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Biomedical subjects

H Lopez

Publications and source records attributed to H Lopez.

At least 37 records · Page 2Linked to original sources
PubMed1994

Overproduction of a low-affinity penicillin-binding protein and high-level ampicillin resistance in Enterococcus faecium.

Five ampicillin-resistant clinical isolates of Enterococcus faecium were analyzed for a correlation between overproduction of the low-affinity penicillin-binding protein (PBP 5) and the level of ampicillin resistance. Comparison was made with one susceptible clinical isolate and its ampicillin-resistant derivative obtained in the laboratory by selection with increasing concentrations of penicillin. Overproduction of the low-affinity PBP relative to the susceptible isolate was noted in moderately resistant strains (MIC, 32 micrograms/ml) but not in highly resistant strains (MIC, 128 micrograms/ml). Polyclonal antibodies specifically reacting with the low-affinity PBP of Enterococcus hirae, Enterococcus faecalis, and Enterococcus faecium (M. Ligozzi, M. Aldegheri, S. C. Predari, and R. Fontana, FEMS Microbiol. Lett. 83:335-340, 1991) were used to determine the amount of this PBP in the E. faecium isolates. In all strains, the antibody preparation reacted with a membrane protein of the same molecular mass as PBP 5. The amount of this protein was very small in the susceptible strain but large in all of the resistant strains. These results suggest that the highly resistant strains also overproduced the low-affinity PBP, which, compared with PBP 5 of moderately resistant strains, appeared to be modified in its penicillin-binding capability.

Ampicillin Resistance↗
PubMed1993

Variability of the QTc interval: impact on defining drug effect and low-frequency cardiac event.

Prolongation of the QT interval corrected for heart rate (QTc) can lead to the development of torsades de pointes, a life-threatening form of polymorphic ventricular tachycardia. However, the QTc interval duration exhibits a high degree of spontaneous variability and is not necessarily a direct predictor of the risk of torsades. This observation holds implications for the assessment of the potential proarrhythmic effects of noncardiac pharmacologic agents. To date, the antihistamine terfenadine is the only noncardiac drug that has undergone a comprehensive and systematic evaluation related to the consequences of its causing QTc prolongation. The results suggest that QTc prolongation resulting solely from terfenadine at clinical doses does not have an important impact on clinically relevant endpoints. The risk of serious ventricular arrhythmias with terfenadine using epidemiologic data is the same or less than that associated with traditional first-generation antihistamines. The risk of a clinical cardiac event (QTc prolongation, ventricular arrhythmias, syncope, or sudden death) with terfenadine is similar to that of other antihistamines. Factors associated with increased risk in patients taking terfenadine include significant liver disease, hypokalemia, overdose, and concomitant administration of ketoconazole-like agents or erythromycin; use of terfenadine is relatively contraindicated in these settings. No increased risk of serious arrhythmias has been confirmed in conjunction with the use of terfenadine in patients with cardiac disease.

Adult↗
PubMed1991

Rheumatic manifestations in populations at risk for HIV infection: the added effect of HIV.

We assessed the frequency and variability of rheumatologic manifestations in 2 populations with similar risk factors for human immunodeficiency virus (HIV) infection, of which only one was affected. We studied 2 populations at risk for HIV infection (homosexual and intravenous drug users). Group A: 89 individuals carried the virus; and Group B: 80 individuals were HIV negative. In Group A (HIV+) 66.1% had rheumatic manifestations including arthralgias, Reiter's syndrome, arthritis, enthesitis, psoriatic arthritis, Sjögren's syndrome, myopathy, septic arthritis, and lupus-like illness. In contrast, in Group B (HIV-) only 2 had arthralgias, 2 Reiter's syndrome, and 1 rheumatoid arthritis. In summary, rheumatic complaints are common in patients with HIV, and HIV positivity confers an increased susceptibility in populations with similar risk factors for HIV infection.

Adolescent↗
PubMed1989

Bradykinin inhibits a potassium M-like current in rat pheochromocytoma PC12 cells.

