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R Calvert

Publications and source records attributed to R Calvert.

At least 55 records · Page 3Linked to original sources
PubMed1985

Influences of dexamethasone on the maturation of fetal mouse intestinal mucosa in organ culture.

The effects of glucocorticoids on the maturation of the fetal small intestinal mucosa have been studied using duodenal explants resected at 17 days of gestation and cultured in a serum-free medium in the presence or absence of dexamethasone (30-300 ng/ml). Dexamethasone (a) increases specifically alkaline phosphatase, maltase, trehalase and sucrase activities and (b) allows an accumulation of goblet cells along the villi at a faster rate than that occurring in utero. These results indicate that glucocorticoids influence directly the differentiation of absorptive cells and goblet cells in the small intestine during the fetal period.

Alkaline Phosphatase↗
PubMed1985

Dietary fiber and intestinal adaptation: effects on intestinal and pancreatic digestive enzyme activities.

Male Wistar rats were fed for four weeks on defined diets containing no fiber additions, 10% levels of insoluble fiber derivatives (cellulose or alfalfa), or 5% levels of viscous fiber derivatives (pectin, guar gum, or metamucil). After an overnight fast, the pancreas was assayed for protein, amylase, lipase, trypsin, and chymotrypsin. Homogenates of small intestinal mucosa were analyzed for protein, alkaline phosphatase, invertase and thymidine kinase. There were, with few exceptions, no dietary effects on the exocrine pancreatic enzymes. The specific activities of the villus marker enzymes (invertase and alkaline phosphatase) tended to be higher in the proximal (but not middle or distal) intestines of the fiber-fed groups, while total activities were the same in all groups. In contrast, the activity of the crypt marker, thymidine kinase, was highest in the distal intestinal segments, and even higher in animals given the alfalfa, guar gum or metamucil-supplemented diets.

Adaptation, Physiological↗
PubMed1985

Influence of epidermal growth factor on the maturation of the fetal mouse duodenum in organ culture.

The purpose of this work was to study the direct influence of epidermal growth factor (EGF) on the maturation of the fetal mouse duodenum in organ culture. Duodenal explants, resected at 17 days of gestation, were cultured during 48 h at 37 degrees C in Leibovitz L-15 serum-free medium alone or supplemented with EGF (100 ng/ml). Differentiation of absorptive cells was evaluated by measuring brush border hydrolytic activities. After 48 h of culture with and without EGF, villous architecture and the fine structural characteristics of the tissues are preserved. In control explants, the level of alkaline phosphatase, maltase, trehalase, and sucrase activities as well as the protein and DNA contents remain comparable to the values measured in 17-day explants at the beginning of the culture period, while lactase activity falls drastically. In explants cultured with EGF, the level of alkaline phosphatase, maltase, and trehalase activities and the protein contents significantly increase while sucrase activity and DNA contents are unchanged, and lactase activity remains under the onset level. From these results, it was concluded that EGF influences directly the maturation of some brush border enzymes in the duodenum during the fetal period.

Animals↗
PubMed1985

Permissive effect of glutamine on the differentiation of fetal mouse small intestine in organ culture.

The proximal third of the small intestine of 15-day-old mouse embryo can be cultured for 72 h at 37 degrees C. When Trowell-T8 medium is used, the integrity of the explants is maintained, but villi do not form and absorptive cells are poorly differentiated. However, when Leibovitz L-15 or RPMI-1640 medium is used, one can observe the formation of medium-sized villi, and absorptive cells in the explants are more differentiated. Since the chemical composition of T8 medium is quite different from that of the other two media, we decided to test the importance of two major differences, i.e., three amino acids and five vitamins, in order to find out which element(s) is necessary to permit the formation of intestinal villi. Subsequent testing demonstrated that the three amino acids are responsible for the effect on differentiation, and that glutamine is the only critical difference between T8 and the two other media. The results show that the addition of L-glutamine to T8 medium permits the formation of villi, the initiation of absorptive cell differentiation, an increase in DNA synthesis, and finally, an increase in the number of epithelial cells. These findings indicate that undifferentiated fetal mouse small intestine is able to express its phenotype in organ culture, even without any extrinsic regulatory influences, provided that L-glutamine is present at a sufficient level in the culture medium. The use of inhibitors indicated that L-glutamine may be essential as an energetic substrate and/or a precursor for glucosamine.

