Absorption of arginine-vasopressin and arginine-vasotocin in small intestine of the frog Rana temporaria

Experiments in vitro demonstrated a partial absorption of arginine-vasopressin (AVP) in the frog small intestine. Dynamics and efficiency of the nonapeptide absorption are studied with use of hydroosmotic method of recording of the osmotic permeability of the frog urinary bladder epithelium and immunoenzyme analysis. In the process of absorption there were preserved intactness of the hormone cyclic structure and its physiological activity, like in the case of the arginine-vasotocin (AVT) absorption. The AVP absorption increased at its administration into the gut with inhibitor of proteases. By methods of immunoelectron and immunofluorescent microscopy with use of polyclonal antibody to AVP, location of the label to the hormone was shown in the enterocyte cytoplasm. Thus, there was obtained a morphological evidence for the AVP absorption and transepithelial transfer in the frog small intestine. These data enlarge the concept of the poorly studied properties of the absorbing epithelium of the vertebrate intestine with respect to absorption of intact molecules of polypeptides.     

Absorption of arginine-vasopressin and arginine-vasotocin in small intestine of the frog <Emphasis Type="Italic">Rana temporaria</Emphasis>

Experiments in vitro demonstrated a partial absorption of arginine-vasopressin (AVP) in the frog small intestine. Dynamics and efficiency of the nonapeptide absorption are studied with use of hydroosmotic method of recording of the osmotic permeability of the frog urinary bladder epithelium and immunoenzyme analysis. In the process of absorption there were preserved intactness of the hormone cyclic structure and its physiological activity, like in the case of the arginine-vasotocine (AVT) absorption. The AVP absorption increased at its administration into the gut with inhibitor of proteases. By methods of immunoelectron and immunofluorescent microscopy with use of polyclonal antibody to AVP, location of the label to the hormone was shown in the enterocyte cytoplasm. Thus, there was obtained a morphological evidence for the AVP absorption and transepithelial transfer in the frog small intestine. These data enlarge the concept of the poorly studied properties of the absorbing epithelium of the vertebrate intestine with respect to absorption of intact molecules of polypeptides.     

Membrane domains of intestinal epithelial cells: distribution of Na+,K+- ATPase and the membrane skeleton in adult rat intestine during fetal development and after epithelial isolation

The organization of the basolateral membrane domain of highly polarized intestinal absorptive cells was studied in adult rat intestinal mucosa, during development of polarity in fetal intestine, and in isolated epithelial sheets. Semi-thin frozen sections of these tissues were stained with a monoclonal antibody (mAb 4C4) directed against Na+,K+-ATPase, and with other reagents to visualize distributions of the membrane skeleton (fodrin), an epithelial cell adhesion molecule (uvomorulin), an apical membrane enzyme (aminopeptidase), and filamentous actin. In intact adult epithelium, Na+,K+-ATPase, membrane-associated fodrin, and uvomorulin were concentrated in the lateral, but not basal, subdomain. In the stratified epithelium of fetal intestine, both fodrin and uvomorulin were localized in areas of cell-cell contact at 16 and 17 d gestation, a stage when Na+,K+-ATPase was not yet expressed. These molecules were excluded from apical domains and from cell surfaces in contact with basal lamina. When Na+,K+-ATPase appeared at 18-19 d, it was codistributed with fodrin. Detachment of epithelial sheets from adult intestinal mucosa did not disrupt intercellular junctions or lateral cell contacts, but cytoplasmic blebs appeared at basal cell surfaces, and a diffuse pool of fodrin and actin accumulated in them. At the same time, Na+,K+-ATPase moved into the basal membrane subdomain, and extensive endocytosis of basolateral membrane, including Na+,K+-ATPase, occurred. Endocytosis of uvomorulin was not detected and no fodrin was associated with endocytic vesicles. Uvomorulin, along with some membrane-associated fodrin and some Na+,K+-ATPase, remained in the lateral membrane as long as intercellular contacts were maintained. Thus, in this polarized epithelium, interaction of lateral cell-cell adhesion molecules as well as basal cell-substrate interactions are required for maintaining the stability of the lateral membrane skeleton and the position of resident membrane proteins concentrated in the lateral membrane domain.     

