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Biomedical subjects

Y Fernandez

Publications and source records attributed to Y Fernandez.

At least 19 recordsLinked to original sources
PubMed1992

Molecular mechanical study of the stability of the Lys-Ala-Ala tripeptide dimer.

A molecular mechanical study of two Lys-Ala-Ala tripeptide chains in interaction is presented. The study was carried out to explore the feasibility of dimer formation and explain some features of the crystal structure not completely understood. The role of the counterions present in the crystal structure on the conformation has been included in this study by investigating the effect of removing the charges on the lysyl side chains. The results of the present molecular mechanical study explains well the structural features found by X-ray crystallography, complementing that study.

Amino Acid Sequence↗
PubMed1992

Superoxide anion scavenging capacity measured by a polarographic method. Comparison with a colourimetric method.

A polarographic method to assess the scavenging capacity of a molecule for O2-. is proposed. This method is based on the fact that O2-. is not detected by the Clark electrode and that a scavenger competes with spontaneous dismutation of O2-. So, the reduction of O2 into O2-. and the decomposition of H2O2 by catalase, releasing O2, show a biphasic kinetic. Various kinetic parameters can be used to calculate the nmol of O2-. scavenged and also supply data on the reaction mechanisms (oxidation or reduction of O2-.) involved in scavenging. This method presents several other advantages: scavenging capacity can be assayed without added indicators which themselves behave as scavengers (as demonstrated for NBT), the presence of scavengers which interfere with the O2-. generating system (xanthine-xanthine oxidase) does not invalidate the measurements made.

Anions↗
PubMed1991

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.

Animals↗
PubMed1991

[Value of hepatic angioscintigraphy combined to pulsed Echo-Doppler: application to the study of portal hypertension of cirrhotic patients. Apropos of 148 cases].

Quantitative hepatic angioscintigraphy was combined with duplex Doppler in order to study liver perfusion in normal subjects and in 148 patients with liver cirrhosis. The portal component of liver perfusion determined by scintigraphy was reduced in patients with liver cirrhosis and correlated to the development of cirrhosis and to porto-hepatic gradient pressure. Duplex Doppler allowed assessment of portal blood direction. Determination of portal blood flow was possible in only a few patients: portal blood flow was increased in the first stage of cirrhosis and then decreased; hepatofugal flow was observed only in the most severe stage. Angioscintigraphy and Duplex Doppler appear to be complementary in the study and follow-up of portal hypertension.

Adult↗
PubMed1990

[A new strategy of neonatal screening for cystic fibrosis. The association of immunoreactive trypsin and molecular biology in dried blood].

Cystic fibrosis (CF) screening by means of immunoreactive trypsin (IRT) lacks specificity: only 1 out of 12 hypertrypsinemic neonates has cystic fibrosis. We propose here to analyse the KM.19 polymorphic site in the dried blood spots as an additional test in hypertrypsinemic neonates. A blind retrospective study of 114 hypertrypsinemic samples has been performed after polymerase chain reaction. Twenty-seven of 37 CF (74%) were homozygous for allele 2 (2-2) and could have been diagnosed on the 15th day of life. Fifty-five percent of the infants tested were homozygous for allele 1 (1-1), a very rare feature in CF, conferring them a probability of being normal of 99.8%. At the moment, this test could be of great help in the CF screening, even better than the search for the delta F508 mutation for which 45.9% of CF patients are homozygous.

Cystic Fibrosis↗
PubMed1988

Activity of liver microsomal Ca2+-ATPase in relation to perturbation of membrane hydrophobic interactions induced by methoxybenzene derivatives and n-aliphatic alcohols.

Changes in the activity of liver microsomal Ca2+-ATPase were studied in the presence of two series of lipophilic compounds: four flavouring substances derived from methoxybenzene and four n-aliphatic alcohols. With each compound the activity was stimulated at lower concentrations and inhibited at higher concentrations. The linear relationship between equiactive concentrations of the compounds and their partition coefficients showed that the enzyme activity was modulated by perturbation of membrane hydrophobic interactions. Measurements carried out by electron-spin resonance (ESR) showed evidence of a decrease in the membrane order induced by these compounds. However, results obtained with the methoxybenzene derivatives showed that the modification in ATPase activity cannot be directly related to the decrease in membrane order. This decrease did not only reflect perturbation of hydrophobic interactions.