Animals↗
PubMed1984

Effect of dexamethasone on the fetal mouse small intestine in organ culture.

The formation of intestinal villi (organogenesis phase) may be studied in organ culture with a completely synthetic medium in 15-day fetal mouse duodenal explants. However, in these explants absorptive cells remained poorly differentiated with all the hormones studied except with epidermal growth factor. In order to elucidate the role of hormones and other factors on the maturation of absorptive cells (maturation phase) in the fetal rodent in organ culture, we have taken the explants after the organogenesis phase. We have studied different culture conditions and have found that 17-day mouse duodenal explants can be cultured during 48 hours with Leibovitz L-15 medium in a 95% O2-5% CO2 atmosphere provided that the explants are relatively large (5 X 2 mm). With this method, dexamethasone (Dx) has been shown to have a direct effect on the maturation of the fetal duodenal mucosa. The addition of Dx (300 ng/ml) to the completely synthetic medium 1) improves the morphology of the explants, 2) induces a significant increase in maltase activity in the tissues, and 3) reduces significantly the labeling index of the duodenal explants after 48 hours of culture. Direct action of Dx on the duodenal mucosa is shown for the first time in organ culture using a completely synthetic medium. This method will permit us to study the effects of other intrinsic and extrinsic factors on the regulation of enzymatic maturation in fetal small intestine.

Animals↗
PubMed1984

Measurement of beta-glucuronidase in effluent of perifused alveolar macrophages challenged with chemically modified chrysotile asbestos.

Chrysotile asbestos has been implicated with lung disorders, notably fibrotic lesions and cancer. In vitro, chrysotile fibers are cytotoxic to lung macrophages and stimulate the release of inflammatory mediators. Reports to the effect that chemical modifications of asbestos fibers reduce their cytotoxic and inflammatory potential initiated the present study of three fiber modifications. The cytotoxic and inflammatory effects of magnesium-leached chrysotile, POCL3-treated chrysotile, and CaO-treated chrysotile were studied in a perifused rat alveolar macrophage culture system, relative to untreated fibers. Natural Canadian chrysotile (UICC "B") caused dose-dependent cell mortality and clumping. The release of beta-glucuronidase (beta-Glu), a lysosomal enzyme, was also dose dependent. Rhodesian chrysotile (UICC "A") caused similar cytotoxic and inflammatory effects. However, magnesium-leached chrysotile was less cytotoxic (39% less) and had a lesser clumping capacity (31% less) than untreated chrysotile. Total secretion of beta-Glu elicited by magnesium-leached chrysotile was reduced by 43% from the untreated sample, but kinetic monitoring indicates that this reduction in inflammatory potential is only significant during the first 12 h of an 18-h culture period. POCl3 treatment of chrysotile fibers produced differing effects depending on the length of the fibers under study. Treating fibers with a mean length of 8 micron produced a secretion pattern similar to that produced by acid leaching. The total output for the treated sample was 44% lower than with untreated chrysotile; the difference was only significant during the first 12 h of perifusion. Cell mortality and aggregation were not reduced in any important way with POCl3 treatment of these longer fibers. When ultra-short fibers (mean length = 0.8 micron) were treated with POCl3, the total decrease in beta-Glu output was equal to 41%, and the release of enzyme was significantly lower during the whole 18-h experiment. Cell aggregation was not appreciably affected, but cell mortality was significantly lower than for untreated fibers. CaO treatment did not alter the cytotoxic (cell death and aggregation) or inflammatory (beta-Glu release) effects of chrysotile asbestos. These results suggest that chemical modifications affecting the integrity of the surface magnesium and/or the polarity of the surface charge of chrysotile can reduce to some extent the cytotoxic and inflammatory properties of this type of asbestos.