Tenascin,E-cadherin and P2X calcium channel receptor expression is increased during rat blastocyst implantation

The calcium-activated cell-adhesion proteins tenascin, E-cadherin and the purinergic (P2X) calcium channel receptors are expressed in an identical spatial and temporal pattern in uterine epithelium in the rat during implantation. On Day 1 of pregnancy (estrous), a diffuse cytoplasmic and specific basement membrane label for each of the proteins was observed throughout the uterine epithelium. On Day 3 of pregnancy, a specific and prominent lateral plasma membrane label for each protein was seen. At the time of implantation on Day 6, an additional and significant increase in the label for each was observed on the apical epithelium. At this time, the label for tenascin in the apical epithelium was increased 2.1-fold (p < 0.0004), that of E-cadherin was increased 2.5-fold (p < 0.0001) and the P2X receptor label was increased 2.0-fold (p < 0.0001). These observations suggest a major role for the calcium-activated adhesion proteins tenascin and E-cadherin in attachment and implantation, with ionic calcium for protein activation possibly provided by the P2X calcium channels. These events occur along the entire length of the uterine epithelium in preparation for blastocyst adhesion.     

Rat intestinal galactoside-binding lectin L-36 functions as a structural protein in the superficial squamous cells of the esophageal epithelium

Using an affinity purified antibody raised against the RI-H fragment of rat intestinal lectin L-36, the latter protein has been identified within the esophageal epithelium by means of ultracryotomy followed by immunogold labeling. The epithelium consists of 4 morphologically distinct cell-types, namely, the basal, spiny, granular and squamous cells, and each of these exhibits a different immunolabeling pattern. The basal cells form a layer on the basal lamina, and in these a diffuse cytoplasmic staining is observed. This basal cell layer is overlaid by spiny cells that extend many cell processes into wide intercellular spaces. In these cells, immunogold particles are found only on small granular inclusions consisting of an electron-lucent homogeneous substance. The granular cells from a third layer over the spiny cells, and are characterized by a number of large granular inclusions with an electron-dense core rimmed by a less electron-dense substance. Immunogold labeling is found on these granules, both on the core and peripheral region. Squamous cell-types constitute the most superficial layer of the epithelium. They are without granular inclusions, and immunogold labeling is confined to the cytoplasmic surface of the thickened plasma membrane. These findings suggest that L-36 is produced in the basal cells as free cytosolic protein, then becomes progressively aggregated into the granular inclusions of the spiny and granular cells, and is eventually transferred onto the cytoplasmic surface of the squamous cell plasma membrane where it may interact with complementary glycoconjugate(s) located at this site. The membrane lining substance thus formed may play a role in stabilizing the squamous cell membranes, thereby maintaining the structural integrity of the epithelium against mechanical stress coming from the esophageal lumen.     

Close relationships between the cells of the immune system and the epithelial cells in the rat small intestine

Summary A possible contribution of the intestinal epithelium to the immune defence system was studied by electron microscopy in the rat small intestine. The cells of the immune system (CIS) such as lymphocytes, eosinophils and macrophages penetrate the basal lamina into the epithelium and make close relationships with the absorptive cells. At the points of close apposition, the two cell membranes run parallel at a regular distance of about 20 nm. On the other hand, about 5% of the intestinal absorptive cells also penetrate the basal lamina into the lamina propria via their basal protrusions and show a similar close association with CIS. The basal protrusions contain many microfilaments; this indicates that they are structures with a definite function rather than a simple hernia. These findings are discussed with respect to the transport of antigenic molecules and of intercellular communication between CIS and the intestinal epithelium.     

