Biomedical subjects

D Ménard

Publications and source records attributed to D Ménard.

At least 55 records · Page 3Linked to original sources

PubMed1996

Rapid estimation of Escherichia coli in live marine bivalve shellfish using automated conductance measurement.

Conductance measurement for quantitative estimations of Escherichia coli in live bivalve shellfish was evaluated as an alternative to the conventional most probable number (MPN) method used in France. The sensitivity of the two techniques was comparable. A single regression line (r = -0.968, P < 10(-6)) between log10 MPN and detection time (DT) was used to estimate E. coli concentrations for all shellfish examined. Estimation accuracy was +/- 0.92 log unit. Repeatability was better for DT than the log10 of MPN estimations (average coefficients of variation 2.7 and 9.3%, respectively). The conductance signal was attributable to E. coli in 96% of cases, and only 0.7% of E. coli cultures failed to exhibit a signal within 20 h. The conductance method reduces analysis handling time and is much easier to use than the MPN method. Moreover, results can be obtained within 5-9 h compared to 3 d for the MPN method.

Animals↗

PubMed1996

Lipid processing and lipoprotein synthesis by the developing human fetal colon.

Despite significant progress in the elucidation of the ontogeny of gastrointestinal function, little attention has been given to colonic lipid processing during development. The major purpose of this study was to explore the intracellular phase of fat absorption, lipid synthesis, and secretion in the human fetal colon compared with the jejunum originating from the same fetuses. The synthesis of lipids and major apolipoproteins was examined using cultured fetal colonic explants incubated with [14C]oleic acid and [36S]methionine, respectively. Fetal colonic explants demonstrated substantial ability to incorporate [14C]oleic acid (dpm/mg protein) into phospholipids (48,743 +/- 4,783), triglycerides (25,687 +/- 2,469), and cholesteryl esters (6,751 +/- 1,227). The total amount of radiolabeled lipids was much higher within the tissue (87,472 +/- 9,142) than in the medium (51,916 +/- 4,970), indicating a limited capacity of the fetal colon to export newly synthesized lipids. The limited colonic lipid secretory process was even more evident when compared with homologous fetal jejunal de novo synthesized lipids in tissue (133,975 +/- 13,836) and medium (279,858 +/- 1,610), respectively. Similar to the jejunum, the colon was able to elaborate all the phospholipid classes, with phosphatidylcholine accounting for > 70% of tissue phospholipids. However, their individual levels were present in lesser amounts in the colon (P < 0.001). Colonic explants elaborated most of the major lipoprotein classes but were less efficient than jejunal explants in exporting chylomicrons (33-fold), very low density lipoprotein (1.5-fold), and high-density lipoprotein (9-fold) into the medium. Apolipoprotein (apo) B synthesis and apo B mRNA editing were comparable in colonic and jejunal explants; thus they are not responsible for the defective lipoprotein secretion in the fetal large bowel. These results establish for the first time te capability of the human fetal colon to form, but not to efficiently transport, lipids, lipoproteins, and apoproteins.

Apolipoproteins B↗

PubMed1996

Peroxisomes and peroxisomal enzymes in the human fetal small intestine.

The appearance and development of peroxisomes and the expression of their enzymes in the human fetal intestine have been investigated between 11 and 22 weeks of gestation. In the youngest samples (11-16 weeks of age), cytochemistry at the ultrastructural level revealed the presence of rare, mostly circular peroxisomes. From 16 weeks of gestation onwards, an increase was noted in the number of peroxisomes. Two peroxisomal types were distinguished: round to oval forms and elongated and/or tailed organelles. Biochemical assays revealed that total and specific intestinal catalase activities increased gradually between 11 and 20 weeks of gestation. The activity of fatty acylCoA oxidase, the first enzyme of the peroxisomal beta-oxidation system, was detectable as early as 11 weeks of gestation. Thereafter, total and specific activities of the enzyme increased steadily. Activities of other peroxisomal oxidases (D-amino acid oxidase, L-alpha-hydroxyacid oxidase) appeared more slowly in the fetal intestine during the period studied. This investigation establishes the presence and the morphological changes that occur in intestinal peroxisomes during human fetal development as well as the developmental patterns of associated enzymes.

