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Biomedical subjects

R Lopez

Publications and source records attributed to R Lopez.

At least 163 records · Page 9Linked to original sources
PubMed1987

Transplantation of cultured rabbit retinal epithelium to rabbit retina using a closed-eye method.

We have developed a closed-eye technique for transplanting cultured rabbit retinal epithelial cells to Bruch's membrane of the rabbit. A glass micropipette containing a suspension of 3H-thymidine-labeled, cultured retinal pigment epithelial (RPE) cells is inserted through a pars plana incision and positioned adjacent to the neural retina. A jet stream from the pipette is used to make a small retinal hole and bleb detachment. Patches of host retinal epithelium lift off with the neural retina, creating areas of bare Bruch's membrane. The cell suspension is injected into the subretinal space, and labeled cells can be seen attached to Bruch's membrane as early as 1 hr later. The neural retina spontaneously reattaches within 24 to 48 hr, bringing photoreceptor outer segments in direct contact with the transplanted cells. Phagocytosis of outer segment material by transplanted cells can be seen as early as 24 hr after surgery. This closed-eye technique offers an advantage over the open-sky method used previously in that it allows for reattachment of the neural retina and at least a partial return of function in the transplanted retinal epithelium.

Animals↗
PubMed1986

Searching for autolysin functions. Characterization of a pneumococcal mutant deleted in the lytA gene.

The first mutant of Streptococcus pneumoniae showing a complete deletion in the lytA gene coding for the N-acetylmuramyl-L-alanine amidase has been isolated and characterized. This amidase was previously the only autolysin detected in this species. This mutant shows a normal growth rate and can be transformed using either chromosomal or plasmid DNA. The most remarkable biological consequences of the absence of the amidase are the formation of small chains (six to eight cells) and the absence of lysis in the stationary phase of growth. In addition, this mutant exhibits a tolerant response against the beta-lactam antibiotics.

Amidohydrolases↗
PubMed1986

Mutants of Streptococcus pneumoniae that contain a temperature-sensitive autolysin.

Two mutants of Streptococcus pneumoniae deficient in autolysin activity produced a protein that showed immunological identity with the N-acetyl-muramyl-L-alanyl-amidase present in the wild-type strain, when tested with antiserum obtained against this enzyme. The protein was produced by the mutant cultures grown either at 37 degrees C or at 30 degrees C, although only the cell extracts obtained at 30 degrees C showed significant cell wall hydrolysing activity. In contrast to the lysis resistance of these bacteria grown at 37 degrees C, mutant cultures grown at 30 degrees C exhibited significant degrees of autolysis when treated with detergent or cell wall inhibitors. Extracts of the mutant cultures contained a cell wall hydrolysing activity that was rapidly inactivated during incubation at 37 degrees C.

Amidohydrolases↗
PubMed1985

Heterologous strain immunity in bovine babesiosis using a culture-derived soluble Babesia bovis immunogen.

The cross-protective capacity of culture-derived soluble immunogens against heterologous Babesia bovis strains from different geographical locations of Latin America was examined. Susceptible yearling cattle were either immunized with immunogens derived from Venezuelan or Mexican strains, or were administered a multi-component immunogen containing antigens of the Australian, Mexican and Venezuelan strains. Cattle were challenged with virulent B. bovis organisms of the Argentinian, Colombian, Ecuadorean, Mexican and Venezuelan strains. The major parameters used to evaluate cross-protection were the following: presence, level and duration of parasitemia; maximal PCV reduction; level and duration of fever; determination of fibrinogen and cryofibrinogen; homologous and heterologous antibody levels; and net gains in body weight. Results showed good protection with a Venezuelan B. bovis immunogen after homologous and heterologous challenge exposures. A low degree of cross-immunity was observed when cattle vaccinated with the Mexican immunogen were challenged with each of the heterologous strains.

Animals↗
PubMed1985

Nutritional deficiencies in institutionalized mentally retarded and physically disabled individuals.

