Biomedical subjects

E Samain

Publications and source records attributed to E Samain.

42 records · Page 3Linked to original sources

PubMed1990

Desensitization of myocardial beta-adrenergic receptors in cirrhotic rats.

Cardiac responses to catecholamines are known to be attenuated in chronic liver disease. To elucidate the role of beta-adrenergic receptor alteration in this phenomenon, we measured heart rate responsiveness to isoprenaline and myocardial beta-adrenergic receptor-binding characteristics in three groups of rats: those that were sham operated, those that had portal vein stenosis and those that were cirrhotic because of bile duct ligation. Responsiveness to isoprenaline was evaluated in conscious rats by the dose of isoprenaline needed to increase basal heart rate by 50 beats/min and by the maximal heart rate response. beta-Receptor characteristics in heart membranes were derived from 125I-iodocyanopindolol binding data. Compared with sham-operated controls, cirrhotic rats needed a significantly higher dose of isoprenaline to raise basal heart rate by 50 beats/min (102.3 +/- 19.1 vs. 28.3 +/- 11.3 ng/kg) and lower maximal heart rate response (104 +/- 29 vs. 158 +/- 61 beats/min). In addition, myocardial beta-receptor density was significantly lower in cirrhotic rats (26.5 +/- 4.6 vs. 37.5 +/- 10.3 fmol/mg protein) and the dissociation constant was higher (31.6 +/- 17.0 vs. 14.0 +/- 2.5 pmol/L). Analysis of beta 1/beta 2 subpopulations revealed that the decreased total beta-receptor density was entirely due to selective beta 1-receptor down-regulation. beta-Receptor affinity for agonist was not altered in cirrhotic rats. Rats with portal vein stenosis showed no significant differences in either isoprenaline responsiveness or beta-receptor characteristics when compared with controls. These results indicate that beta-adrenergic receptor down-regulation may be responsible for the myocardial hyporesponsiveness to catecholamines observed in cirrhosis.

Animals↗

PubMed1989

Effects of propofol on baroreflex control of heart rate and on plasma noradrenaline levels.

The effects of propofol induction (2.5 mg kg-1) and of two continuous infusion rates of propofol (100 and 200 micrograms kg-1 min-1) on baroreflex control of heart rate and on plasma noradrenaline concentration were investigated in 11 unpremedicated patients. Baroreflex function was assessed using a pressor test (phenylephrine) and a depressor test (sodium nitroprusside). In addition, samples for subsequent determination of plasma noradrenaline levels and blood propofol levels were collected before each test. Baroreflex sensitivity and plasma noradrenaline concentrations were not significantly changed at any time of the study. By contrast, a significant and sustained resetting of baroreflex set point was observed, allowing unchanged heart rate at lower arterial pressure. It is concluded that the effects of propofol on baroreflex function and noradrenaline concentration are moderate.

Adult↗

PubMed1988

Reductive carboxylation of propionate to butyrate in methanogenic ecosystems.

During the batch degradation of sodium propionate by the anaerobic sludge from an industrial digestor, we observed a significant amount of butyrate formation. Varying the initial propionate concentrations did not alter the ratio of maximal butyrate accumulation to initial propionate concentration within a large range. By measuring the decrease in the radioactivity of [1-C]butyrate during propionate degradation, we estimated that about 20% of the propionate was converted to butyrate. Labeled butyrate was formed from [1-C]propionate with the same specific radioactivity, suggesting a possible direct pathway from propionate to butyrate. We confirmed this hypothesis by nuclear magnetic resonance studies with [C]propionate. The results showed that [1-C]-, [2-C]-, and [3-C]propionate were converted to [2-C]-, [3-C]-, and [4-C]butyrate, respectively, demonstrating the direct carboxylation on the carboxyl group of propionate without randomization of the other two carbons. In addition, we observed an exchange reaction between C-2 and C-3 of the propionate, indicating that acetogensis may proceed through a randomizing pathway. The physiological significance and importance of various metabolic pathways involved in propionate degradation are discussed, and an unusual pathway of butyrate synthesis is proposed.