Acyl-CoA Dehydrogenase↗

PubMed1996

Developmental expression of calcitriol receptors, 9-kilodalton calcium-binding protein, and calcidiol 24-hydroxylase in human intestine.

Human intestinal mucosa consists of highly active epithelial cells in continual renewal and differentiation processes located at different portions of the villi. The crypt contains abundant replicating cells which, upon reaching the villus tip, acquire their fully differentiated state. Besides its well recognized role in bone cell homeostasis, calcitriol has been attributed a role in cellular differentiation and proliferation in normal leukocytes and myeloid leukemia cells. We have previously documented the presence and the distribution of specific calcitriol receptors in the cells of the small and large intestine from 13-20-wk-old human fetuses and that calcitriol was able to promote human intestinal epithelium proliferation or differentiation, in organ culture, depending upon fetal age. We now show that, whereas transcripts for calcitriol receptors are abundant from duodenum to colon, those for the 9-kD calcium-binding protein are present mainly in the duodenum and the jejunum and to a lesser extent in the ileum and the colon. Transcripts for 25-hydroxycholecalciferol-24-hydroxylase could not be detected in any of the intestine segments despite a prolonged exposition of the gels. Immunofluorescence staining for the 9-kD calcium-binding protein was exclusively observed in the epithelial cells of the small intestine and colon, the subepithelial layers being always negative. The 9-kD calcium-binding protein distribution along the crypt-villus axis appeared as a gradient, increasing from the developing crypt to the tip of the villus in the duodenum, jejunum, and ileum. Based on the present observations and on the fact that calcitriol promotes human fetal proliferation and differentiation, the presence of transcripts for calcitriol receptors and 9-kD calcium-binding protein in the intestinal cell opens interesting possibilities as of their role in the in utero human gut development and the control of colorectal cancers.

Calcium-Binding Proteins↗

PubMed1995

Morphological studies of the developing human esophageal epithelium.

This article focusses on the structural development of human esophageal ciliated epithelium. A combination of transmission electron microscopic (TEM), scanning electron microscopic (SEM), radioautographic, and light microscopic (LM) analyses were carried out using intact fetal tissues between 8 and 20 weeks of gestation as well as cultured esophageal explants. Up to the age of 10 weeks, the stratified esophageal epithelium consisted of two longitudinal primary folds. The surface cells were undifferentiated and contained large glycogen aggregates. Between 11 and 16 weeks, the primary folds (now up to four) had developed secondary folds. The thickness of the epithelium drastically increased (123%) in concomittance with a differentiation of surface columnar ciliated cells. These highly specialized surface cells exhibited junctional complexes and well-developed organelles with numerous microvilli interspersed among the cilia. Transverse sections revealed the internal structure of the cilia with a consistent pattern of nine doublet microtubules surrounding a central pair of single microtubules. Freeze-fracture studies illustrated the presence of a ciliary necklace composed of 6 ring-like rows of intramembranous particles. They also revealed the structure of ciliary cell tight junctions consisting of up to nine anastomosing strands (P-face) or complementary grooves (E-face). Ultrastructural studies (LM, TEM, SEM) of the esophageal squamous epithelium obtained after 15 days of culture showed that the newly formed epithelium was similar to adult human epithelium. Finally LM and SEM observations established that the esophagogastric junction was not yet well delineated, consisting of a transitional area composed of a mixture of esophageal ciliated cells and gastric columnar mucous cells.

Autoradiography↗

PubMed1995

Ontogeny of human gastric lipase and pepsin activities.

