Localization of carbonic anhydrase activity in the developing rat colon

Prenatal development and histochemical characteristics of gastrointestinal mucins in sheep fetuses

The object of this study was to describe the prenatal development and histochemical properties of mucins in the sheep gastrointestinal tract. To determine changes in the mucin profile, the sections were stained with specific histochemical stains for carbohydrates. While neutral and mixed mucins were observed in the superficial epithelial cells of the abomasal pyloric region, acidic mucins were detected in the secretory ducts and corpus of the glands. Acidic mucins consisted predominantly of sialomucins. In the duodenal villi, the number of goblet cells containing neutral mucins increased toward the end of gestation, whereas Brunner's glands contained acidic mucins until the 95th day of gestation and both acidic and neutral mucins thereafter. The jejunal goblet cells contained either acidic, neutral, or mixed mucins. Goblet cells containing acidic mucins, which were mainly localized to the ileal crypts and villi, mostly contained sulfated mucins. While villi were observed in the proximal colon until the 115th day of gestation, later the typical crypt structure emerged. During the period in which the villi were found in the proximal colon, the goblet cells containing sulphomucins were predominant, whereas the goblet cells containing sialomucins were predominant after the typical crypt structure was formed. In conclusion, gastrointestinal mucins may be involved in the formation of meconium during the prenatal period, and acidic mucins may contribute to the strength of the intestinal barrier against pathogens and digestive enzymes, as the barrier is not fully functional after birth.

Immunohistochemical localization of carbonic anhydrase isoenzymes in salivary gland and intestine in adult and suckling pigs

Localizations of carbonic anhydrase isoenzymes (CA I, CA II and CA III) were investigated immunohistochemically in the salivary glands and intestine of mature and suckling pigs. Carbonic anhydrase isoenzymes were not detected in the salivary glands of sucklings, but were present in the adult. Bicarbonate ion in saliva might be important for the digestion of solid foods in mature pigs, but unnecessary for the digestion of milk in sucklings. Expressions of CA I and CA II were detected strongly in the large intestine of the adult and sucklings, and faintly only at duodenum in the small intestine. CA I and CA II isoenzymes in the large intestine may be involved, at least in part, in ion absorption and water metabolism during digestion and absorption of milk in suckling pigs. In addition, CA I and CA II expression in the duodenal villus enterocyte may support the process of bicarbonate absorption in the duodenum.

Carbonic anhydrase I and II as a differentiation marker of human and rat colonic enterocytes

Carbonic anhydrase (CA) is an enzyme that is expressed in the intestine and catalyzes the reversible hydration of CO2 in the following reaction: CO2 + H2O<==>H2CO3<==>H(+)+HCO3-. To elucidate the association of CA expression with the differentiation of colonic enterocytes, we investigated the expression and localization of CA using a Northern blotting analysis, Western blotting analysis, and immunohistochemical staining. A Northern blotting analysis revealed an abundant expression of CA I and II mRNA in the colonic epithelial cells. However, the expression of CA III mRNA was not detected. According to the results of immunohistochemical staining of the human colonic mucosa using antisera against CA I and II, both CA I and II were localized on the cytoplasm of non-goblet columnar cells in the upper half of the crypts where more differentiated cells are located. According to the results of immunohistochemical staining of the rat colonic mucosa, neither CA I and II were detected at the new-born stage. The expression of CAs in the upper half of the crypts began to rise from 1 week after birth, and thereafter increased according to the growth of the rats. At 3 weeks after birth, the expression of CAs was almost the same as that of the adult rats. The amount of CA proteins evaluated by a Western blotting analysis revealed that the expression of CAs increased gradually until reaching a maximum level at 6 or 8 weeks. These results therefore suggest that CA I and II appear to be good markers for the differentiation of enterocytes in the colonic mucosa.

Functional role of bicarbonate in propionate transport across guinea-pig isolated caecum and proximal colon

1. Unidirectional fluxes of propionate across isolated epithelia from the guinea-pig caecum and proximal colon were measured under short-circuit current conditions. In the caecum and proximal colon the serosal-to-mucosal propionate flux (JPrsm) was higher than mucosal-to-serosal flux (JPrms), resulting in a net secretory flux of propionate. 2. HCO3(-)-CO2-free solution reduced JPrms in the caecum and proximal colon markedly; JPrsm was not (caecum) or little (proximal colon) affected. The subsequent addition of acetazolamide caused a further decrease in JPrms in the proximal colon, but not in the caecum. 3. In HCO3(-)-containing solutions acetazolamide or ethoxzolamide inhibited JPrms; JPrsm was not affected. A macromolecular carbonic anhydrase inhibitor, prontosil-dextran, had no effect on propionate fluxes, indicating that the intracellular carbonic anhydrase is of importance for short-chain fatty acid transport. 4. Subsequent to carbonic anhydrase inhibition, mucosal addition of amiloride caused a slight further decrease of JPrms in the caecum and proximal colon; JPrsm was not affected. 5. Results support the view that a considerable proportion of short-chain fatty acids (SCFAs) is absorbed via a SCFA(-)-HCO3- exchange.

