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Biomedical subjects

R Lopez

Publications and source records attributed to R Lopez.

At least 145 records · Page 8Linked to original sources
PubMed1989

Propranolol as xanthine oxidase inhibitor: implications for antioxidant activity.

Propranolol is the beta-blocker most widely used in the management of cardiovascular disorders. It has been proposed that propranolol may act as a "chain-breaking" antioxidant. We have directly examined the ability of propranolol to inhibit superoxide-dependent, iron-promoted cardiac membrane phospholipid peroxidation, with xanthine oxidase (XOD) as a physiologically-recognized, enzymatic superoxide generator. Our results demonstrate that propranolol not only protects cardiac-membrane lipid from peroxidative damage, but also acts as a simple, reversible XOD inhibitor, noncompetitive with xanthine substrate. Propranolol, at effective antiperoxidant and XOD-inhibitory concentrations, cannot scavenge superoxide radical. The antiperoxidative profile of propranolol resembles that of the known XOD inhibitor allopurinol, although allopurinol, a tight-binding substrate-analog competitive with xanthine, inhibits XOD in a manner mechanistically very different from that of propranolol. Furthermore, the antiperoxidative profiles of both propranolol and allopurinol do not resemble those of chain-breaking antioxidants such as alpha-tocopherol. These data, along with the tendency of propranolol to concentrate in myocardial membranes and cytosol, suggest that the observed antioxidant action of propranolol, as a consequence of XOD inhibition, could play a pharmacologic role in propranolol's cardioprotective effects.

Allopurinol↗
PubMed1989

Tacaribe virus L gene encodes a protein of 2210 amino acid residues.

The nucleotide sequence of Tacaribe virus (TV) L gene was obtained from two sets of overlapping cDNA clones constructed by walking along the virus L RNA using two successive synthetic DNA primers. Analysis of the sequence indicated the existence of a unique long open reading frame in the viral complementary strand. The first in-phase AUG codon is in positions 31-33 from the 5' end of the viral complementary L RNA surrounded by a sequence favorable for initiation of protein synthesis. The open reading frame ends at positions 6661-6663. The predicted TV L protein is a 2210 amino acid long polypeptide with an estimated molecular weight of 251,942. Comparison of the amino acid sequence of TV L protein with peptide sequences predicted from L-derived cDNA clones of lymphocytic choriomeningitis virus shows an overall 42% of homology.

Amino Acid Sequence↗
PubMed1989

Transplanted retinal pigment epithelium modifies the retinal degeneration in the RCS rat.

Transplantation of dissociated retinal epithelial cells obtained from the retinas of normal, congenic pigmented strain of rats to Bruch's membrane and the subretinal space of dystrophic rats from the Royal College of Surgeon (RCS) strain can prevent photoreceptor cell degeneration in this retina for at least 4 months after transplantation. Host and transplant cells form close apposition with one another but can be distinguished by the presence of both phagosomes and melanin granules in the transplant and the absence of these inclusions in the host retinal epithelium. Transplanted cells show excessive amounts of phagosomal material within 48 hr after transplantation, implying that restoration of phagocytosis is responsible for the photoreceptor survival.

Animals↗
PubMed1988

Protection of cardiac membrane phospholipid against oxidative injury by calcium antagonists.

Calcium antagonists representative of the four major chemical classes were assessed for their abilities to prevent peroxidation of rat heart membrane lipids through xanthine oxidase-dependent, superoxide-driven, iron-promoted oxygen radical chemistry. The dihydropyridines nifedipine and nitrendipine did not affect peroxidation, even at a concentration (500 microM) approaching their solubility limit. The benzothiazepine diltiazem did protect the cardiac lipids against oxidative injury, but at high micromolar concentrations: 50% inhibition of peroxidation (antiperoxidant IC50) required 510 microM diltiazem. The phenylalkylamines verapamil and gallopamil (D-600) were likewise weak antiperoxidants (approximately 35% inhibition of peroxidation at 500 microM). In contrast, two other alkylamines, bepridil and prenylamine, were very effective membrane lipid protectants with respective antiperoxidant IC50 values of 55 and 75 microM. The diphenylpiperazines flunarizine (IC50 = 190 microM) and cinnarizine (IC50 = 180 microM) displayed moderate antiperoxidant activity. No Ca2+ antagonist inhibited xanthine oxidase under conditions whereby 10 microM allopurinol inhibited enzyme activity by 50%. The effects of the Ca2+ antagonist-antiperoxidants on the kinetics of cardiac membrane lipid peroxidation indicate that they inhibit peroxidation by intercepting oxy- and/or lipid free radical intermediates. These data raise the possibility that antiperoxidant action may contribute to the spectrum of pharmacologic and therapeutic activities of certain Ca2+ antagonists.