BACKGROUND/AIMS: The developmental profile of human gastric lipase activity as well as the secretory capacity of the immature gastric mucosa are still unknown. The aims of this study were to establish tissue activity levels for lipase and pepsin in the various anatomical regions of the developing stomach and to assess whether lipase is secreted by the fetal gastric mucosa. METHODS: Lipase and pepsin activities were assayed in 49 specimens of different gestational ages. Gastric explants were cultured in chemically defined medium for up to 5 days, and enzymic activities were measured in tissues and in the culture media. RESULTS: Lipolytic activity was present in gastric tissues at 10-13 weeks and steadily increased for up to 20 weeks, whereas pepsin activity did not vary significantly over the periods of study. There was a clear decreasing gradient of lipase activity; the highest activity was in the fundic area, and the lowest activity was in the antrum. Quantitative pepsin activity did not vary over the gastric regions. During culture, total lipolytic and pepsin activity increased 3.8-fold, and both enzymes were secreted into the culture medium. CONCLUSIONS: Gastric lipase appears as early as 10-13 weeks. Adult distribution of the enzyme became established by 16 weeks' gestation. The secretion of lipase into the organ culture suggests that the gastric mucosa is the main source of lipolytic activity in gastric aspirates of premature infants.

Female↗

PubMed1995

Structure-activity analysis of the motor effects of neuropeptide Y.

The purpose of the present study was to examine structure-activity relationships for three known motor effects of neuropeptide Y (NPY): decreased spontaneous activity, enhancement of muscle tone, and catalepsy. Various NPY fragments and structural analogues were synthesized and administered intracerebroventricularly in several doses (2.5-160 micrograms); their effects on these three motor variables were evaluated and compared. Globally, results indicate that the C-terminal portion of the peptide is responsible for the three motor effects of NPY. However, the distributions of potencies of the various fragments and analogues for each effect were clearly different, suggesting that the putative receptors mediating each motor effect are pharmacologically different. The findings of the present work are discussed in relation to those obtained in previous structure-activity studies.

Animals↗

PubMed1995

Effects of calcitriol on proliferation and differentiation of human fetal jejunum.

Several lines of evidence suggest a role for calcitriol in the regulatory mechanisms of intestinal development. Using organ culture as a model, we have verified whether this hormone influenced the cellular proliferation and differentiation processes of the developing human jejunum. We show that calcitriol supports a proliferative process in the fetal human jejunum at 11 weeks of gestation and a differentiating activity in samples obtained between 16 and 20 weeks. The present data therefore suggest that calcitriol has a biphasic effect on the development of the human intestinal epithelium and warrants caution in extrapolating to human, data observed in developing rodents and human carcinoma cell lines.

Calcitriol↗

PubMed1995

ET-1 stimulates Ca2+ currents in cardiac cells.

Using the whole-cell voltage-clamp technique, endothelin (ET-1) was found to stimulate T- and L-type Ca2+ currents in a dose-dependent manner in both human and chick ventricular single cells. However, ET-1 had no effect on both the fast sodium current and the delayed outward K+ current in these cells. The effect of ET-1 on both Ca2+ currents was blocked by the ET(A) receptor antagonist BQ123. Treatment of single ventricular cells with pertussis toxin (PTX) prevented stimulation of T- and L-type calcium currents by ET-1. These results suggest that there are functional ET(A) receptors in both human and chick ventricular cells. The stimulation of both types of Ca2+ currents appears to be mediated by a PTX-sensitive G-protein.

Animals↗

PubMed1994

Apolipoprotein synthesis in human fetal intestine: regulation by epidermal growth factor.

In this investigation, human fetal intestine (17-20 wk) was used to study the synthesis of apolipoproteins (apo) A-I and B and its modulation by epidermal growth factor. Cultured jejunal explants were incubated with [3%S]-methionine, homogenized, immunoprecipitated and subjected to gel analysis. Radioactivity was detected mostly in apo A-I and, to a lesser extent, in both apo B-48 and apo B-100. However, apo B-48 was always the predominant form. The addition of EGF (100 ng/ml) resulted in a simultaneous decrease in apo B-100 synthesis and increase in apo B-48 production without a marked effect on apo A-I. Moreover, the incubation of jejunal explants with [14C] oleic acid documented the ability of fetal intestine to produce chylomicrons, VLDL, LDL and HDL. Therefore, the human fetal intestine has an efficient lipoprotein-lipid transport system and EGF is able to modulate levels of both apo B species as well as lipoprotein fractions.

