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Biomedical subjects

L Ramos

Publications and source records attributed to L Ramos.

At least 55 records · Page 3Linked to original sources
PubMed2000

Study of the distribution of the polychlorinated biphenyls in the milk fat globule by supercritical fluid extraction.

The distribution of polychlorinated biphenyls (PCBs) in the milk fat globule has been studied by sequential extraction of four different lipidic fractions from powdered full-fat milk with supercritical carbon dioxide. Extractions were carried out in the dynamic mode in the pressure range 13.6-23.3 MPa at a temperature of 50 degrees C. The levels of PCBs and short-chain triglycerides (SCT), medium-chain triglycerides (MCT) and long-chain triglycerides (LCT), as well as the cholesterol in these four supercritical fluid extraction (SFE) fractions were determined. Extracts obtained at lower pressures were found to be enriched in PCBs, SCT, MCT and cholesterol, while the concentrations of all these analytes decreased for subsequent extractions. Satisfactory quadratic correlations were found between the PCB and SCT and MCT levels (r2 in the range 0.9-0.999), and between the PCB and cholesterol levels (r2 in the range 0.8-0.999, except for PCB 105) determined in the SFE fractions. These results suggested a similar distribution of the PCBs and the cholesterol in the milk fat globule. This conclusion was also supported by the comparison of the PCBs and the cholesterol chemical structures as well as by the total PCB levels determined by SFE to those obtained by using different extraction methods. The classical requirement for the analysis of this kind of lipophilic pollutants of an exhaustive extraction of the lipids of the matrix to ensure their quantitative recovery has been revised.

Animals↗
PubMed2000

A hyperglycemic peptide hormone from the Caribbean shrimp Penaeus (litopenaeus) schmitti.

From a crude extract of the sinus glands of the shrimp Penaeus (litopenaeus) schmitti a peptide with hyperglycemic activity in a homologous bioassay was isolated and characterized by a combination of automatic Edman degradation, enzymatic digestions, TLC of dansyl-amino acids, and mass spectrometry. Its M(r) is 8359.4 Da by MS, which coincides with the deduced sequence. Its N-terminus is free and its C-terminus is amidated. It has 6 Cys residues in conserved positions compared with other known CHHs. This is the first sinus gland hormone from an Atlantic Ocean shrimp characterized to date. It has a remarkable 90% sequence similarity to the Indo-Pacific shrimp P. (marsupenaeus) japonicus Pej-VII hyperglycemic hormone.

Amino Acid Sequence↗
PubMed2000

The inhibition of epidural morphine-induced pruritus by epidural droperidol.

UNLABELLED: IV droperidol inhibits epidural morphine-induced pruritus, but this effect disappears when the dose is increased from 2.5 to 5.0 mg. This study was performed to determine whether epidural droperidol would have a similar effect. In this double-blinded study, we enrolled 140 patients undergoing Cesarean delivery under epidural anesthesia who were randomly allocated to four groups. Anesthesia consisted of 150 mg of 0.5% bupivacaine with 1:200,000 epinephrine, with 2 mg of morphine and 0.0, 1.25, 2.5, or 5.0 mg of droperidol (Groups 1 to 4). During the postoperative period, patients were assessed for pruritus (absent, mild, moderate, or severe) and other untoward symptoms. The chi(2) test was used to compare the incidence of the side effects. For the analysis of pruritus, we used the Mantel-Haenszel test for linear association. Droperidol induced a dose-related reduction in the incidence of pruritus (P < 0.001). This reduction was independent of the incidence of somnolence, which increased with droperidol dose (P < 0.05 when the incidence of somnolence in Groups 1 and 4 was compared). We conclude that droperidol, in doses up to 5 mg epidurally, induces a dose-related reduction in the incidence of pruritus without inducing significant side effects. IMPLICATIONS: Epidural morphine is effective for pain control but yields some side effects, including pruritus, that can be severe. Studying patients undergoing Cesarean delivery, we found a dose-related reduction in the incidence of pruritus using epidural droperidol.