Arginine-vasopressin immunoreactive material in the gastrointestinal tract

Summary Like many other neuropeptides, vasopressin is not confined to the hypothalamic neurohypophysial system. Furthermore, vasopressin was found to be a potent vasoconstrictor in the rat jejunum, reducing myenteric artery flow. These associations were the basis of this investigation on the presence of vasopressin in the gastrointestinal (GI) tract by both RIA and immunohistochemistry.Portions of the gastrointestinal tract and pancreatic islets of the rat were extracted with 0.1N HCl for RIA measurements of AVP content. Similar portions from the male cat GI tract were used for immunohistochemistry studies.Acid extracts of the GI tract were found to contain immunoreactive AVP with the highest concentration (pg/mg protein) in the fundus portion of the stomach (15.0±1.6) and slightly lower values down along the antrum-pylorus portion (6.7±0.6), proximal jejunum (8.6±0.2), distal ileum (9.7±0.3) and colon (11.9±0.5). In the pancreatic islets the concentration was much higher (72.0 pg/mg protein). The extract inhibition curves showed parallelism with the appropriate standard preparation of AVP in the specific RIA.Immunohistochemical localization showed IR-AVP in the nerve fibers around the myenteric plexus of the second portion of the duodenum. It was also found in fibers starting from where the myenteric plexus goes through the layer of muscle fibers, penetrating the submucosa and duodenal mucosa, ending near the capillaries situated along the basal side of the villous epithelium cells. Similar IR-AVP activity was found in cells located in the mucosal epithelium of the duodenum, jejunum, ileum, colon and rectum.These results show that the gastrointestinal tract of different species and pancreatic islets of the rat are a rich source of immunoreactive neurohypophysial AVP. Because of its distribution, this peptide might have some physiological significance in intestinal circulatory regulation.     

Estimation of oral drug absorption in man based on intestine permeability in rats

Predicting the fraction of an oral dose absorbed in humans is of considerable interest at an early stage of a research program in the pharmaceutical industry. Models described in the literature to predict the oral absorption in man include: the permeability in Caco-2 cells, absorption from a perfused segment of rat intestinal lumen and uptake into everted rings. The present study used an isolated and vascularly perfused rat small intestine to determine the permeability values of eleven compounds across the intestinal epithelium. A good correlation was obtained between the permeability values determined in this model and the proportion of an oral dose absorbed in humans. Compared to the other models, the present one could allow the appearance in the artificial bloodstream and the intestinal metabolism of a compound to be studied simultaneously.     

SECRETION OF COLLAGEN BY CORNEAL EPITHELIUM : I. Morphology of the Collagenous Products Produced by Isolated Epithelia Grown on Frozen-Killed Lens

Corneal epithelium from 5–7-day old chick embryos was isolated with EDTA and grown in culture on frozen-killed lens as a substratum. Autoradiographs showed that in the presence of [³H]proline, the corneal epithelium synthesized and secreted onto the lens substratum, radioactive materials resistant to extraction by sodium hydroxide. The radioactive label was associated with newly formed striated collagen fibrils, large "sheets" of collagen, and basal lamina. The repeat period and interband pattern of the abundant new collagen sheets and fibrils was typical of "native" or so-called "mesenchymal" collagen. Collagen-like materials were observed in secretory (Golgi) vacuoles within the corneal cells and collagen fibrils within the intercellular canals (lateral interfaces) of the epithelium, as well as at the base of the cells. Both the granular endoplasmic reticulum and Golgi complexes were highly developed in the corneal epithelium. In the discussion, the role of cytoplasmic organelles in collagen secretion, the origin and structure of the basal lamina, and variations in collagen polymerization patterns in vitro are reviewed and evaluated. The morphogenetic significance of the synthesis and secretion of collagen by embryonic epithelium is appraised and the production of true native-striated collagen by epithelium is stressed.     