Abortion, Legal↗

PubMed1994

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)

Animals↗

PubMed1994

Analytical procedure for use of conductance measurement to estimate Escherichia coli in shellfish.

Assays were performed with a Malthus AT Microbiological Analyzer to define an analytical procedure to estimate Escherichia coli counts in live bivalve shellfish by conductance measurement. The growth conditions used (Malthus Coliform Broth at 44 degrees C) were selective for E. coli, and interference was noted only when Klebsiella pneumoniae were at least 100 times as numerous as E. coli. Different sample preparation procedures and seeding conditions were tested to obtain good quality conductance curves. The best results were observed when: (a) meat and shell liquor were diluted 1:3 with tryptone salt water and homogenized in a Waring blender for 1 min at 15,000 rev min-1; and (b) the inoculum was taken from the liquid phase of the homogenate 20 min after blending and mixed immediately with the culture medium. Detection parameter threshold values were adjusted (first difference 1.5 microS for the baseline and 3.5 microS for detection, second difference 0.2 microS) to improve detection time reliability. The repeatability of conductance measurements was very good (S.D. as % response mean ranged from 1.9 to 3.3) with the protocol used.

Animals↗

PubMed1994

Development of human intestinal and gastric enzymes.

In humans as opposed to rodents development of the gastrointestinal tract is much less coordinated with functional changes occurring at different times during the fetal period. This article reviews developmental patterns of intestinal brush border enzymes, lysosomal enzymes, peroxisomal enzymes and de novo synthesis of intestinal lipoproteins. It also describes the developmental patterns of gastric lipase and pepsin during early fetal life. Data are presented on the most recent observations related to the regulatory mechanisms in the development of human intestinal brush border hydrolases. A clearer understanding of the ontogeny and of the regulatory mechanism of the functional development of the gastrointestinal tract will enable researchers and clinicians to improve nutritional support in a fashion appropriate for the digestive and metabolic capabilities of an infant at any developmental stage.

Humans↗

PubMed1993

Atrial natriuretic factor blocks the high-threshold Ca2+ current and increases K+ current in fetal single ventricular cells.

The effect of atriopeptin III (ANF) was studied on K+, Ca2+ and Na+ currents of single heart cells of 10-day-old chick embryos and 17- to 20-week old human fetuses. ANF III (2 x 10(-9) M) greatly decreased the basal and cAMP prestimulated high-threshold (IL) Ca2+ current without affecting the low-threshold Ca2+ current (IT) or the TTX-sensitive fast inward Na+ current. ANF III was also found to increase the delayed outward K+ currents (IK) in a dose-dependent fashion (10(-10) to 10(-7) M). The effects of ANF III on IK and IL were reversible upon washout of this hormone. Increasing intracellular guanosine 3',5'-cyclic monophosphate (cGMP) blocked IL but had no effect on IK. These results suggested that ANF regulated one type of Ca2+ current and the delayed outward K+ current in single heart cells. The effects of ANF on IL (but not on IK) could be due in part to the increased [cGMP]i levels or to an unknown signal transduction that is stimulated by this hormone.

Animals↗

PubMed1993

Maturation of human fetal stomach in organ culture.

