S. Mitjavila

Sensitivity of Na+-coupled d-glucose uptake, Mg2+-ATPase and sucrase to perturbations of the fluidity of brush-border membrane vesicles induced by n-aliphatic alcohols

The aim of our work is to show the importance of the role of hydrophobic bonds in maintaining Mg2+-ATPase or sucrase activity and Na+-coupled D-glucose uptake normal for the brush border of rat enterocytes. The activity of the two enzymes and the D-glucose uptake were therefore measured under the action of n-aliphatic alcohols and related to the fluidity determined by ESR. Three concentrations were used for the first eight alcohols, those of octanol being about 1500-times lower than those of methanol. For each alcohol the D-glucose uptake and the fluidity were linear functions of the logarithm of the concentration, the linear regressions being practically parallel and equidistant. The concentrations (C) of the eight alcohols inhibiting the D-glucose uptake by 80% were similar to those increasing the membrane fluidity by 3%. The linear relationship which existed in both cases between log 1/C and log P, P being octanol/water partition coefficients of the alcohols, was evidence of great sensitivity to the hydrophobic effect of the alcohols. Only the first alcohols, however, produced any notable inhibition of Mg2+-ATPase and sucrase. Hydrophobic bonds are thus shown to have little influence in maintaining the activity of Mg2+-ATPase and sucrase, but they modulate the Na+-coupled D-glucose uptake.

Mesures du métabolisme et de la lyse des cellules épithéliales isolées de l'intestin du rat incubées en présence de divers détergents

Abstract The measurements of metabolism and lysis during the incubation of epithelial cells isolated from small intestine of the rat have proved to be a sensitive test for determining the relative activity of surface-active agents. Triton X-100 and deoxycholate (DOC) are very active at a weak concentration, while the Tweens, in comparison, are much less active; they can be arranged in the following of declining activity: Tween 20, Tween 80 and Tween 60. These surface-active agents decrease cell respiration, but at the concentrations showing a low level of activity a corresponding increase of Q G and Q L is shown at the same time. At high concentration, lysis of the epithelial cells is observed and confirmed by the appearance, in the extracellular medium of proteins, RNA and DNA, these substances later being subject to further enzymatic hydrolysis.

Effet de I’acide tannique sur la sécrétion gastrique chez le rat

We have studied the effect of tannic acid on gastric secretion in the stomach of the rat [Shay et al., 1945]. Using both single and repeated dosages, our findings disclose: The administration of a sin

Carrageenan-induced granuloma and iron status in rats with dietary polyunsaturated fatty acid deficiency

Sprague-Dawley rats were fed for 4 months on a control diet or a polyunsaturated-fatty-acid (PUFA)-deficient diet. The combined effects of iron overload (Fe dextran) or Fe deficiency (desferrioxamine) on carrageenan-induced granuloma were studied. PUFA deficiency induced changes in Fe metabolism, but no alterations in lipid peroxidation variables were observed. Inflammation implied an increase in lipid peroxidation, Fe storage and caeruloplasmin concentration, together with symptoms of anaemia. PUFA deficiency in inflamed rats gave rise to a lower inflammatory response (granuloma weight and prostaglandin E2 concentration) and ethane exhalation. Fe overload potentiated inflammatory and lipid peroxidation processes, whereas Fe deficiency decreased them.

Inhibition of Ca2+ sequestration in foetal liver microsomes by carbon tetrachloride and bromotrichloromethane

The purpose of the present work is to establish to what extent the calcium uptake of foetal liver microsomes can be modified, as in the adult, by classical hepatotoxins. The administration of liver toxins (BrCCl3, CCl4) to the pregnant rat or their addition to foetal and maternal liver microsome preparations causes a decrease in the level of cytochrome P-450 and a drop in the calcium storage capacity of microsomes. Lipid peroxidation of membrane phospholipids is observed in the mother but not in the foetus. On the 20th day of gestation, the foetal liver shows cytochrome P-450 dependent metabolic activity and constitutes a good model illustrating the hypothesis of calcium pump inhibition by .CCl3 radicals without lipoperoxidation.

Implication of membrane functions in toxicology

The following are defined: the structural and biochemical characteristics of the membrane constituents involved in the functional activity; the importance of the environment of the proteins in the expression of their activity; and the adaptation possibilities of the membranes functions to the nutritional distortions or to the action of drugs. The membranes functions, as a hydrophobic barrier and its essential activities, are analysed in relation to their involvement in toxicology with examples of substances having a great specificity of action. On the other hand, the case of substances impairing, in a non-specific way, the membranes functional state, very frequently the case in food toxicology, is analysed through the modification of the hydrophobic interaction forces that they induce. Two membranes playing a key role in food toxicology are especially studied: the enterocyte brush border, of which the essential function is absorption and which represents the first barrier to the component brought by food; and the smooth endoplasmic reticulum, which counts among its essential functions the detoxication of xenobiotics and the control of cytoplasmic Ca2+ concentration. The consequences on these functions of a change of the membranes molecular interaction forces under the in vitro action of a series of substances having different lipophilic power (n-aliphatic alcohols, N-phenyl carbamates, methoxybenzene derivatives) are presented. The consequences of nutritional distortions (ethanol administration or diets deficient in essential fatty acids) on the in vivo adaptation of these membranes under conditions which also modify the membrane interaction forces are also considered.

Toxicocinetique d'un pesticide du groupe des thioquinoxalines: L'oxythioquinox

Abstract Toxicokinetics of a thioquinoxaline component: the oxythioquinox The absorption and distribution of Morestan 35 S in the organism of the rat were studied after administration by stomach tube. It was shown that Morestan, in vivo and in vitro, forms a complex with plasma proteins and particularly with albumins. Most of the plasma Morestan is distributed like this. After intravenous administration, the constant of elimination, K 13 , and the biological half-life determination show that plasma Morestan 35 S is eliminated very slowly. The K 12 and K 21 constants indicate that there is an equilibrium between the plasma compartment and a peripheral compartment. After intragastric administration, the increase of radioactivity in epididymal adipose tissue, indicate that the peripheral compartment should include the adipose tissue.