Identification of the V1 vasopressin receptor by chemical cross-linking and ligand affinity blotting

Chemical and photoaffinity cross-linking experiments as well as ligand affinity blotting techniques were used to label the V1 vasopressin receptor. In order to determine the optimal reaction conditions, pig liver membranes were incubated with 5 nM [8-lysine]vasopressin (LVP) labeled with 125I and then cross-linked with the use of DMS (dimethyl suberimidate), EGS [ethylene glycol bis(succinimidyl succinate)] or HSAB (hydroxysuccinimidyl p-azidobenzoate) at different final concentrations. Consistently, EGS was found to label with high yield one band of Mr 60,000 in rat and pig liver membranes when used at a final concentration between 0.05 and 0.25 mM. The protein of Mr 60,000 is labeled in a concentration-dependent manner when pig liver membranes are incubated with increasing concentrations of 125I-LVP and then cross-linked with EGS. The label was displaced by increasing concentrations of unlabeled LVP or d(CH2)5 [Tyr2(Me),-Tyr9(NH2)]AVP (V1/V2 antagonist). A protein band of similar molecular mass was cross-linked with 125I-LVP in rat liver membranes. The reaction was specific since the incorporation of label into the protein of Mr 60,000 was inhibited by LVP, [8-arginine]vasopressin (AVP), the V1/V2-antagonist, and the specific V1-antagonist d(CH2)5 [Tyr2(Me)]AVP, only partially by [des-Gly9]AVP (V2-agonist) and by oxytocin, and not at all by angiotensin II. Incubation of nitrocellulose containing membrane proteins from pig liver with 125I-LVP showed the labeling of a band of Mr 58,000 that is inhibited by an excess of unlabeled LVP. This band of Mr 58,000 seems to correspond with the protein of Mr 60,000 revealed by the cross-linking experiment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ultrastructural localization of acid phosphatase in nonhuman primate vaginal epithelium

Summary The vagina of the rhesus monkey is lined by a stratified squamous epithelium. However, little is known regarding the cytochemical composition of its cell organelles and the substances found in the intercellular spaces. In this study we have examined the ultrastructural distribution of acid phosphatase in the vaginal epithelium. In basal and parabasal cells reaction product was found in some Golgi cisternae and vesicles and in a variety of cytoplasmic granules. Reaction product was also found in some, but not all, membrane-coating granules. In the upper layers of the epithelium, the membrane-coating granules extruded their contents and acid phosphatase was localized in the intercellular spaces. The possible roles of acid phosphatase in keratinization, desquamation, or modification of substances in the intercellular compartment are discussed.     

Tissue distribution of pneumadin immunoreactivity in the rat

Pneumadin (PNM) is a decapeptide, originally isolated from mammalian lungs, which exerts a potent stimulating effect on arginine-vasopressin (AVP) release, thereby evoking an antidiuretic effect. We have established a specific radioimmunoassay (RIA) method for rat PNM determination, the sensitivity of which is sufficient for measuring tissue content of the peptide. Moreover, raised antibodies have been used for the immunocytochemical detection of PNM in several rat organs. As expected, high concentrations of PNM were detected by RIA in newborn and adult rat lungs and immunocytochemistry (ICC) localized PNM immunoreactivity (IR) in the bronchial and bronchiolar epithelium. Very high concentrations of PNM were measured by RIA in the prostate, and ICC showed that PNM-IR is contained in the epithelial cells. RIA and ICC demonstrated the presence of low amounts of PNM in the thymus. The highest content of radioimmunoassayable PNM was found in the kidneys and intestinal tract, but dilution test suggested the presence of some interfering substances in these tissues. Accordingly, ICC-detectable PNM-IR was absent in the kidneys and present only in the duodenal criptae and Brunner's glands of the intestinal tract. RIA did not measure sizeable PNM concentrations in the thyroid gland, but ICC showed PNM-IR in C-cells. RIA and ICC did not detected PNM in testes, seminal vesicles, ovaries, uterus, pancreas, liver, spleen, adrenal glands, and heart. Taken together, our findings suggest that PNM, in addition to its role as hypothalamo-pituitary AVP secretagogue, may be involved in the autocrine-paracrine functional regulation of other peripheral organs, like lungs and prostate and perhaps duodenum, thymus and thyroid gland.     

Electron microscopic observations on the maintenance of the tight junction during cell division in the epithelium of the mouse small intestine.