Adult↗
PubMed1999

Surfactant-mediated two-dimensional crystallization of colloidal crystals

Colloidal particles can form unexpected two-dimensional ordered colloidal crystals when they interact with surfactants of the opposite charge. Coulomb interactions lead to self-limited adsorption of the particles on the surface of vesicles formed by the surfactants. The adsorbed particles form ordered but fluid rafts on the vesicle surfaces, and these ultimately form robust two-dimensional crystals. This use of attractive Coulomb interaction between colloidal particles and surfactant structures offers a potential new route to self-assembly of ordered colloidal structures.

Journal Article↗
PubMed1999

Electrostatic repulsion of positively charged vesicles and negatively charged objects

A positively charged, mixed bilayer vesicle in the presence of negatively charged surfaces (for example, colloidal particles) can spontaneously partition into an adhesion zone of definite area and another zone that repels additional negative objects. Although the membrane itself has nonnegative charge in the repulsive zone, negative counterions on the interior of the vesicle spontaneously aggregate there and present a net negative charge to the exterior. Beyond the fundamental result that oppositely charged objects can repel, this mechanism helps to explain recent experiments on surfactant vesicles.

Journal Article↗
PubMed1999

Particle-stabilized defect gel in cholesteric liquid crystals

Dispersions of colloidal particles in cholesteric liquid crystals form an unusual solid by stabilizing a network of linear defects under tension in the ideal layered structure of the cholesteric. The large length scales of the cholesteric liquid crystals allowed direct observation of the network structure, and its properties were correlated with rheological measurements of elasticity. This system serves as a model for a class of solids formed when particles are mixed with layered materials such as thermotropic and lyotropic smectic liquid crystals and block copolymers.

Journal Article↗
PubMed1999

Liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry enantiomeric separation of dl-threo-methylphenidate, (Ritalin) using a macrocyclic antibiotic as the chiral selector.

Vancomycin, a macrocyclic antibiotic, is an amphoteric glycopeptide produced by Streptomyces orientalis which has proven to be a viable chiral selector for high performance liquid chromatograph (HPLC) (D. W. Armstrong, Y. Tang, S. Chen, Y. Zhou, C. Bagwill and J-R. Chen, Anal. Chem. (1994; 66: 1473). While it is related to other glycopeptide antibiotics, vancomycin has a number of unique structural features, including 18 stereogenic centers, five aromatic rings, and two side chains one of which is a carbohydrate dimer. Therefore, a vancomycin-based stationary phase appears to be multimodal in that it can be utilized in both normal-phase and reversed-phase liquid chromatography. Consequently, the enantiomeric separation may be operative via several mechanisms, including pi-pi complexation, dipole stacking, inclusion, hydrogen bonding, or combinations of these interactions. LC/MS/MS is a powerful tool for quantitative analysis when evaluated on the basis of speed, specificity, reliability and sensitivity. For these reasons, the present paper explored the feasibility of bonded macrocyclic glycopeptide phases for chiral LC/MS/MS quantitative analysis. Methylphenidate was used as a model compound. A rapid chiral bioanalytical method (<7.5 min) for the determination of the enantiomers of methylphenidate was developed. A lower limit of quantification (LLOQ) of 87 pg/mL was attained for the human plasma assay. This is to our knowledge the first example of enantioselective reversed-phase LC/MS/MS for methylphenidate. The chiral column was relatively cost effective and exhibited excellent performance with no separation deterioration observed after approximately 2500 injections.

Atmospheric Pressure↗
PubMed1999

Application of liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry in the quantitative analysis of glyburide (glibenclamide) in human plasma.

Glyburide (glibenclamide) is widely prescribed in the treatment of Type II diabetes. A validated liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry (LC/APCI-MS/MS) method for the determination of glyburide is reported. The method uses a stable isotope labeled glyburide as the internal standard. Subsequent to acetonitrile protein precipitation, the supernatant was directly (unfiltered) injected onto the LC column (retention time approximately 3 min) for analysis. A lower limit of quantification (LLOQ) of 1.01 ng/mL was attained for the human plasma assay. The method was fast, specific, and exhibited excellent ruggedness. It was successfully applied to the analysis of clinical samples from patients dosed with glyburide.