Morphological changes and cellular proliferation in mouse colon during fetal and postnatal development

To document regional structural and cellular proliferation changes in the developing mouse colon, tissues from fetal, suckling, and weanling mice were analyzed by light microscopy (LM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), [3H]-thymidine incorporation studies, and radioautography. The proximal and distal colon were studied independently at all ages. At 17-18 days of gestation, the mouse proximal colonic mucosa was projected into high and low longitudinal folds disposed in a V-shaped pattern. From birth up to 9 days, the mucosal folds observed by SEM can easily be misinterpreted as being a succession of high and low villus-like structures at LM level. TEM study confirmed the presence of highly specialized absorptive cells in the upper halves of the mucosal folds during this period. No recognizable crypts were noted at birth. Instead, LM and radioautography showed the presence of cell aggregates developing at the base of the epithelium at all levels of the mucosal folds. These cell aggregates evolved into rudimentary crypts giving fully differentiated crypts by day 16 with radiolabeled cells located in the midcrypt portion. As opposed to the proximal segment, a flat mucosa interspersed with well defined short crypts at birth was observed in the distal colon. During the following days, crypts further developed and by 16 days, the radiolabeled epithelial cells were still exclusively located at the base of the crypt. TEM observations illustrated that specialized cells as those found in the proximal segment did not differentiate in this segment.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of transforming growth factor alpha in the developing rat colon

BACKGROUND

Transforming growth factor alpha (TGF-alpha) is a 50-amino acid polypeptide that has been related to cell proliferation and differentiation.

METHODS

Proximal and distal colon from fetal, newborn, and adult rats were studied by immunohistochemical techniques using a monoclonal antibody against human and rat TGF-alpha.

RESULTS

Immunoreactive TGF-alpha (IR-TGF-alpha) first appeared in distal colon at 18 days of gestation when the proximal colon remained negative. At all ages studied, the staining for TGF-alpha at the base of the crypts in the distal colon showed a supranuclear pattern. At 22 days of gestation and until 9 days of postnatal development, the proximal colon is negative for TGF-alpha. From day 10 to 24 of postnatal development, IR TGF-alpha cells with a cytoplasmic staining were confined to the lower half of the villi. Afterwards, cells at the crypts showed supranuclear staining and cells in the surface epithelium a cytoplasmic reaction.

CONCLUSIONS

Age- and region-dependent expression of TGF-alpha in the rat colon suggests a functional role for TGF-alpha in the establishment and maintenance of proliferation and differentiation during development.

Morphogenesis in the fetal rat proximal colon: effects of cytochalasin D

Two major morphogenetic events, epithelial conversion and fold formation, occur in the proximal rat colon during the last week of gestation. To evaluate the role of actin microfilaments in these two developmental processes, explants from the proximal colon of 19 day fetal rats were cultured in the presence of vehicle (0.1% dimethylsulfoxide), 0.1, 1.0, or 10 micrograms/ml of cytochalasin D (CD) for 24-48 hr. Explants as well as 19, 20, and 21 day in vivo controls were prepared for light, fluorescence, and electron microscopy. The distribution of actin filaments was determined by rhodamine-conjugated phalloidin binding and ultrastructural analysis of tissue fixed in the presence of tannic acid. Prior to fold formation, phalloidin binding was enhanced along the entire epithelial-mesenchymal interface. At the onset of fold formation, focal areas of intense fluorescence appeared at irregular intervals along the base of the stratified epithelium. Within 1 day, these focal intensities were localized at the apex of small forming folds. Additional changes occurring at the epithelial-mesenchymal interface in association with fold formation included: 1) ruffling of the previously smooth basal lamina, 2) a shape change in the subjacent mesenchymal cells from elongate to cuboidal along with the appearance of numerous processes abutting the basal lamina, and 3) a unique orientation of the associated collagen fibrils in some presumptive folds. Fold formation was inhibited in > 93% of explants cultured in the presence of 1.0 micrograms/ml CD. These explants appeared to be arrested precisely at the onset of fold formation. Epithelial conversion was also incomplete in these explants. These findings indicate an active role for actin in both fold formation and epithelial conversion.

Structural and enzymatic changes during colonic maturation in the fetal and suckling rat

To assess correlations between cellular differentiation and enzymatic maturation in the developing rat colon, tissue from fetal, suckling, weanling, and adult rats was analyzed by electron microscopy and assayed for lactase, alkaline phosphatase, and sodium-potassium-stimulated adenosine triphosphatase activities. The proximal and distal colon were analyzed independently at all ages. All three enzymes were detected in the fetal colon when the cells were highly undifferentiated. Postnatally, significant regional differences in cellular ultrastructure appeared, only some of which were directly paralleled by enzymatic changes. Each enzyme had a distinct region-specific developmental pattern. Lactase and sodium-potassium-stimulated adenosine triphosphatase were significantly enhanced at birth, decreasing to adult levels by 15 days postnatal. Regional differences were present, but the patterns were similar. These patterns did not parallel the increase in microvillar height and number and basolateral interdigitations of the surface columnar cells, the structural correlates of lactase, and sodium-potassium-stimulated adenosine triphosphatase, respectively. In contrast, developmental changes in alkaline phosphatase activity paralleled structural maturation, at least in part. The activity levels in the distal colon did not change significantly with age and few major structural changes were noted. In the proximal colon, activity increased markedly after birth, and after 10 days decreased rapidly to adult levels, a pattern that coincided with the transient appearance of villi and specialized cells with apical tubules and vesicles known to have alkaline phosphatase activity. The results show age- and region-related changes in cellular ultrastructure and enzymatic activities, only some of which appear to be directly correlated.