Dividing epithelial cells in the mouse small intestine were examined by thin-section electron microscopy with special attention given to the mode of cytokinesis. As the columnar epithelial cells entered mitosis in the crypt, they became rounded, maintaining their junctional complexes with neighboring cells while detaching themselves from the basal lamina. In such rounded cells the mitotic apparatus was formed with its long axis parallel to the luminal surface. Replicated centrioles moved down from the apical region to locate themselves lateral to the nucleus, where they served as the poles of the mitotic spindle. During mitosis the cell retained microvilli on its luminal surface, though the terminal web became much thinner. At telophase the formation of a cleavage furrow proceeded asymmetrically from the basal side alone, and thus the contractile ring which was prominent at the base of the furrow, merged with the terminal web. Eventually, an intercellular bridge with a midbody was formed on the luminal surface. The space in the furrow was occupied by the flattened cytoplasmic processes of the neighboring cells. The tight junction was also seen on the basolateral surface of the intercellular bridge with the underlying neighboring cells. At very late telophase the intercellular bridge was disconnected from the neighboring cells and protruded into the lumen. These observations have led us to propose a mode by which the simple columnar epithelium maintain the tight junctional seal during cell division in the crypt of the small intestinal epithelium.     

The mechanism of epithelial shedding after ischemic damage to the small intestinal mucosa

The intestinal mucosa of the rat was examined by light and electron microscopy 15, 30, 60 and 120 min after complete ligation of the vessel arcades of the proximal jejunum. The characteristic sign of ischemic damage to the small intestinal mucosa and the reason for epithelial shedding is the appearance of membrane enclosed cytoplasmic blebs which arise at the cell base of the enterocytes and detach the epithelium from the basement membrane. This process begins at the tip of the villi before the enterocytes display signs of irreversible damage and progress to the base of the villi with continuation of the ischemia.     

Intestinal carbonic anhydrase, bicarbonate, and proton carriers play a role in the acclimation of rainbow trout to seawater

Abrupt transfer of rainbow trout from freshwater to 65% seawater caused transient disturbances in extracellular fluid ionic composition, but homeostasis was reestablished 48 h posttransfer. Intestinal fluid chemistry revealed early onset of drinking and slightly delayed intestinal water absorption that coincided with initiation of NaCl absorption and HCO(3)(-) secretion. Suggestive of involvement in osmoregulation, relative mRNA levels for vacuolar H(+)-ATPase (V-ATPase), Na(+)-K(+)-ATPase, Na(+)/H(+) exchanger 3 (NHE3), Na(+)-HCO(3)(-) cotransporter 1, and two carbonic anhydrase (CA) isoforms [a general cytosolic isoform trout cytoplasmic CA (tCAc) and an extracellular isoform trout membrane-bound CA type IV (tCAIV)], were increased transiently in the intestine following exposure to 65% seawater. Both tCAc and tCAIV proteins were localized to apical regions of the intestinal epithelium and exhibited elevated enzymatic activity after acclimation to 65% seawater. The V-ATPase was localized to both basolateral and apical regions and exhibited a 10-fold increase in enzymatic activity in fish acclimated to 65% seawater, suggesting a role in marine osmoregulation. The intestinal epithelium of rainbow trout acclimated to 65% seawater appears to be capable of both basolateral and apical H(+) extrusion, likely depending on osmoregulatory status and intestinal fluid chemistry.     

Rat testis motor proteins associated with spermatid translocation (dynein) and spermatid flagella (kinesin-II)

In this study, we report sites in the seminiferous epithelium of the rat testis that are immunoreactive with antibodies to the intermediate chain of cytoplasmic dynein and kinesin II. The study was done to determine whether or not microtubule-dependent motor proteins are present in Sertoli cell regions involved with spermatid translocation. Sections and epithelial fragments of perfusion-fixed rat testis were probed with an antibody (clone 74.1) to the intermediate chain of cytoplasmic dynein (IC74) and to kinesin-II. Labeling with the antibody to cytoplasmic dynein was dramatically evident in Sertoli cell regions surrounding apical crypts containing attached spermatids and known to contain unique intercellular attachment plaques. The antibody to kinesin II reacted only with spermatid tails. The levels of cytoplasmic dynein visible on immunoblots of supernatants collected from spermatid/junction complexes treated with an actin-severing enzyme (gelsolin) were greater than those of controls, indicating that at least some of the dynein may have been associated with Sertoli cell junction plaques attached to spermatids. Results are consistent with the conclusion that an isoform of cytoplasmic dynein may be responsible for the apical translocation of elongate spermatids that occurs before sperm release. Also, this is the first report of kinesin-II in mammalian spermatid tails.     