Alcohols↗
PubMed1988

The effect of dietary essential fatty acid deficiency on the composition and properties of the liver microsomal membrane of rats.

The effect of dietary essential fatty acid (EFA) deficiency on lipid composition, fluidity and important enzyme and transport activities of liver microsomal membrane was studied in weanling rats. After 133 d of EFA deficiency, no difference was noticed in membrane phospholipid, cholesterol and protein levels, but a significant change occurred in the fatty acid composition of bilayer phospholipids. In EFA-deficient rats, linoleic (18:2(n-6] and arachidonic (20:4(n-6] acids were both severely lower while oleic (18:1(n-9], palmitoleic (16:1(n-7] and particularly 5,8,11-eicosatrienoic (20:3(n-9] acids were significantly higher than in controls. The higher level of the latter tended to compensate for the lower level of 20:4(n-6). Membrane fluidity, as estimated by the reciprocal of the order parameter S, was lower in the deficient rats than in the controls, and all the measured microsomal enzyme activities were markedly affected. NADH-Cyt b5 electron transferring system, coupled with the fatty acid desaturation system, was higher than in controls. In contrast, the cytochrome P450 complex activity was lower and some of the important liver detoxifying enzyme activities were lower due to physical-chemical changes in the microsomal membrane. Calcium uptake and Ca2+-ATPase activity were also significantly lower in EFA-deficient rats than in controls. It was concluded that fatty acid composition may be the major factor contributing to membrane fluidity and function and that EFA might play a role in regulating the intrinsic membrane protein activities.

Animals↗
PubMed1988

Free triiodothyronine measured in dried blood spots from normal, low-birth-weight, and hypothyroid neonates.

Free triiodothyronine (FT3) has rarely been studied in neonates, primarily because of obvious problems in obtaining serum samples from neonates for research purposes. We adapted an analog radioimmunoassay for measuring FT3 in dried blood samples and used it to assay 361 samples selected from those collected for the screening for neonatal hypothyroidism. The mean FT3 concentration in healthy neonates on the fourth postpartum day is 2.55 pmol per liter of whole blood (SD 0.78 pmol/L, n = 145), the same as in healthy adults. Low-birth-weight infants have a decreased concentration of FT3, and this decrease is much greater in premature neonates than in infants at low weight for gestational age. In six hypothyroid newborns, the FT3 concentration was normal or increased, clearly indicating that FT3 assay is not a diagnostic tool for hypothyroidism. FT3 was barely detectable in one case of congenital galactosemia.

Humans↗
PubMed1987

Amniotic immunoreactive trypsin in pregnancies with normal and pathological outcomes.

Immunoreactive trypsin (IRT) has been studied in amniotic fluid as a possible complementary test substance for the prenatal diagnosis of cystic fibrosis (CF). 219 normal amniotic fluids have been tested in order to establish the normal ranges from 14 to 40 gestational weeks (g.w.). The IRT level increases from g.w. 14 to 19, remains stable from g.w. 19 to 25 and then decreases rapidly to low levels. A retrospective study of 4 presumed CF fluids, as determined by abnormal alkaline phosphatase levels, showed decreased IRT values in 3 out of 4 fluids. The difference between the mean value and the normal mean was not significant. The prospective study allowed us to test 2 fluids from pregnancies affected by meconium ileus. IRT level was highly elevated, 530 times the normal mean value at g.w. 34 for a non-CF fetus and 18 times the normal mean value for a CF fetus at g.w. 31. In 4 out of 5 cases of fetal severe intra-uterine growth retardation, IRT levels appeared mildly elevated. Other abnormalities are reviewed.

Amniotic Fluid↗
PubMed1987

[Hemodynamic study of obstructive lesions of the internal carotid artery: value of coupled measurement of regional cerebral blood flow and volume].