Calibration↗
PubMed1999

Comparative study of methodologies for the analysis of PCDDs and PDCFs in powdered full-fat milk. PCB, PCDD and PCDF levels in commercial samples from Spain.

Feasibility of two different extraction methods involving solid-liquid extraction and Soxhlet extraction, previously used for the determination of lipid contents and PCB levels on powdered full-fat milk, are now examined for simultaneous PCDD/F analysis. The results of this study are consistent with those found for PCBs. The solid-liquid procedure provides the most efficient extraction of both labelled spiked and endogenous PCDD/Fs with the lowest variability. The average recoveries were 101% (R.S.D. = 6.9%) for 13C12-2,3,7,8-TCDD and 95% (R.S.D. = 11%) for 13C12-1,2,3,4,7,8-HxCDD. The R.S.D.s for endogenous 2,3,7,8-PCDD/Fs were in the 9.3-25% range. In addition, this methodology simplified the subsequent clean-up step as it allowed a semi-selective extraction of the apolar lipids from the milk. The proposed method was applied to simultaneous PCB and PCDD/F analyses in different brands of powdered full-fat milks commercially available in Spain. In all cases, very similar PCB and PCDD/F levels were found. Differences among batches from the same manufacturer were even lower. The total i-TEQ average for PCDDs and PCDFs in the 22 powdered full-fat milk samples analysed was 1.87 pg/g fat basis. This value was similar to those found in cow's milk from other European countries.

Animals↗
PubMed1999

Levels of PCBs, PCDDs and PCDFs in commercial butter samples in Spain.

Feasibility of three different extraction methods for the simultaneous determination of polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in butter is discussed. The method based on liquid-liquid extraction with water of the non fatty solids from butter dissolved in hexane was found to be the most efficient for the determination of the lipid content and the levels of the investigated pollutants. This method was used to evaluate the background levels of PCBs, PCDDs and PCDFs in butters commercially available in Spain. Broad ranges of PCB, specifically, PCDD and PCDF concentrations were found in the different brands analysed. Levels, profiles and patterns of these pollutants in butter were compared with those previously reported for different Spanish dairy products. The toxic tetra-equivalents of 2,3,7,8-TCDD (1-TEQ) averages for PCDDs and PCDFs in the 21 butter samples analysed were 0.41 and 0.70 pg/g fat basis, respectively. These values were similar or lower than those cited in the literature for other countries.

Benzofurans↗
PubMed1999

Retrieval, maturation, and fertilization of immature oocytes obtained from unstimulated patients with polycystic ovary syndrome.

PURPOSE: Our purpose was to determine whether immature oocytes could be retrieved under local anesthesia, whether these oocytes would mature and fertilize in vitro, and whether adequate endometrium development could be obtained after hormonal supplementation. METHODS: Ovum pick-up was performed under local anesthesia. Immature oocytes were cultured and inseminated. To prepare the endometrium, estradiolvalerate was administered in combination with micronized progesterone. RESULTS: Immature oocytes were obtained in all cases. Fifty-six percent (n = 30) of the oocytes developed into metaphase II (MII) after 48 hr of culture, and another 20% reached the MII stage by 72 hr. Normal fertilization was observed in only 10% of oocytes inseminated. No embryonic development occurred, and therefore embryo transfer was not performed in any of the patients. Endometrial microbiopsy was performed in all subjects and endometrial development was considered sufficient in eight patients. CONCLUSIONS: We collected immature oocytes from patients with polycystic ovary syndrome without general anesthesia. In vitro maturation of these oocytes seemed adequate but fertilization rates were poor. Sufficient endometrial quality was obtained after hormonal substitution.

Adult↗
PubMed1999

Localization of human BRCA1 and its loss in high-grade, non-inherited breast carcinomas.