Animals↗
PubMed1984

Comparative study of some intestinal brush border membrane enzymes during perinatal development of the mouse.

Intestinal brush border membrane (bbm) fractions have been isolated from fetal and neonatal mice. The existence of discordant developmental patterns of intestinal enzymatic activity derived from total homogenate and bbm fraction was confirmed. It originates chiefly from two phenomena: (a) variations in the state of purity of brush border fractions, and (b) loss of brush border membrane enzyme activities in supernatant that increases with age. The phenomenon of solubility for glucoamylase and alkaline phosphatase is already present two days before birth.

Aging↗
PubMed1984

Plasma concentrations of clobazam and its N-desmethyl metabolite; protection against pentetrazol-induced convulsions in mice.

The anticonvulsant effects of acute administration of clobazam and its principal metabolite N-desmethylclobazam were studied in mice. Pentetrazol, given by slow intravenous infusion 1 or 2 h after the anticonvulsant dose, was used as the convulsant stimulus. Log dose response relationships for both clobazam and N-desmethylclobazam appeared linear, but there was no correlation between plasma concentrations of clobazam and protection. However, correlation between plasma concentrations of N-desmethylclobazam and protection was significant in both cases.

Animals↗
PubMed1984

Dynorphin and enkephalins in adrenal paraneurones. Opiates in the adrenal medulla.

Immunoreactive dynorphin (ir-Dyn), immunoreactive leucine-enkephalin (ir-Leu-Enk) and various other neuropeptides were measured in acid extracts of bovine adrenal medulla and isolated adrenal chromaffin cells. Their respective levels ranged as follows: Leu-Enk greater than Dyn greater than bombesin greater than vasoactive intestinal peptide (VIP) greater than neurotensin greater than substance P. Comparisons of the total catecholamine levels with the levels of Leu-Enk in both extracts gave ratios in the same order of magnitude (2600, tissue extract and 5000, cell extract). However, the catecholamine/Dyn ratio in the tissue extract (138 000) was much higher than that found in the cell extract (20 180), suggesting a possible selective degradation of Dyn in tissue extract as compared with cell extract or an induction of Dyn biosynthesis in cells which have been isolated from their natural microenvironment. Immunofluorescence staining of isolated chromaffin cell sections revealed the presence of ir-Dyn in 5 to 10% of the total cell population. To localize ir-Dyn in regard to Leu-Enk and catecholamines, adrenal chromaffin cells were separated into three populations (I, II, and III) on a stepwise bovine serum albumin (BSA) gradient. Relative high levels of ir-Dyn were measured in cell layer I (4 pmol/10(6) cells), a cell population enriched in noradrenaline. However, ir-Leu-Enk was more concentrated in cell layers II and III (5.3 and 8.3 pmol/10(6) cells), two populations enriched in adrenaline. Isolation and high pressure liquid chromatography (HPLC) analysis of adrenomedullary Dyn indicated the presence of at least five molecular forms corresponding to Dyn-(1-11), Dyn-(1-12), Dyn-(1-13), Ala-containing-Dyn-(1-13) and a nonidentified molecule eluting closely to Dyn-(1-13). These data indicate that adrenal ir-Dyn and ir-Leu-Enk have distinct cellular distributions. In addition, the identification of Dyn fragments in bovine adrenal medulla indicates that these short peptides may be considered as natural active forms of Dyn.

Adrenal Medulla↗
PubMed1983

Extracts of rat amniotic fluid contain a potent inducer of intestinal crypt formation.

