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N Vivas

Publications and source records attributed to N Vivas.

6 recordsLinked to original sources

Development of direct size-exclusion chromatography separation for the determination of molar mass of native procyanidins in the phenolate form.

A size-exclusion chromatographic method using an aqueous solvent as eluent was developed for the determination of the molecular mass of procyanidins has been developed. Size-exclusion chromatography is a chromatographic technique used to determine molecular weight distribution of polymers. During the development work, PL aquagel-OH columns and several different eluent compositions were investigated. The best separation of procyanidins was obtained with an eluent consisting of water-methanol (50:50, v/v), NaNO3: 0.18 M, pH < pKa + 2. The results from this aqueous SEC method were compared with results obtained using SEC with organic solvents.

Calibration↗

Application of off-line size-exclusion chromatographic fractionation-matrix assisted laser desorption ionization time of flight mass spectrometry for proanthocyanidin characterization.

In this work, we wanted to devise a reliable method to characterize polymerized forms of tannins, their structural information and mass distribution. Size-exclusion chromatography (SEC) is a chromatographic technique used to determine molecular mass (weight) distributions of polymers. One important step in the data treatment is the modeling of the calibration curves. Polystyrenes (PS) are standards usually used because no commercial procyanidin (PC) standards are available. An off-line coupling of SEC and MALDI was carried out to measure differences between polystyrenes and procyanidins. Thus, a new calibration curve was established; from 1000 to 8000 Da, there is a good correlation between the MALDI and PS calibration curves, in this field the PS calibration is correct and enables true mass determination. For masses above 8000 Da, PS calibration overestimates the real molecular weight of PC, overestimation of 53%. And for masses below 1000 Da, PS calibration underestimates their real molecular weight (10-15%). This means that to truly characterize PC, calibration based on PC standards is required.

Acetylation↗

Effect of early versus late administration of human recombinant erythropoietin on transfusion requirements in premature infants: results of a randomized, placebo-controlled, multicenter trial.

OBJECTIVE: The administration of recombinant human erythropoietin (rHuEPO), started after the first 2 weeks of life, reduces the transfusion requirement in premature infants. However, its use throughout the first 2 weeks of life, when anemia results predominantly from phlebotomy losses, remains controversial. We investigated whether early use of rHuEPO would reduce the total transfusion requirement and/or the number of transfusions throughout the first 2 weeks of life. METHODS: We randomized 114 infants with birth weight (BW) <1250 g to receive rHuEPO (1250 units/kg/week; IV; early group: n = 57) or placebo (late group: n = 57) from day 2 to day 14 of life; subsequently, all the patients received rHuEPO (750 units/kg/week, subcutaneously) for 6 additional weeks. All infants were given oral iron (6 mg/kg/day) and folic acid (2 mg/day). RESULTS: The early group showed higher hematocrit and reticulocyte counts than the late group in the first 3 weeks of life, but there was no difference in the total number of transfusions (early: 1.8 +/- 2.3 vs late: 1.8 +/- 2.5 transfusion/patient) or the transfusion requirement throughout the first 2 weeks of life (early:.8 +/- 1.1 vs late:.9 +/- 1.3) could be demonstrated. In infants with BW <800 g and total phlebotomy losses >30 mL/kg (n = 29), a lower number of transfusions was received by infants in the early group, compared with late group, from the second week to the end of the treatment (early: 3.4 +/- 1.1 vs late: 5.4 +/- 3.7 transfusion/patient). No clinical adverse effects were observed. Thrombocytosis was detected during the treatment with rHuEPO in 31% of the infants. CONCLUSIONS: In the whole population, the early administration of rHuEPO induced a rise of reticulocyte counts, but not enough to reduce the transfusion requirement. The most severely ill infants (BW <800 g and phlebotomy losses >30 mL/kg) seemed to benefit from early use of rHuEPO, and this deserves additional study.

Anemia, Neonatal↗

Comparative study of polyphenol scavenging activities assessed by different methods.

The effect of procyanidin solutions on superoxide anion radicals was studied with an enzymatic method and their EC(50) values were determined. A comparative study of the results suggested that the free radical scavenger potential of these phenolic compounds closely depends on their chemical and stereochemical structures. Oligomeric procyanidins were isolated in different fractions from grapes and wines by low- and high-pressure liquid chromatography. These compounds were found to be efficient free radical scavengers even for the weak concentrations in wines. Their activity in grapes or wines was much stronger than that of other commercially available natural antioxidants (such as ascorbic acid and gallic acid). The effect of tannins isolated from grapes on different radicals was analyzed according to three distinct methods: an enzymatic method for superoxide anion radicals (O(2)(*)(-)), a chemical method for the stable 1,1-diphenyl-2-picrylhydrazyl radical (DPPH(*)), and an immunochemical method to study the scavenging activity of seed procyanidins on DNA lesions induced by the radical HO(*).

Bepridil↗

Study of the mechanism of the relaxant action of (+)-glaucine in rat vas deferens.

1. Effects of the aporphinoid alkaloid, (+)-glaucine, on rat vas deferens were investigated. 2. (+)-Glaucine (2-18 microM) competitively inhibited contractions induced by noradrenaline and methoxamine with a pA2 value of about 6. 3. (+)-Glaucine (2 and 18 microM) did not change the accumulation of tritium during incubation of the vas deferens with [3H]-noradrenaline. 4. (+)-Glaucine (0.3 nM-0.1 mM) inhibited specific [3H]-prazosin binding to membranes from rat vas deferens with a pKi value of 6.63, which is close to the pA2 value obtained against noradrenaline and methoxamine in functional studies. 5. In electrically-stimulated rat vas deferens, (+)-glaucine (0.3-10 microM) enhanced twitch contractions and competitively antagonized the inhibitory effect of clonidine with a pA2 value of 5.91. 6. In tissues incubated in depolarizing calcium-free high-potassium medium, (+)-glaucine (30-80 microM) inhibited Ca(2+)-induced contractions with depression of the maximal response at higher doses and with a pD'2 value of 3.65. Furthermore, (+)-glaucine (50 microM) did not modify basal 45Ca uptake but strongly inhibited the influx of 45Ca induced by K+. 7. These results suggest that (+)-glaucine has non-selective alpha 1- and alpha 2-adrenoceptor blocking properties. At higher doses, (+)-glaucine shows calcium antagonist activity which may be responsible, at least in part, for the inhibition of the contractions induced by Ca2+ in calcium-free high-potassium medium.

Animals↗