Although the link between the BRCA1 tumour-suppressor gene and hereditary breast and ovarian cancer is established, the role, if any, of BRCA1 in non-familial cancers is unclear. BRCA1 mutations are rare in sporadic cancers, but loss of BRCA1 resulting from reduced expression or incorrect subcellular localization is postulated to be important in non-familial breast and ovarian cancers. Epigenetic loss, however, has not received general acceptance due to controversy regarding the subcellular localization of BRCA1 proteins, reports of which have ranged from exclusively nuclear, to conditionally nuclear, to the ER/golgi, to cytoplasmic invaginations into the nucleus. In an attempt to resolve this issue, we have comprehensively characterized 19 anti-BRCA1 antibodies. These reagents detect a 220-kD protein localized in discrete nuclear foci in all epithelial cell lines, including those derived from breast malignancies. Immunohistochemical staining of human breast specimens also revealed BRCA1 nuclear foci in benign breast, invasive lobular cancers and low-grade ductal carcinomas. Conversely, BRCA1 expression was reduced or undetectable in the majority of high-grade, ductal carcinomas, suggesting that absence of BRCA1 may contribute to the pathogenesis of a significant percentage of sporadic breast cancers.

Antibodies↗
PubMed1999

Syncope-related trauma: rationale and yield of diagnostic studies.

BACKGROUND: Syncope occasionally occurs in trauma patients. The most appropriate and cost-effective evaluation for such patients is unknown. METHODS: Trauma patients admitted to a Level I trauma center with a diagnosis of syncope or possible syncope between 1988 and 1994 were reviewed. History, physical examination, and past medical history were noted, as were the results of tests done as part of the syncope evaluation. RESULTS: Eighty-eight patients were reviewed; 45% had been injured in falls. Thirteen patients who remembered their entire injury and denied syncope as a cause had negative evaluations. History, physical examination, and admission laboratory values were helpful in diagnosis 59% of the time. Subsequent evaluation provided useful diagnostic information 30% of the time. No patients with normal admission electrocardiograms (EKGs) had cardiac causes for their syncope. CONCLUSIONS: (1) Patients with possible syncope without loss of consciousness require no further evaluation. (2) A cerebrovascular evaluation should be the initial diagnostic approach in patients with signs and symptoms suggestive of stroke or transient ischemic attack. (3) Possible syncope patients with normal admission EKGs should undergo computed tomography of the head and electroencephalography. Those with abnormal EKGs should undergo echocardiography.

Accidental Falls↗
PubMed1998

Determination of polychlorinated biphenyls in soybean infant formulas by gas chromatography.

A method previously developed for the analysis of organohalogenated compounds in dairy products is now validated for polychlorinated biphenyls (PCBs) determination in soybean infant formulas. The results of this study are consistent with those found for PCBs in powdered full-fat milk. The methodology is based on a solid-liquid extraction step enabling a semi-selective extraction of the apolar lipids of the matrix without affecting the efficiency for the recovery of PCBs. Mean recoveries for the spiked coplanar congeners studied were in the 88-114% range, with relative standard deviations (R.S.D.s) lower than 9.8%. The R.S.D.s related to the determination of endogenous PCBs were in the 1.5-10.0% range. The validated methodology was applied to the PCB analysis in different trademarks of soybean infant formulas commercialised in Spain. Toxic tetraequivalents of tetrachlorodibenzo-p-dioxin and daily intake corresponding to each one were calculated and compared with values previously published and with those found in literature for human breast milk in different countries.

Chromatography, Gas↗
PubMed1998

Gas chromatography determination of polychlorinated biphenyls in powdered and liquid soybean milks.

A method previously validated for the analysis of individual congeners of polychlorinated biphenyls (PCBs) in soybean infant formulas is now used to determine PCB levels in dairy-like soybean derivatives, including liquid and powdered soybean milks. Some differences were found among PCB levels and profiles calculated from the different liquid and powdered soybean milks investigated when compared to previously reported for soybean infant formulas, and those most common in dairy-products from Spain and from other countries. PCB levels detected in liquid soybean milks were lower than those found in powdered soybean milks. Levels reported for these two dairy-like derivatives were lower than those detected in soybean infant formulas. The most apparent difference among soybean derivatives and cow's milk was that individual PCB levels detected in the former were lower than those reported for the latter, except for congeners 126 and, specifically, 77, which showed the opposite trend. This feature was common to all soybean products investigated including infant formulas, powdered and liquid soybean milks.

Chromatography, Gas↗