Cellular proliferation in proximal and distal rat colon during 1,2-dimethylhydrazine-induced carcinogenesis

Sequential changes in proliferative parameters in proximal and distal colonic crypts were studied during 1,2-dimethylhydrazine-induced carcinogenesis using [3H]thymidine autoradiography as a probe. 1,2-dimethylhydrazine (20 mg/kg) and vehicle (ethylenediaminetetraacetic acid) control rats received weekly s.c. injections for 20 wk. All animals received a pulse of [3H]thymidine before death at weeks 2, 6, 10, 16, 22, 26, or 30. In addition, 8 animals unexposed to 1,2-dimethylhydrazine or vehicle served as baseline controls. Dramatic regional differences were noted in the baseline controls. Crypt length, labeling index, and proliferative zone size were all significantly greater distally than proximally (p less than 0.05), whereas the labeling index of the proliferative zone tended to be enhanced proximally. During 1,2-dimethylhydrazine treatment the crypt length, labeling index, and proliferative zone size increased in both regions. As these parameters changed in parallel, the differences between proximal and distal colon did not change significantly during carcinogenesis. Actual tumor formation did differ, however, with tumors appearing earlier and in greater abundance in the distal colon. These findings show similar proliferative changes in both the proximal and distal colon during 1,2-dimethylhydrazine treatment and indicate that the enhanced baseline proliferative state of the distal colon compared with the proximal colon must be considered in the process of tumor formation.

Distribution and changes of glycoconjugates in rat colonic mucosa during development. A histochemical study using lectins

A study was made of the modifications of glycoconjugates in rat colonic mucosa during development. Sections of the caecum, and proximal and distal portions of the colon from Sprague Dawley rats at different stages of development (embryos, fetuses, suckling, weaning and adult rats) were examined. The sections were incubated with a battery of eight fluoresceinated lectins: DBA, SBA, WGA, LFA, PNA, GS-I, UEA-I and Con A. Some sections were treated with neuraminidase, and others were submitted to sequential saponification-neuraminidase treatment prior to incubation with the lectin (WGA, PNA or LFA). The intensity of the fluorescence was evaluated and graded from absent (-) to very positive (4+). Gradual and progressive changes were seen in colonic glycoconjugates during development. These changes revealed a unique developmental pattern for each lectin, which was independent for each cellular compartment (goblet cells, luminal surface and supranuclear region). Local and regional differences, observed between the different colonic sections, were already present from early stages of development. Moreover, our study showed that for several glycoconjugates, the differentiation process in colonic mucosa began in the distal region and continued through to the proximal region, the former being the first to reach the adult pattern. In the caecum, some lectins maintained a fetal pattern throughout all the periods of development up to the adult stage.

Lectin binding patterns in developing rat colon

To evaluate qualitative changes in brush-border and goblet cell glycoconjugates during colonic development, rhodamine-conjugated lectins were applied to tissue from fetal (18-22 day), suckling (1-20 day), and weanling (22-26 day) rats. Tissue from the proximal and distal colon of each animal was incubated with Triticum vulgaris, Arachis hypogaea, Glycine max, or Ulex europeus agglutinin I. Formalin-fixed paraffin sections and unfixed frozen sections were coded, read blindly, and graded from negative (-) or weak (+) to intensely positive (4+). The results showed a unique developmental pattern for each lectin, although in all cases the adult binding pattern was established by weaning. Alterations in the binding pattern between paraffin and frozen sections were noted only for Arachis hypogaea and Glycine max. Minimal Glycine max binding was seen at any age in paraffin sections, although in frozen sections a weak but consistent supranuclear binding was seen in goblet cells of postnatal animals. In contrast, both the brush-border and goblet cells were intensely fluorescent after exposure to Triticum vulgaris. This fluorescence was present in both regions at all ages studied. Ulex europeus agglutinin I also labeled goblet cells in the fetal and neonatal colon, but late in the suckling period regional differences appeared. This resulted in a significant loss of labeled goblet cells distally and a restriction of Ulex europeus agglutinin I-positive cells to the base of the crypts proximally. Finally, Arachis hypogaea showed a transient brush-border binding in paraffin sections of the proximal colon before weaning, whereas frozen sections revealed a supranuclear localization in goblet cells in both regions after birth. These studies indicate significant changes in membrane-associated and goblet cell secretory glycoconjugates in the developing rat colon.