The folic acid, riboflavin, and vitamin A status of 150 individuals in a hospital for mentally retarded persons was examined. Because many of the subjects were incontinent, it was necessary to use blood samples. Folic acid deficiency was determined from plasma levels and from examination of stained peripheral blood smears for megaloblastic changes in the leucocytes. Riboflavin deficiency was determined from estimation of erythrocyte glutathione reductase and vitamin A in plasma by a colorimetric method. Twenty percent of the subjects had evidence of folic acid deficiency, 17% had evidence of riboflavin deficiency, and none had vitamin A deficiency.

Adolescent↗
PubMed1983

Measurements of intracellular ionized calcium in squid giant axons using calcium-selective electrodes.

Ca2+-selective electrodes have been used to measure free intracellular Ca2+ concentrations in squid giant axons. Electrodes made of glass cannulas of about 20 microns in diameter, plugged with a poly(vinyl chloride) gelled sensor were used to impale the axons axially. They showed a Nernstian response to Ca2+ down to about 3 microM in solutions containing 0.3 M K+ and 0.025 M Na+. Sub-Nernstian but useful responses were obtained up to pCa 8. The electrodes showed adequate selectivity to Ca2+ over Mg2+, H+, K+ and Na+. To calibrate them properly, a set of standard solutions were prepared using different Ca2+ buffers (EGTA, HEEDTA, nitrilotriacetic acid) after carefully characterizing their apparent Ca2+ association constants under conditions resembling the axoplasmic environment. In fresh axons incubated in artificial seawater containing 4 mM Ca2+, the mean resting intracellular ionized calcium concentration was 0.106 microM (n = 15). The Ca2+-electrodes were used to investigate effects of different experimental procedures on the [Ca2+]i. The main conclusions are: (i) intact axons can extrude calcium ions at low [Ca2+]i levels by a process independent of external Na+; (ii) poisoned axons can extrude calcium ions at high levels of [Ca2+]i by an external Na+-dependent process. The level of free intracellular Ca attained at these latter conditions is about an order to magnitude greater than the resting physiological value.

Animals↗
PubMed1983

Mechanism of phage-induced lysis in pneumococci.

Earlier studies have suggested the possible role of host autolytic enzyme in the release of progeny phage from Dp-1 infected pneumococci. Several new experiments described here reinforce this notion. Specifically, the resistance of an autolysis-defective mutant to infection at low phage to cell ratios could be eliminated by prior 'coating' of the host bacteria with pneumococcal autolysin isolated from wild-type cells. Similar, productive infection was also possible by lowering the temperature of incubation to 30 degrees C, a condition that leads to a partial activation of the thermosensitive residual autolysin in the mutant cells. Other experiments, however, clearly indicate the role of the newly discovered phage-associated lysin (PAL), reported in the accompanying communication, in bacteriophage release and culture lysis; specifically, lysis was stimulated by reducing agents and inhibited by cardiolipin. It seems that both the host-related and the PAL activities are involved with Dp-1 induced lysis of pneumococci.

Bacteriolysis↗
PubMed1983

A phage-associated murein hydrolase in Streptococcus pneumoniae infected with bacteriophage Dp-1.

A phage-associated murein hydrolase activity capable of degrading pneumococcal cell walls was isolated and purified to homogeneity from the phage-induced lysate of an autolysis-defective pneumococcal mutant infected with the bacteriophage Dp-1. Some properties of the enzyme resembled those of the wild-type (host) pneumococcal murein hydrolase: cell walls prepared from ethanolamine-grown pneumococci were resistant to the enzyme; the activity was inhibited by the Forssman antigen and was sensitive to proteolytic enzymes. The phage-associated enzyme was not inhibited by antiserum prepared against the purified pneumococcal murein hydrolase; the activity was stimulated by reducing agents and was partially inhibited by cardiolipin. The subunit molecular weight of the phage-associated enzyme was somewhat smaller (31 000) than that of the pneumococcal hydrolase (35 000). This appears to be the first description of a phage-associated murein hydrolase activity in pneumococci.

Amidohydrolases↗
PubMed1982

Malignant melanoma with unknown primary site.