Animals↗
PubMed1988

The effect of a high fat diet on the incidence of colonic cancer after cholecystectomy in mice.

An experimental study was designed to evaluate the effects of both a high fat diet and a cholecystectomy on the incidence of carcinogen-induced colon cancer in mice. Sixty pink-eyed jax (P/J) mice were divided equally into two groups. One group was fed a standard rodent diet and the other group received a diet supplemented with 20% corn oil. From each diet group, 50% of the mice had a cholecystectomy and the other 50% had a sham operation. Two weeks after surgery, each mouse received weekly subcutaneous injections of a carcinogen (dimethylhydrazine, 20 mg/kg) for 12 weeks. After the treatment period, the mice were killed and their large bowels were examined. Evaluation of the results demonstrated that the mice that had a cholecystectomy and a high fat diet had the highest incidence (P less than 0.05) of colonic adenocarcinomas.

Adenocarcinoma↗
PubMed1988

Structural requirements of choline derivatives for 'conversion' of pneumococcal amidase. A new single-step procedure for purification of this autolysin.

Tertiary amines appear to be the minimal structure needed to convert in vitro the inactive form (E-form) of pneumococcal amidase to the catalytic active form (C-form). Diethylethanolamine was one of the compounds that converted the E-form, a finding that has been used successfully to develop an affinity chromatography system in DEAE-cellulose for the rapid and efficient purification of lytic enzymes of pneumococcus and its bacteriophages.

Amidohydrolases↗
PubMed1988

Retinoschisis associated with optic nerve pits.

Stereoscopic transparencies studied with magnification and projection suggest that the retinal elevation that communicates with optic pits is frequently a schisislike separation of the internal layers of retina. Thirteen of 15 eyes with optic pits and maculopathy fit the schisis pattern. Separation of the outer layers of the retina is a secondary phenomenon that starts in the macula.

Adult↗
PubMed1988

Radiotherapy and L-triiodothyronine in the treatment of high-grade astrocytoma.

From January 1983 to March 1984, eight patients with high-grade astrocytoma received postoperative irradiation concomitantly with triiodothyronine at the Radiation Therapy Department of the I. González Martínez Oncologic Hospital in San Juan, Puerto Rico. There were no complications related to treatment. One patient is alive without evidence of disease at 39 months and seven patients died with disease, one of whom lived for 3 yr. The survival curve for these patients is similar to the survival curve of 18 patients treated at the University of Chicago by surgery, radiation, and triiodothyronine. The value of triiodothyronine as an adjuvant in the treatment of high grade astrocytoma should be further investigated.

Adult↗
PubMed1988

The effect of increased intracranial pressure (ICP) on gastric motility.

This study evaluates the effect of increased intracranial pressure (ICP) on gastric motility. Nine male cats (weight, 4.84 +/- 1.16 kg) were anesthetized with ketamine and underwent laparotomy for placement of bipolar (silver-silver chloride) electrodes on the serosal surface of the gastroesophageal junction (GEJ), antrum, and prepyloric areas of the stomach. At 1 week frontoparietal burr holes were performed with placement of an epidural Fogarty catheter. Migrating myoelectric complexes (MMCs) were evaluated at the GEJ, antrum, and prepyloric areas at varying levels of ICP (baseline and 20, 40, and 60 mm Hg) using balloon inflation. MMCs at the GEJ were triphasic with a period of 4 sec (+/- 1 sec) at baseline levels. At ICP levels above baseline, periodicity and waveforms at the GEJ became irregular. Waveforms became multiphasic with 1- to 2-sec periods and variable amplitudes. In the antral and prepyloric areas, duration and amplitude of the triphasic MMCs was unchanged from baseline. At 60 mm Hg ICP periodicity was significantly altered at both 1 and 2 weeks. MMCs returned to baseline levels with balloon deflation. The data indicate that elevated ICP (to 60 mm Hg) results in consistent and reproducible alterations of MMC periodicity, suggesting that such alterations may influence gastric motility.