The effect of acid, basic, and organic extracts from Long Evans rat amniotic fluid (RAF) and from Swiss ICR mouse amniotic fluid (MAF) was studied on 15-day fetal mouse duodenal mucosa in organ culture. Amniotic fluids (20 ml) were lyophilized and extracted 1) with CHCl3:MeOH and the organic phase was evaporated; then 2), the residue was acidified with a solution of 0.1 N HCl in 10% acetic acid and the liquid phase was lyophilized; finally 3), 0.01 M NH4OH was added to the residue and the liquid phase was lyophilized. The product of each extraction was added to 20 ml of Trowell T8 medium. Acid and basic extracts of RAF and MAF have no effect on the formation of duodenal villi and crypts after 48 hours of culture. With the organic extract of MAF, small villi are present after 48 hours of culture and absorptive cells are poorly differentiated. With the organic extract of RAF, well-developed villi have differentiated after 48 hours of culture; moreover, crypts are present at the same stage and Paneth cells are identified within these crypts. During the 8-10 hour period, the explants cultured with the Trowell T8 medium supplemented with RAF or MAF organic extracts show a 35% increase in 3H-thymidine incorporation over the controls cultured with Trowell T8 medium alone. These results indicate that organic extracts from MAF and RAF are able to promote villus formation in undifferentiated explants from 15-day fetal mouse duodenum in organ culture. Furthermore, RAF organic extract contains a factor that can induce the formation of duodenal crypts and the differentiation of Paneth cells in culture at least 2 days before their normal appearance.

Amniotic Fluid↗
PubMed1983

Development of peroxisomes in amphibians. III. Study on liver, kidney, and intestine during thyroxine-induced metamorphosis.

This investigation was undertaken to study the ontogeny of hepatic, renal, and intestinal peroxisomes and/or microperoxisomes during thyroxine-induced anuran metamorphosis. Catalase activity was localized cytochemically after incubation in DAB medium, and studied biochemically by a spectrophotometric method. Our morphological and biochemical investigations suggest the formation of a new population of peroxisomes during the hormonal treatment. This is obvious especially for microperoxisomes of the intestinal epithelium since the larval tissue is completely replaced by a new layer during thyroxine-induced metamorphosis. For the peroxisomes of hepatocytes and kidney proximal tubule cells, our assumption is based on the following observations: 1) The number of peroxisomes increases in liver and kidney during thyroxine treatment; 2) this proliferation is accompanied by an enlargement of renal peroxisomes; and 3) 16 days after the beginning of the hormonal treatment, 5.4- and 2.4-fold increases are found for the specific activities of hepatic and renal catalase, respectively. A temporal coordination exists between the structure and the metabolism of peroxisomes and mitochondria during thyroxine-induced metamorphosis.

Animals↗
PubMed1983

The hemolytic activity of chrysotile asbestos fibers: a freeze-fracture study.

Short asbestos fibers isolated by a sedimentation procedure have a strong hemolytic activity. In the presence of ferritin particles, hemolysis by chrysotile fibers is inhibited at least during the first 10 min. Freeze-fracture studies show that after 20 sec or 2 min of contact between the fibers and the RBC membrane, the intramembranous particles remain randomly distributed over the whole surface of the P-face. On the E-face of the asbestos-treated red blood cell membranes, the number of intramembranous particles is significantly reduced. With the transmission electron microscopy, it is not possible to resolve the trilaminar structure of the ghost membrane around the deeply buried asbestos fibers. It is postulated that the membrane defects brought about by asbestos are caused by the adsorption of one membrane constituent, possibly phospholipids, on the chrysotile fibers.

Animals↗
PubMed1983

A comparative study on the hemolytic action of short asbestos fibers on human, rat, and sheep erythrocytes.