Activation of phospholipase C and prostaglandin synthesis by [arginine]vasopressin in cultures.

[Arginine]vasopressin (AVP) stimulates maximal prostaglandin E2 production in cultured rat renal mesangial cells within 2 min. As early as 10s after addition of AVP (10(-6)M) a significant loss of radioactivity from phosphatidylinositol 4,5-bisphosphate but not from phosphatidylinositol 4-phosphate and phosphatidylinositol was observed in cells prelabelled with 32Pi. Cells labelled with [14C]arachidonic acid showed an increase of label in 1,2-diacylglycerol after 15 s and in phosphatidic acid after 30 s upon stimulation with AVP. Pretreatment of the cells with indomethacin (10(-5)M) did not abolish the effect of AVP on the increased labelling of phosphatidic acid.     

Immunolocalization of Protein 4.1B in the Rat Digestive System

Protein 4.1 family proteins are thought to interact with membrane proteins and also membrane skeletons. In this study, immunohistochemical studies by light and electron microscopy were performed with a specific antibody against protein 4.1B. Specific protein 4.1B immunolabeling was observed in simple columnar epithelium in the adult rat large intestine, small intestine and stomach. Protein 4.1B immunolabeling was localized along the membranes facing the adjacent cells (lateral portion) and also facing the extracellular matrix (basal portion). Moreover, a spatial protein 4.1B expression gradient was observed along the crypt-villus axis of the rat small and large intestinal epithelium: strong protein 4.1B expression was present within the villus, with the crypt showing barely any detectable protein 4.1B. The expression of protein 4.1B was not detected in the stratified squamous epithelium in the forestomach or the esophagus. By immunoelectron microscopy, the immunolabeling of the cells was observed to be restricted to the cytoplasmic side just beneath the plasma membrane, including the membranes adjacent to the next cells, except for the tight junctions. We conclude that the protein 4.1B expression pattern is related to the maturation of simple columnar epithelium in the rat digestive system, probably by the effect of adhesion.     

Spontaneous51Cr release by isolated rat hepatocytes: An indicator of membrane damage

Summary Radiochromium uptake and release by isolated rat hepatocytes in suspension was monitored under continuous-labeling conditions. Cell protein remained unchanged during the absorption phase, whereas the release of⁵¹Cr correlated well with the loss of cell viability and release of cytoplasmic protein. The results suggest that under equilibrium conditions,⁵¹Cr release represents an efflux of label from damaged or dying preparations and not an elution of radioisotope from intact cells.     

Enhancement of rat intestinal calcium absorption by vanadate.

Vanadate alters intestinal transport and may have a role in regulating cell function. To determine whether it influences calcium absorption, we tested the effects of acute and chronic vanadate administration on calcium absorption using single-pass perfusion of jejunal and ileal segments of the in vivo rat intestine. Acute vanadate administration increased the lumen-to-mucosa and net fluxes of calcium in both the jejunum and ileum. The increase was largely due to an enhancement of the saturable fluxes of calcium and was observed at 10(-4) M concentration of vanadate, but not at higher or lower concentrations of the oxyanion, except at the highest concentration used, 10(-2) M, where calcium absorption was inhibited. Chronic vanadate administration caused, on the other hand, no changes in calcium absorption. We have demonstrated previously that rat intestinal (Na+ + K+)-ATPase is inhibited by vanadate, an effect that could raise cell sodium and increase the efflux of sodium across the brush border membrane. The results suggest that the vanadate enhancement of calcium absorption may be related to an increased entry of calcium into the mucosa, possibly as a result of an augmented exchange through the Na+/Ca+ antiport system. Alternatively, vanadate may influence access to a calcium channel in the mucosal membrane of the intestinal epithelium, leading to the observed increase in absorption.