We studied the action of bradykinin (BK) on ionic currents in fused pheochromocytoma PC12 cells under voltage-clamp in whole-cell mode, and on intracellular calcium using fura-2 BK induced the development of an outward current associated with an increase in intracellular calcium, followed by inhibition of an M-like current. The outward current was blocked by (+)-tubocurarine, and prevented when the calcium BAPTA or high concentrations of inositol 1,4,5-triphosphate were introduced into the cell, whereas the M-like current and its inhibition by BK remained unaffected. The protein kinase activator phorbol 12,13 dibutyrate partially reduced the M-current. M-current density did not substantially change after prolonged treatment with nerve growth factor.

Animals↗
PubMed1989

New contrast-detail phantoms for improved precision in lesion detection measurements.

The previous design of our ultrasound contrast-detail (C-D) phantom is limited in its ability to evaluate the quality of diagnostic ultrasound imaging systems. There is uncertainty in the contrast-detail measurements due to the single available viewing angle for each target and the resulting single realization of the ultrasound speckle pattern. Two new contrast-detail phantom designs are described which enable many independent realizations of the speckle noise for observer C-D experiments of improved precision. In the first design, a single tissue-mimicking cone is located on the axis of a tissue-mimicking cylinder. Cross-sectional images of the cone which simulate focal lesions can be obtained from any orientation by rotating the cylinder under the transducer. In the second new design, a tissue-mimicking cone is positioned in a tissue-mimicking slurry of agar/graphite spheres. Gentle stirring of the slurry and rotation of the cone produce many independent realizations of the speckle. In both new phantoms, the lesion contrast can be specified and is frequency/transducer independent.

Equipment Design↗
PubMed1988

A method to assay fluoride in foods, beverages, and diets.

Foods and beverages containing sugars, frequently consumed as snacks between meals, contribute to dental caries in different proportions depending on a number of intrinsic factors, including carbohydrate content, textural properties, and mineral composition, such as calcium, phosphate, and fluoride concentration. A method to assay fluoride in foods and beverages is described which involves [1] an acid hydrolysis at 110 degrees C in a closed vial with a valve for dispensing reagents and [2] estimation of total acid-hydrolyzed fluoride using a specific ion electrode. A number of foods, beverages, and diets were analyzed for acid-hydrolyzable and free fluoride. The simplicity of the method eliminates fluoride contamination, making the procedure accurate and reproducible in determining fluoride in foods and beverages.

Beverages↗
PubMed1987

Toxicity and immunogenicity of monoclonal antimelanoma antibody-ricin A chain immunotoxin in rats.

This study was performed to assess the subacute toxicity and immunogenicity in rats of XOMAZYME-MEL, an antimelanoma monoclonal antibody-ricin A chain immunotoxin. Female Sprague-Dawley rats received 14 consecutive daily i.v. injections of XOMAZYME-MEL at doses of 5 mg/kg/day, 1 mg/kg/day, or normal saline. Animals from each dose group were sacrificed on days 8, 15, and 22. The low dose of immunotoxin was well tolerated and produced only minimal signs of toxicity. Side effects in animals receiving the high dose of immunotoxin consisted of transient weight loss, peripheral edema, leukocytosis, hypoalbuminemia, and mildly elevated liver function tests. Histological findings in these animals included cytoplasmic vacuolization of hepatocytes, focal myocardial and skeletal muscle degeneration, and renal deposits of proteinaceous casts. The administration of immunotoxin resulted in the appearance of anti-mouse and antiricin A chain immunoglobulin binding activity in the sera of treated animals. This study documents the systemic effect of the multiple-dose administration of a ricin A chain immunotoxin in rats.

Animals↗
PubMed1987

Effect of cyclophosphamide on the immunogenicity of monoclonal antimelanoma antibody-ricin A chain immunotoxin in rats.

This study was performed to determine the effect of treatment with cyclophosphamide (CY) on the formation of antimurine and anti-ricin A chain antibodies in rats treated with a murine monoclonal antimelanoma antibody-ricin A chain immunotoxin (IT). Animals received treatment with either IT alone or IT plus CY. IT treatment consisted of daily IV injections at a dose of 1 mg/kg/day on days 0, 1, 2, 3, 4. CY treatment consisted of a 25 mg/kg IP dose on day -1 followed by daily IP doses of 5 mg/kg/day on days 0, 1, 2, 3, 4. Antibody binding activities in treated animals were measured by enzyme-linked immunosorbent assay and reported as optical density values. Rats treated with IT plus CY had lower binding activity on day 7 (0.09 vs 0.6; p = .02), day 14 (0.42 vs 1.22; p = .001), and day 21 (0.11 vs 1.3; p = .001) compared to rats treated with IT alone. Lower levels of anti-ricin A chain binding activity were observed in CY treated rats on day 14 (0.35 vs 1.25; p = .001), but not on day 7 or day 21. These results indicate that treatment with CY can abrogate the immune response to murine antibody and partially abrogate the immune response to ricin A chain.