The hemolytic activity of short asbestos fibers isolated by a sedimentation procedure was studied using human (HRBC), rat (RRBC), and sheep (SRBC) red blood cells. The initial velocity (Vi) of hemolysis is proportional to the concentration of fibers with HRBC and RRBC, but not with SRBC. Initial velocity (Vi) is 14.30 for HRBC, 5.75 for RRBC, and 3.60 for SRBC at a concentration of 1,000 micrograms of fibers/ml. Maximum velocity (Vm) is reached at 400 micrograms/ml with HRBC and its value is 16.7. With RRBC and SRBC, Vm is reached at 600 micrograms/ml and its value is 10 and 3.6, respectively. The 50% hemolytic concentration (HC50) at 60 min of incubation is 75 micrograms/ml for HRBC, 240 micrograms/ml for RRBC, and 260 micrograms/ml for SRBC. It appears that the sensitivity against the short asbestos fibers of the three types of RBC used is in the following order: HRBC greater than RRBC greater than SRBC.

Animals↗
PubMed1983

An adherent cell perifusion technique to study the overall and sequential response of rat alveolar macrophages to toxic substances.

Essentially pure (97%) alveolar macrophages were isolated by bronchoalveolar lavage of rats with warm (37 degrees C) PBS solution. These cells were allowed to adhere to the inside walls of open-ended glass cylinders which were closed off at each end by three-way stopcocks. The adhering cells were perifused with RPMI-1640 medium supplemented with 5% fetal bovine serum for 18 hr at the rate of 1 mL/hr, and the effluent medium was collected automatically in 2-mL aliquots. Cell recoveries and viabilities did not differ from those found for Petri cultures treated similarly, indicating that the perifusion method under study offered an adequate milieu for short-term primary cultures. The alveolar macrophages in culture were subjected to the presence of particulate (chrysotile asbestos) and soluble (phorbol myristate) toxicants, and their response was monitored in the effluent medium by measuring the release of prostaglandins (PGE) by radioimmunoassay. A significant increase in the sequential release of PGE was observed in the presence of asbestos (100 micrograms/mL) or phorbol myristate (200 ng/mL). Treatment of the cells with indomethacin (20 microM) completely abolished the release of PGE stimulated with phorbol myristate. A cumulative response to the toxicants was also observed when cells were harvested manually from the chambers: asbestos caused a 2-fold increase in cell mortality relative to control, while phorbol myristate brought about a 3-fold increase in the number of dead cells. This effect was not prevented by the presence of indomethacin. Cell aggregation was also observed when cells were perifused in the presence of phorbol myristate, whether indomethacin was present or absent. Our results indicate that the cell perifusion system combines the advantages of conventional adherent cell cultures (viability, aggregation) with those of perifusion techniques (sequential metabolism studies).

Animals↗
PubMed1982

Development of peroxisomes in amphibians. II. Cytochemical and biochemical studies on the liver, kidney, and pancreas.

The ontogeny of catalase-containing organelles was studied by cytochemical and biochemical methods in the liver, kidney, and pancreas during the development of Rana catesbeiana. The biochemical differentiation of peroxisome in the liver and kidney was compared to that of Xenopus laevis. Catalase activity was localized after incubation in DAB medium and studied biochemically by a spectrophotometric method. In Rana Catesbeiana the number of catalase-positive organelles per cell section is low in all three organs during premetamorphosis; their number increases substantially in the liver and kidney of froglets, while it remains almost stable in the pancreas. No further increase is observed in the adult. Biochemically, the liver, kidney, and pancreas of tadpoles exhibit, respectively, 12,22 and 63% of the catalase activity found in the adult tissues. After metamorphosis an important increase of catalase activity is particularly noted in liver and kidney, the activity being, respectively, 43 and 77% of that of adult bullfrogs. On the other hand, no change in catalase activity in the liver and kidney is noted during the entire development of Xenopus laevis. The present study illustrates the very different developmental pattern of catalase activity observed during the development of two anuran amphibians. The different development pattern of the same enzyme within the small intestine, liver, kidney, and pancreas in Rana catesbeiana is also stressed.

Aging↗