Animals↗
PubMed1988

The stability of pH, PCO2, and calculated [HCO3] of urine samples collected under oil.

In order to determine the stability of directly measured pH and PCO2, and calculated [HCO3] in stored urine, 11 alkali-loaded normal subjects provided 33 spot and sixteen 24-hour mineral oil-covered, thymol-preserved, refrigerated urine samples. For the spot samples, pH and PCO2 were measured immediately and again at 4 and 24 h. In addition, immediately after voiding, 24 of the spot samples were split into oil-covered and no-oil moieties and analyzed immediately and again at 4 and 24 h. pH and PCO2 measurements of the 24-hour collections were carried out immediately after completion and again 24 h later. The results demonstrated the importance of using oil to limit the escape of CO2 from stored urine. Thus, after 24 h the oil-uncovered subgroup of 24 spot urine samples sustained a 82% decline in PCO2 and 20% fall in [HCO3]. In contrast, the corresponding percentage decrements in the oil-covered samples were 16 and 1%, respectively. The results also indicated that even with oil there is loss of CO2, which increases with time and which shows a statistically significant direct correlation with the baseline level of PCO2. Nevertheless, modest loss of CO2 usually produces only slight decrements in [HCO3] because of the countervailing influence of the resultant increase in pH. We conclude that the use of mineral oil is necessary in order to obtain adequate stability of PCO2, pH and [HCO3] in refrigerated urine requiring several hours or more of storage.

Bicarbonates↗
PubMed1987

Bovine babesiosis: induction of protective immunity with culture-derived Babesia bovis and Babesia bigemina immunogens.

The comparative protective efficacy of culture-derived Babesia bovis and B. bigemina immunogens against challenge exposure of susceptible crossbred cattle to heterologous strains was examined and correlated with the antigenic threshold requirements for induction of protective immunity. Strong protection was observed in animals vaccinated with 10 ml-equivalent doses of soluble, B. bovis exoantigen-containing supernatant fluids. Similar protective responses to B. bigemina exoantigens were evident even at 1 ml-equivalent dosages. In addition, the efficacy of a combined B. bovis-B. bigemina immunogen was assessed with a dose-response analysis in highly susceptible, purebred cattle. Vaccinated animals were protected against clinical babesiosis, and significant weight gains were recorded after challenge infection with virulent parasites.

Animals↗
PubMed1987

Gallstone pancreatitis in adolescents.

During a 5-year period (1980 to 1985) in the Adolescent Unit at Bronx-Lebanon Hospital Center, 18 patients were admitted with the diagnosis of gallstone disease, four of whom, at the time of their admission, had associated acute pancreatitis. Although gallstone pancreatitis is infrequent in adolescents, it is an important differential diagnosis of upper abdominal pain in youngsters with gallstone disease. The most frequently encountered mechanisms of gallstone pancreatitis in adolescents appear to be impacted stones, congenital pathology in the ampullary area, and passage of small stones through the common bile duct, with temporary obstruction and inflammation followed by disruption of pancreatic ductules and/or acinar cell membrane. Proper management includes cholecystectomy and the mandatory performance of an intraoperative cholangiogram. Sphincterotomy or sphincteroplasty, which are frequently performed in adults with gallstone pancreatitis, should be avoided in adolescents. Even if impacted stones have to be removed at this age, papillotomy suffices. After an acute episode, a properly timed surgical treatment is curative.

Acute Disease↗