BACKGROUND: This investigation was undertaken to establish a serum-free organ culture technique allowing for the morphological and physiological maintenance of human fetal stomach in vitro. METHODS: Explants from gastric corpuses (12-17 weeks of gestation) were cultured in serum-free medium for periods of up to 15 days. RESULTS: After 15 days of culture, surface mucous cells were more mature, gastric glands were numerous and well developed, and all epithelial cell types were morphologically very well preserved. Morphometric measurements of the glands revealed an accelerated development in culture compared with that found in utero. Even though the incorporation of [3H]thymidine into total DNA decreased, the labeling indices determined by radioautography confirmed that epithelial cell proliferation was maintained especially in the pit/neck portion and at the base of the glandular compartments. A significant increase in total glycoprotein synthesis, as evaluated by the incorporation of [3H]glucosamine, was observed and correlated with the differentiation of the mucous cells. CONCLUSIONS: This investigation establishes for the first time that human gastric mucosa can be maintained up to 15 days in organ culture and that maturation of the gastric mucosa can be reproduced in chemically defined media.

Cell Differentiation↗

PubMed1993

Stimulatory effects of insulin on DNA synthesis in suckling mouse colon.

The influence of insulin on the postnatal development of DNA synthesis and epithelial and muscular cell proliferation has been studied in suckling mice. Daily administration of insulin (12.5 mU/g body weight) during 3 days to 8-day-old mice induced a significant increase of the incorporation of [3H]-thymidine into DNA in the small intestine and the proximal and distal halves of the colon. The esophagus and the glandular portion of the stomach did not respond. A detailed analysis of the proximal and distal colon between 4 and 30 days revealed a decrease of [3H]-thymidine incorporation into total DNA during this period. However, the establishment of the labeling indices in specific compartments such as the epithelium and the muscularis externa revealed that the epithelial cellular proliferation increased around weaning period in both segments while a drastic reduction of cellular proliferation occurred in the muscle layer. A premature rise of the circulating insulin level induced a significant increase of the epithelial labeling indices in both colonic segments but remained without effects on the muscular layer. These results suggest an important role of insulin in the modulation of the ontogenic changes in epithelial cell proliferation of the mouse colon.

Animals↗

PubMed1992

Insulin decreases chylomicron production in human fetal small intestine.

The objective of this study was to examine the effect of insulin on lipoprotein synthesis and secretion in human fetal intestine. Jejunal explants were cultured with [14C]oleic acid in Leibovitz medium for 42 h. Although the addition of insulin (30 U) did not alter the incorporation of [14C]oleic acid into triglycerides, phospholipids and cholesteryl esters in the tissue, it significantly decreased (P < 0.05) the level of triglycerides (20%) in the medium. Among the three lipoprotein classes (chylomicron, VLDL, and HDL) isolated by ultracentrifugation, the chylomicron level was found significantly (P < 0.05) diminished in the medium (29%). Neither the lipid chemical composition of CM or that of VLDL, LDL and HDL was affected by the presence of insulin. These results suggest that chylomicron synthesis is modulated by insulin, whereas lipoprotein distribution and lipid composition are not regulated by this hormone.

Chylomicrons↗

PubMed1992

The expression of lactase enzymatic activity and mRNA in human fetal jejunum. Effect of organ culture and of treatment with hydrocortisone.

Very sensitive procedures were developed for the parallel determination of intestinal lactase (LPH) activity and the cognate mRNA. Between 14 and 20 weeks of gestation, lactase activity is low and varies only slightly; at 37 weeks, a relatively high level of activity is observed. The amounts of LPH mRNA correlates with the enzymatic activity (r = 0.64). Culture of fetal jejunal explants for 5 days induces by itself a 2-fold increase in LPH mRNA, without any significant change in lactase enzymatic activity. This increase may reflect the loss of a negative transcriptional regulation operative in vivo, and suggests an additional post-transcriptional regulatory component. The addition of hydrocortisone (50 ng/ml) during culture induces a doubling of lactase activity without variation in LHP mRNA, indicating a post-transcriptional modulation by hydrocortisone. The intestinal lysosomal acid beta-galactosidase activity was shown to be unaffected by hydrocortisone treatment. This observation clearly illustrates that the two intestinal beta-galactosidases are regulated differently. Our results suggests a complex developmental regulation of human intestinal lactase and that the perinatal increase in lactase activity could be modulated at a post-transcriptional level by hydrocortisone.

Gene Expression Regulation, Enzymologic↗