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Biomedical subjects

M Bergeron

Publications and source records attributed to M Bergeron.

At least 91 records · Page 5Linked to original sources
PubMed1980

Existence of an endogenous inhibitor of DNA synthesis in rabbit small intestine specifically effective on cell proliferation in adult mouse intestine.

Aqueous extracts from rabbit organs were prepared by homogenization and centrifugation at 105,000 g. After precipitation with ammonium sulphate, the 0-50 fraction was separated by ultrafiltration through Amicon XM 100 and XM 300 membranes yielding two filtrate fractions (U1 and U2) and one retentate fraction (U3). Only U1 and U3 inhibited thymidine incorporation into DNA. After a single injection of U1 from rabbit small intestine, the uptake of tritiated thymidine was decreased in mouse jejunal and colonic DNA. This effect, totally reversible after 7 hr, was found in neither the kidney nor the testis. The U1 fractions of colon and non-digestive organs (kidney, testis) were found not to exert a significant inhibition on thymidine incorporation into intestinal DNA in vivo. The U3 fraction from rabbit small intestine also decreased the uptake of tritiated thymidine in mouse jejunal and colonic DNA in vivo. However, this inhibition was irreversible and not tissue-specific. Slowing of cell migration was also noticed in the jejunum of mice injected with U1 or U3, as ascertained radioautographically by determining the position of the leading edge of the labelled cells in U1- or U3-injected mice compared with controls. A decrease of mitotic activity in U1- and U3-injected mice was recorded 8.5 hr after a single injection of small intestinal fractions. Our results suggest that U1 and U3 from rabbit small intestine contain one or more substances which may act on the G1-S transition of the cell cycle in the mouse intestine. However, only the effect of U1 is reversible and tissue specific. Our data suggest the existence of a factor, having a low molecular weight, which regulates intestinal cell proliferation.

Animals↗
PubMed1979

Nonparticipation of extracellular glutathione in renal transport of dibasic amino acids.

Microinjections of L-[14C]arginine (2.9 mM) and L-[14C]ornithine (3.4 mM) were made into renal proximal tubules of rats in the presence of methionine sulfoximine (MSO) (10, 20 mM), ATP (10 mM), and MgCl2 (20 mM) together. Absorption of both labelled amino acids dropped, respectively, by 31.1 and 49.1% compared with control microinjections. The MSO alone or ATP plus MgCl2 had no effect. These data suggest that the inhibition by MSO plus ATP plus MgCl2 is not due to direct competition between MSO and dibasic amino acids but rather to suppression of the renewal of intracellular glutathione. Such an effect is discussed in comparison with cycloleucine inhibition of dibasic amino acid transport. Addition of exogenous glutathione to microinjectates die not reverse either type of inhibition. This study shows that while intracellular glutathione may affect amino acid transport, extracellular glutathione has no effect.

Absorption↗
PubMed1978

Experimental cystinuria: the cycloleucine model. II. Amino acid efflux from intestinal and renal tissues.

Loading and unloading experiments using intestinal sacs and renal cortex slices were undertaken to ascertain the role of amino acid efflux in cycloleucine-induced amino-aciduria. The presence of cycloleucine, lysine, or valine on the luminal or antiluminal side of the intestine caused an increased leakage of [14C] cycloleucine, [14C] lysine, and [35S] cystine from the tissue. Similar results were obtained when using kidney cortex slices, except for cystine efflux. The latter phenomenon was inhibited by cycloleucine and lysine. Data, also obtained with renal cortex slices, suggest that cystine and cysteine are recognized by different transport sites although one (the oxidized form) may be typically extracellular and the other (the reduced form), intracellular. A comparison of these data with previous works done in our laboratory shows that cycloleucine affects efflux less than influx and further suggests that in rats given cycloleucine, renal transport is impaired only at the brush border level for cystine and at both luminal and antiluminal membranes for dibasic amino acids.