Animals↗
PubMed1983

Rat caries assay of reference foods and sugar-containing snacks.

Using standard reference snack foods, we tested a method, using rats fed in a programmed feeding machine, to evaluate the caries-promoting properties of foods. Results, which were expressed in relation to a control food, indicate that the method distinguished differences in caries potential among a number of different snack foods. Buccal and sulcal caries scores of rats fed snacks foods varied in their responses. A gel diet used to provide essential nutrients for the rat growth in this approach contributed minimally to the caries response which was related principally to the food being tested.

Animals↗
PubMed1982

Transient repression of erythromycin formation in Streptomyces erythraeus.

The effect of a D-glucose on growth and erythromycin production by Streptomyces erythraeus was investigated. D-Glucose stimulated growth and caused a strong but temporary suppression of antibiotic formation. Maximum specific suppression of erythromycin formation occurred at a carbohydrate concentration of 20 mg ml-1. A non-metabolizable analogue of glucose, 2-deoxy-D-glucose, also suppressed antibiotic formation. Since glucose caused a decrease in erythromycin formation only when added before the stage of antibiotic production, we conclude that this sugar exerted a transient repressive effect on erythromycin biosynthesis.

Deoxyglucose↗
PubMed1982

[Necessities and possibilities for the prevention of cardiovascular and pulmonary diseases in childhood and adolescence].

In an exploratory study involving 818 pupils 12-16 years of age blood pressure, total serum cholesterol, and smoking behavior were studied. 38.3% of the boys (N = 154) and 47.3% of the girls (N = 143) aged 15-16 demonstrated singular or combined elevated risk variables, cigarette smoking being the most predominant risk factor. 44.5% of the pupils of this age group answered to be regular smokers. 59.8% (N = 183) of secondary school pupils stated to be regular smokers as compared to 15.7% (N = 166) of grammar school pupils. The most important socialpsychological process variables were attitude of friends towards smoking, smoking experience of friends, and social function of smoking within groups. The importance of these variables showed differences according to type of school as well as gender which should be taken into account modelling preventing programmes.

Adolescent↗
PubMed1981

Biological rat assay for total fluoride availability in foods.

A fluoride (F) bioassay procedure based on the method of standard additions and using weanling rats was designed and tested. Rats were distributed between a control (C) group fed MIT 200 diet (F conc. less than 0.5 ppm) and an experimental (E) group fed this diet plus 1% dehydrated instant tea used as a model test food. Both groups were further divided into subgroups fed the C or E diets, but supplemented with 0.5, 10, 20 or 40 ppm F as NaF, and offered deionized water for a period of 10 days. Rats were then killed and femur (fm) and tibia (tb) dissected. Bone samples were treated in a closed system with HCl (6 N) and later with sodium citrate (30%) to determine F concentration using a specific ion electrode. F values (y) for fm and tb were plotted against F amounts added to the diets (xt). Weighted regression equations describing the linear relationship between the two variables were used to calculate the available F content of dehydrated tea which was 830 +/- 43 ppm F (using fm data) and 836 +/- 67 ppm (using tb data). Chemical assay of the dehydrated tea used as a test food gave a F concentration of 887 +/- 16 or 93.5 +/- 5.1% availability. This rat bioassay to determine total available fluoride in a dried food can be combined with a chemical assay to obtain a measure of percent availability of F.

Animals↗
PubMed1977

Sources of variability in rat caries studies: weaning age and diet fed during tooth eruption.

A factorial design (2x2) was used to study the caries effect of two diets (starch based versus stock) fed to rat dams and their litters, and also of variations in the weaning age (19 versus 25 days). Higher and reproducible caries scores were obtained in rats which were fed a purified starch-based diet, weaned at 19 days of age, and subsequently given a cariogenic challenge.

Age Factors↗