A study of 130 patients having presented either a transient ischemic attack or a completed stroke, or admitted for an asymptomatic carotid stenosis, allowed the following investigations: CT-scan, doppler, angiography, measurement of the regional cerebral blood flow (rCBF) by the study of 133Xe clearance (Novocerebrograph (R)), and measurement of the regional cerebral blood volume (rCBV) made by gamma emission tomography after autotransfusion of 99m Tc-labeled erythrocytes with an Elscint Apex 415 ECT (R) camera. Our aim was to look in which case a rCBF and/or a rCBV interhemispheric asymmetry was observed, by comparing the previous hemodynamic parameters with clinical, CT-scan and angiographic data. Although a rCBF and/or a rCBV asymmetry appeared more often among patients presenting with infarction than among those of the asymptomatic category, this does not seem specific for any clinical grade. The same statement applies to the comparison between hemodynamic parameters and CT data. The arterial lesions were classified in 4 groups: no stenosis (12 cases), uni or bilateral moderate carotid stenosis (40 cases), unilateral severe carotid stenosis or occlusion (65 cases), bilateral carotid severe stenosis or occlusion (13 cases). We observed a rCBF asymmetry among some patients in the 4 groups, although this was more frequent among the two latter groups. Nevertheless no case of a rCBV asymmetry was observed in the 2 first groups. Such an asymmetry was present in 31 percent of the patients belonging to the two latter groups. In patients of the third group the asymmetry was always due to a relative increase of rCBV beyond the carotid lesion.(ABSTRACT TRUNCATED AT 250 WORDS)

Arterial Occlusive Diseases↗
PubMed1986

Na+-coupled D-glucose uptake and membrane order of enterocyte brush border membrane vesicles, under the effect of a series of N-phenylcarbamates.

The importance of the hydrophobic effect of exogenous substances and of modifications of membrane order on D-glucose uptake are still poorly defined. Our results show that the concentrative Na+ -coupled D-glucose uptake of rat enterocyte brush border membrane vesicles is inhibited by N-phenylcarbamates increase the membrane order. However, since the concentrations required for membrane order increase are much greater than those active on D-glucose uptake, the effects on lipid order cannot be responsible for the inhibition of D-glucose uptake. Measurements of D-glucose uptake under conditions of Na+ equilibrium show that these carbamates do not act directly on the carrier but indirectly by favouring the dissipation of the Na+ gradient.

Animals↗
PubMed1985

Free thyroxin measured in dried blood spots: results for 10 000 euthyroid and 29 hypothyroid newborns.

We measured free thyroxin (FT4) in dried blood samples from 10 000 euthyroid and 29 hypothyroid newborns (three with transient hypothyroidism and 26 permanent). In euthyroids, the mean FT4 concentration was 16.9 (SD 4.5) pmol/L. Preterm babies had low concentrations of FT4, and values were closely related to birth weight when less than 2500 g. Assay of blood-spot FT4 appears to be specific as a test for hypothyroidism screening, yielding 0.42% false positives when a mean minus 2 SD cutoff value (8 pmol/L) was used. Correcting FT4 for birth weight further decreased the false-positive rate, to 0.07%. In all three newborns with transient hypothyroidism, FT4 was less than 8 pmol/L. In 25 of 26 permanent hypothyroids, FT4 ranged from undetectable to 5 pmol/L; in the 26th infant, who had a large ectopic gland, it was 8.2 pmol/L. We believe that FT4 assay offers an attractive improvement over total T4, whether performed as the first screening test or as a confirmatory test in thyrotropin screening programs.

Birth Weight↗
PubMed1984

Thermodynamic interpretation of effects of alcohols on membrane lipid fluidity.

The effect of a series of amphiphilic compounds, the first eight n-aliphatic alcohols, on the fluidity of rat enterocyte brush border was determined by ESR using 5-doxyl stearic acid as a lipid spin probe. Packing order variations are compared to the relative hydrophobic effect of the alcohols. The concentrations, [Ci]5 of each alcohol that decrease the membrane 2T' value by 5%, vary by a factor of 1500 from methanol to octanol. From [Ci]5, the membrane concentrations Cm and the variation of free energy delta F degree due to the incorporation of the alcohols in the lipids, were calculated. These calculations were performed taking into account the respective volumes of the aqueous phase and the membrane lipids. Cm is of the order of 0.18 mol/kg for the odd chain length alcohols and of 0.27 mol/kg for the even alcohols. The value of delta F degree in cal/mol -CH2- is -687 cal on average for the eight alcohols. This work shows that for all the alcohols, the concentrations at equilibrium in the membrane and in the aqueous phase are respectively in agreement with Meyer and Overton's theory and with the gradient of free energy which constitutes the most general index of interaction of lipophilic substances with membranes.

Alcohols↗