Amino Acids↗
PubMed1977

Specific inhibition of cell proliferation in the mouse intestine by an aqueous extract of rabbit small intestine.

An aqueous extract was prepared from the mucosa of rabbit small intestine by homogenization and centrifugation at 105,000 g. After precipitation with ammonium sulfate, the 0-50 fraction (F1) and the supernatant (F2) were collected, dialysed against a phosphate buffer and tested on rats in vitro and mice in vivo. The F1 fraction was found to inhibit thymidine incorporation into rat intestinal DNA in vitro, but this effect was not found to be tissue specific (liver, kidney). Two hours after a single injection of F1 (10 mg protein content), the uptake of tritiated thymidine was decreased in jejunal and colonic DNA in mice. This effect was maximal between 2 and 4 hr and totally reversible after 7 hr; this effect was found in neither the kidney nor the testis. A slowing of cellular migration was also noticed in the jejunum and the colon. Conversely, the F2 fraction did not inhibit the synthesis of jejunal and colonic DNA either in vitro or in vivo. Our results suggest that the F1 fraction of the aqueous extract of rabbit small intestine contains one or more substances which may act either on intestinal DNA synthesis or on the GI--S transition of the cellular cycle in the mouse intestine. This reversible and specific intestinal action appears to inhibit cell proliferation and presents several of the characteristics defining a chalone.

Animals↗
PubMed1977

Morphologic changes during incubation of renal slices.

The progression of ultrastructural changes was studied during various conditions of incubation of rat and mice renal cortex slices. The kidneys were sliced with a Stadie-Riggs microtome and incubated in various media (tris(hydroxymethyl) aminomethane (Tris), Tris-proline, and Hanks), in different oxygenation conditions (O2-CO2, 6 liters per minute; N2, 0.5 liter per minute), at different temperatures (37 degrees C, 23 degrees C.) and different time intervals (0 to 120 minutes). The most conspicious changes appear to involve plasma membranes and mitochondria. Early changes (0 to 30 minutes) are mainly confined to mitochondria cristae and matrix; there is also light swelling of the endoplasmic reticulum. After 30 minutes of incubation, the majority of mitochondria have a condensed form: dense matrix and slight dilation of the cristae. These modifications are more accentuated at 75 minutes and many mitochondria are swollen and contain dense material. The modification of the membrane takes place at 30 minutes by vesiculation and/or a diffuse dilation of brush border and is followed by myelinization. The antiluminal membrane appears less sensitive but the same modification pattern appears after 75 minutes. These changes appear more slowly at 23 degrees C. than at 37 degrees C. Kinetic studies were also carried out confirming findings of various authors; cellular uptake and accumulation of 14C-glycine still take place after 2 hours of incubation. The kidney cortex slicing technique does not seem to be suitable for the study of absorption at the luminal membrane. Furthermore, our observations suggest that the generally accepted ultrastructure of some organelles does not correspond to their appearance in the noramlly functioning state in vivo.

Animals↗
PubMed1976

A method for the study of the inhibition of DNA synthesis by rabbit tissue extracts.

This paper describes a method to measure DNA synthesis in the jejunum. Everted rings of rat jejunum were incubated in the presence of (3H) thymidine. The specific activity of jejunal DNA was assayed at the end of incubation. This method was found to be valid when (1) incubation time was 30 min, (2) (3H) thymidine concentration was 90 ng/ml, and (3) paired flasks containing four, respectively, contiguous rings were compared. This method was used to investigate the existence of an intestinal chalone. An aqueous extract (S-105)of rabbit small intestine mucosa was prepared and tested for DNA synthesis inhibition in jejunum. A significant inhibition was noted, which was an hyperbolic function of the quantity of extract present in the media. The study of S-105 inhibition on other organs (kidney, liver, colon) failed to demonstrate organ specificity. However, aqueous extracts from intestinal organs were found to exert a greater inhibition than aqueous extracts form other organs. It is suggested that S-105 contains other nonspecific inhibitory fractions; our data prove the necessity of an extensive purification to demonstrate the existence of a specific chalone that regulates intestinal cell proliferation.