From 1955 to 1976, 129 patients were seen with metastatic malignant melanoma from an unknown primary site, comprising 8.1% of all the referred patients with malignant melanoma. Eighty-two percent of the patients presented with a history of mass or lump. Overall median survival and 5-year survival rates after onset of symptoms were 10 months and 13%, respectively. Patients with lesions of the head and neck area had 5-year disease-free survival of 25%, whereas those with lymph node disease had a survival of 18%. Twenty-nine patients with regional disease had wide excision (usually lymphadenectomy) and their 5-year disease-free survival was 58%. Regional disease in patients with malignant melanoma of unknown primary site should be treated with radical surgical excision, since the survival is comparable or better to that of patients with regional disease having known and excised primary site.

Adolescent↗
PubMed1982

The folate in human milk.

In previous studies of the folate content of human milk, samples were prepared for assay by a method that resulted in a turbid solution that was then assayed by a turbidimetric microbiological method. We have used an improved microbiological assay in which the milks were treated with rennin to precipitate casein and heated in a buffered ascorbate to coagulate lactalbumin and lactoglobulin. Milks were obtained serially from nursing mothers for periods ranging from 1 day to 6 months postpartum. The results showed that the folate in human milk has few glutamate residues since treatment with a purified folate conjugase preparation release no additional folate activity for Lactobacillus casei. Colostrum is relatively low in folate, but milk folate increases as lactation proceeds. During each stage of lactation there was great variation in milk folate content among the women. In the case of a folate-deficient woman, supplementation with folic acid resulted in a prompt increase in milk folate level.

Adult↗
PubMed1982

Choline-containing bacteriophage receptors in Streptococcus pneumoniae.

Choline-containing teichoic acid seems to be essential for the adsorption of bacteriophage Dp-1 to pneumococci. This conclusion is based on the following observations: In contrast to pneumococci grown in choline-containing medium, cells grown in medium containing ethanolamine or other submethylated aminoalcohols instead of choline were found to be resistant to infection by Dp-1. Live choline-grown bacteria and heat- or UV-inactivated cells and purified cell walls prepared from these cells were capable of adsorbing phage Dp-1; ethanolamine-grown pneumococci or cell wall preparations were unable to do so. Adsorption of Dp-1 to choline-containing cell walls was competitively inhibited by phosphorylcholine and by several choline-containing soluble cell surface components, such as the Forssman antigen and the teichoic acid-glycan complexes formed by autolytic cell wall degradation. Cell walls prepared from pneumococci grown in ethanolamine or phosphorylethanolamine were inactive. Electron microscopic studies with pneumococci that had segments of choline-containing cell wall material amid ethanolamine-containing regions indicated that the Dp-1 phage particles adsorbed exclusively to the choline-containing surface areas. We suggest that the choline residues of the pneumococcal teichoic acid are essential components of the Dp-1 phage receptors in this bacterium.

Adsorption↗
PubMed1981

Variability of electrocardiographic and enzyme evolution of myocardial infarction in man.

We have studied the time course of development of ST segment elevation, R wave loss, and Q wave development in 41 patients using 35 lead praecordial mapping or 12 lead electrocardiograms in those with anterior and inferior infarcts, respectively. The first recording was at a mean time of six hours after the onset of pain; subsequent records were taken every eight hours for 24 hours, every 12 hours for the second day, and every day thereafter. Serial CK MB estimates were obtained at every four hours for the first 72 hours. There was good agreement in the time course between the electrocardiogram and enzyme evolution. Forty-one per cent of patients showed rapid infarction with R wave and Q wave evolution complete within 12 hours of pain and accompanied by a short duration of enzyme release (mean = 19.30 hours). Fifty-nine per cent of patients showed more prolonged infarction with longer R wave and Q wave evolution and enzyme release (mean = 30 hours). Four patients also showed delayed reinfarction. ST segment elevation was maximal at six hours in the whole group and was significantly lower thereafter. Patients with rapid infarction showed high initial ST segment elevation which decreased promptly compared with those with prolonged infarction, who showed moderate but more persistent ST segment elevation. This study shows the variability in the time course of the electrocardiogram and enzyme evolution after myocardial infarction in man.

Aged↗