completely independent both of pyloric and intestinal glands.

The duodenal glands of four marsupial species, the kangaroo, native cat, marsupial mouse, and bandicoot, form a narrow lobular collar immediately distal to the gastrointestinal junction. In two species, the koala and wombat, the duodenal glands are diffuse and scattered along the intestinal tract distal to the gastrointestinal junction for considerable distances. The glands of all species examined empty independently into the intestinal lumen. Histochemical studies indicate that the latter two species, the koala and wombat, elaborate an acid mucin whereas the former species produce a neutral mucosubstance. Ultrastructural examination shows that generally the duodenal glands are comprised of large pyramidal cells that show a definite polarity, with basally-placed nuclei and apically-situated secretory granules. Species differences, with regard both to the morphology and nature of the secretory granules and to the proportions of cell organelles, exist. The diversity of diet between species is discussed.

Brunner's glands of the echidna form a thick, interwoven collar confined to the submucosa of the most distal portion of the stomach. The glandular mass ends immediately proximal to the pyloroduodenal junction and empties onto a surface lined by stratified squamous epithelium. Histochemical studies indicate that the secretion elaborated by the glands is an acid mucopolysaccharide. Secretory tubules in the glands consist of large, pyramidal-shaped cells resting on a delicate basal lamina. They contain large, pale or granular secretory droplets which are membrane bounded and are found in close association with extensive Golgi complexes and also at the apex of the cells. Secretary granules, occasionally fused into irregularly-shaped complexes in the apical region, appear to rupture the cell membrane and discharge their contents into the adjacent lumen. Small, dense granules are also present but less abundant. The granular endoplasmic reticulum is confined mainly to the perinuclear region and comprises dilated cisternae containing amorphous material. Several small vesicles apparently formed from smooth membrane areas of the ergastoplasm are seen adjacent to the Golgi networks. The epithelium lining the duct is devoid of large secretory granules and contains relatively few organelles.

The stomach of the suckling echidna is lined by a tall columnar epithelium that is bounded basally by a delicate basement membrane. Adjacent cells are held in close apposition by tight junctions near the apex and by extensive implications of the remaining lateral surfaces. The basal cell surface is smooth and without apparent specialization. The lining epithelium is characterized by an abundance of mitochondria and a relative paucity of other organelles. Scattered argentaffin cells extend between the bases of the gastric lining cells and rest upon the luminal side of the basement membrane. Absorptive cells lining the small intestine of the suckling echidna exhibit in-vaginations of the apical plasma membrane which branch and anastomose, forming a dense network of tubules in the apical cytoplasm. Adjacent to this network is a series of small vacuoles of varying diameters which come into direct relation with a single, large, supranuclear vacuole. The vacuolar system contains both a fine granular substance and clusters of a flocculent amorphous material thought to be of a proteinaceous nature. The surrounding cytoplasm contains numerous profiles of smooth endoplasmic reticulum, several Golgi systems, and a relative abundance of mitochondria. Clusters of homogeneous droplets are found in the cytoplasm and in the intercellular space.

This study reports the presence of caveolated cells in the duodenal glands of the white-tailed deer. Caveolated cells have not been observed previously in the duodenal glands of other species studied to date.