Animals↗
PubMed1976

Membrane permeability as a cause of transport defects in experimental Fanconi syndrome. A new hypothesis.

The injection of sodium maleate (200-400 mg/kg) into rats produces aminoaciduria along with glycosuria and phosphaturia, resembling the Fanconi syndrome. This experimental model was studied by means of microinjections into proximal convoluted tubules of the kidney, stop-flow diuresis, and microperfusion of single nephrons. Our results show that, in maleate-treated rats, competition between amino acids or related structures (L-proline, L-OH-proline, and glycine) possesses the same characteristics, and net influx of amino acids appear normal at the proximal nephron. Data obtained by classical stop-flow techniques and single nephron microperfusions also indicate a normal entry of labeled amino acids (L-lysine, glycine, L-valine, L-proline, L-cystine), and 3-0-methyl-D-[3H]glucose and [32P]phosphate from the luminal side of the proximal tubule cell. However, the efflux of molecules from the cell appears enhanced throughout the proximal and distal tubule; molecules that exit at this site are excreted directly into the urine. Our results suggest that the phosphaturia, aminoaciduria, and glycosuria of the experimental Fanconi syndrome can be explained by a modification of the cell membrane permeability (increased efflux) at distal sites of the nephron rather than by a modification of the membrane transport (decreased influx) at the proximal sites, as is currently accepted. Our data also stress the importance of efflux phenomena in membrane transport.

Amino Acids↗
PubMed1976

[Spatial morphology of the mitochondria of the proximal and distal tubules of the kidney].

A new histological technique of block staining based on the use of a double lead and copper citrate is described in order to observe thick sections (0.5-1.5 micron) with a transmission electron microscope. With this technique, a network of mitochondrial with many morphological communications was seen in the epithelial cells of the proximal and distal convoluted tubules of the rat nephron. A new schematic view of the proximal and distal tubular cell is presented to illustrate the communications of the chondriome, which could become more or less accentuated following the functional status of the cell.

Animals↗
PubMed1975

Experimental cystinuria: the cycloleucine model. I. Amino acid interactions in renal and intestinal epithelia.

The injection of cycloleucine (1-aminocyclopentanecarboxylic acid (ACPC) into rats produces a hyperexcretion of dibasic amino acids and cystine, an aberration resembling cystinuria. This may constitute a model of experimental cystinuria, and the transport of amino acids involved in this disease was studied with the techniques of everted intestinal sacs (in vitro) and microinjections into renal tubules (in vivo). In verted sacs from normal rats, there was a decrease in transfer and in accumulation of L-cystine (0.03 mM) and L-valine (0.065 mM) when ACPC was on the mucosal (luminal) side. Dibasic amino acids such as L-arginine and L-lysine caused a similar inhibition of the transport of L-cystine. However, when ACPC was on the serosal (antiluminal) side, a lesser effect was noted while arginine and lysine had no effect. Intestinal sacs from treated rats (ACPC, 300 mg/kg X 3 days) transferred and accumulated as much L-cystine as those from control rats. The interaction between cycloleucine and L-cystine was competitive at the luminal and non-competitive at the antiluminal side of the intestine. Cycloleucine inhibited L-lysine transport in a non-competitive fashion at either side of the intestine. L-Lysine also interacted in a non-competitive fashion with L-cystine transport at the luminal membrane. In proximal convoluted tubules, the presence of L-arginine or ACPC caused a decrease in the transport of L-cystine and L-lysine. L-Valine exerted no effect. Furthermore, L-lysine and ACPC did not impair the reabsorption of L-valine significantly. These results suggest a functional heterogeneity between luminal and antiluminal membranes of renal and intestinal epitehlia and the existence, at both membranes, of different transport sites for cystine and dibasic amino acids.

Amino Acids↗