Journal Article↗

PubMed1987

Isolation of succinate dehydrogenase from Desulfobulbus elongatus, a propionate oxidizing, sulfate reducing bacterium.

Succinate dehydrogenase was purified from the particulate fraction of Desulfobulbus. The enzyme catalyzed both fumarate reduction and succinate oxidation but the rate of fumarate reduction was 8-times less than that of succinate oxidation. Quantitative analysis showed the presence of 1 mol of covalently bound flavin and 1 mol of cytochrome b per mol of succinate dehydrogenase. The enzyme contained three subunits with molecular mass 68.5, 27.5 and 22 kDa. EPR spectroscopy indicated the presence of at least two iron sulfur clusters. 2-Heptyl-4-hydroxy-quinoline-N-oxide inhibited the electron-transfer between succinate dehydrogenase and a high redox potential cytochrome c3 from Desulfobulbus elongatus.

Bacteria↗

PubMed1985

Influence of calcium addition on growth of highly purified syntrophic cultures degrading long-chain Fatty acids.

Two highly purified syntrophic associations resulting in acetogenesis from stearate (SM) and oleate (OM) were obtained from the sludges of a sewage digestor. In both cases, Methanospirillum hungatei together with short, motile, gram-negative, nonfluorescent rods morphologically similar to Syntrophomonas wolfei were identified by microscopic examination. Besides growing on volatile fatty acids (butyrate through caproate), both cultures grew on oleate (C(18:1)) and numerous even-numbered, saturated long-chain fatty acids (LCFA [decanoate through stearate]). In addition, during growth on LCFA, supplementation of the culture media with calcium chloride was an absolute requirement. The sole difference between the associations was observed when SM and OM cultures were transferred from a stearate to an oleate medium. The SM culture needed 10 days before starting to degrade oleate, whereas the OM culture grew immediately, but the OM culture also grew immediately when transferred to stearate medium. Saturated LCFA degradation occurred in the presence of equinormal amounts of calcium (fatty acid/Ca ratio, 2). On the other hand, OM degradation only took place in the presence of an equimolar amount of calcium (fatty acid/Ca ratio, 1). These observations are discussed by considering the solubility constants of LCFA as calcium salts and the toxicity of the free acids against microorganisms.

Journal Article↗

PubMedDate not supplied

[Role of extracellular matrix in angiotensin II signalling in aortic smooth muscle cells: relationship with arterial hypertension].

Angiotensin II (Ang II) is involved in hypertension-related arterial wall hypertrophy [1]. Regulation of AT II transduction pathway in vascular smooth muscle cells (VSMC) may involve cytoskeleton and extracellular matrix (ECM) [2]. We assessed the role of components of ECM on Cai2+ increase induced by Ang II in Wistar-Kyoto (WKY) and Spontaneously Hypertensive Rats (SHR) aortic VSMC. The effect of Ang II (1 mumol) on Ca2+ mobilization was studied in cultured VSMC isolated from the aorta of 6-wk old WKY (MAP (m +/- SE) = 98 +/- 4 mmHg) and SHR (136 +/- 5 mmHg; p < 0.05), using fluorescent imaging microscopy (Fura-2 AM). Cai2+ release from internal stores and Ca2+ influx were assessed in the absence and upon reintroduction of external Ca2+ respectively. Cells were cultured on uncoated glass coverslips (control) or coated with either collagen I (10 micrograms/mL), collagen IV (7 micrograms/mL), vitronectin (0.1 microgram/mL), fibronectin (3 micrograms/mL) and extracellular matrix extract (matrigel, 1/10) and studied at confluence. Paxillin was located in cells by indirect immunofluorescence micrography. Results are expressed in % of Control. Statistical significance (p < 0.05) was assessed with Student's t-test for unpaired data. The effects on Ang II-induced Ca2+ mobilization of growing cells on ECM are in Table. Paxillin in Control cells appeared as dots at the cell boundaries. Density increased in cells grown on collagen I with a diffuse distribution in the WKY cells. On matrigel, paxillin was located in a belt-like fashion at the periphery of the cell. These effects were not linked to differences in cell cycle (flux cytometry).

Angiotensin II↗