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R Lopez

Publications and source records attributed to R Lopez.

At least 37 records · Page 2Linked to original sources
PubMed1991

Analgesia for formalin-induced pain by lateral hypothalamic stimulation.

Few studies of analgesia induced by electrical brain stimulation have examined the effects of brain stimulation on responses to tonic pain stimuli. Recent evidence suggests that analgesia for tonic and phasic pain may involve different neural substrates. The present study examined the effects of lateral hypothalamic (LH) stimulation on responses to tonic pain induced by subcutaneous formalin. Our findings demonstrate that LH stimulation produced analgesia for tonic pain and that the effect is primary and not related to stress-induced analgesia. The results are discussed in relation to hypotheses regarding the different neural substrates involved in analgesia for tonic and phasic pain.

Analgesia↗
PubMed1991

Survival and synapse formation of transplanted rat rods.

Isolated rods enzymatically removed from normal adult rat retina have been transplanted to the subretinal space of adult rats with a retinal dystrophy which has destroyed almost all the photoreceptors. These transplanted rods survive for months after transplantation during which time they form synapses with other retinal cells. Rod spherules with large amounts of synaptic vesicles and synaptic ribbons are found forming discreet contacts with pre- and post-synaptic densities in arrangements closely resembling those seen in the normal retina.

Animals↗
PubMed1991

In vivo glucocorticoid modulation of guinea pig splenic macrophage Fc gamma receptors.

Although glucocorticoids are widely used in the treatment of immunohematologic disease, their relative efficacy is uncertain. We used an animal model, which has helped to elucidate the role of splenic macrophage Fc gamma receptors in the clearance of IgG-coated cells, to investigate whether each Fc gamma receptor is modulated by glucocorticoids to the same extent and to examine the relative potency of three commonly used glucocorticoids. Cortisol, prednisone, and dexamethasone all impaired the clearance of IgG-coated erythrocytes. However, dexamethasone was more effective than either prednisone or cortisol (P less than 0.001). Furthermore, splenic macrophages isolated from glucocorticoid-treated animals expressed impaired Fc gamma receptor function. This effect was greater in macrophages isolated from dexamethasone-treated animals, as compared to either cortisol- or prednisone-treated animals (P less than 0.001). To assess the effect of glucocorticoids on the two types of guinea pig splenic macrophage Fc gamma receptors, Fc gamma R1,2 and Fc gamma R2, specific immunoglobulin isotypes were used to measure macrophage binding of IgG-sensitized erythrocytes. Cortisol and prednisone primarily affected Fc gamma R2, whereas dexamethasone inhibited the function of both guinea pig Fc gamma receptors. Furthermore, dexamethasone was more effective (P less than 0.01) than either prednisone or cortisol in inhibiting the ability of both receptors to bind IgG-sensitized cells. Fluorescence-activated cell sorter analysis and fluorescence microscopy with monoclonal antibodies specific for each of these two receptors demonstrated that essentially all splenic macrophages expressed both receptors, and that these glucocorticoids decreased the level of each Fc gamma receptor protein expressed, rather than altering receptor mobility and clustering in the macrophage membrane. The effect on both Fc gamma receptors was greatest with dexamethasone and least with cortisol. These studies demonstrate the significant role of guinea pig splenic macrophage Fc gamma R2 in immune clearance and in the binding of IgG-coated cells. They demonstrate a differential effect of glucocorticoid hormones on Fc gamma receptor function and on surface receptor protein. Furthermore, they suggest that dexamethasone may be a more effective glucocorticoid than either prednisone or cortisol in inhibiting the clearance of IgG-coated cells by its effect on splenic macrophage Fc gamma receptors.

Animals↗
PubMed1991

Transplanted photoreceptors identified in dystrophic mouse retina by a transgenic reporter gene.

Dissociated photoreceptor cells from a transgenic strain of mice, containing a bovine promoter lac Z gene construct, were transplanted to the dystrophic retinas of a strain of mice (C3H, rd/rd) without obvious photoreceptors. The transgenic photoreceptor cells expressed beta-galactosidase and were distinguishable from the host retinal cells by light and electron microscopy after the 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside histochemical reaction. These results showed that transplanted transgenic photoreceptor cells survived at least 1 month in the host retina and had a primitive outer segment and a well-developed synaptic terminal.

Animals↗
PubMed1991

Transplantation of photoreceptors labeled with tritiated thymidine into RCS rats.

Tritiated thymidine was administered to newborn rats to label photoreceptors, about 50% of which are still dividing. These photoreceptors were enzymatically dissociated and separated from the remainder of the retina after the infant rat matured. These labeled photoreceptors were then transplanted into a foreign host retina in the region of the outer nuclear layer. The hosts were ocular, albinotic, Royal College of Surgeons (RCS) rats, congenic to the normal donors and at least 4 months old, a time when virtually all the photoreceptors have degenerated from their retinas. The transplant site was examined at various times after transplantation by light microscope autoradiography. Labeled photoreceptor cell bodies were found in clusters in the outer nuclear layer region for as long as 3 months after transplantation surgery.

Animals↗
PubMed1990

Evidence for conformers of rabbit muscle adenylate kinase.

Changes of the apparent Mr values and the circular dichroism patterns suggest the existence of three relatively stable conformers of rabbit muscle adenylate kinase (RMAK). The effects of dithiothreitol (DTT) which stimulates activity, pH, the substrates, and ATP on the Mr value and the Stokes radius of RMAK were determined from gel filtration data, and apparent Mr values near 22,000, 26,000, and 29,000 resulted. Substrates generated multiple Mr values, suggesting the presence of multiple conformers of RMAK. The higher apparent Mr values were obtained in the presence of DTT and at the higher substrate concentrations, indicating more open conformations. The effect of the substrates on the conformation of RMAK is discussed in relation to the kinetic mechanism of this random bireactant system. Circular dichroism studies were undertaken in order to observe any changes in the secondary structures of RMAK in relation to changes of the Mr values. The secondary structure composition of RMAK, determined under our conditions, does not agree with results determined from crystallographic studies. The gel filtration and the CD studies suggest that above pH 7 a more open conformation of RMAK obtains in the presence of DTT. The results of these studies are discussed with reference to the location of the active sites.

Adenylate Kinase↗
PubMed1990

Long term evaluation of high tibial valgus osteotomy.

We present a long term evaluation of 100 high valgus tibial osteotomies with a mean follow up of 11 years. Knees with slight or moderate osteoarthritis had the best results. Slight overcorrection was beneficial, but gross overcorrection was not. There were few complications and the overall long term results were good.

Activities of Daily Living↗
PubMed1990

Problems in diagnosis and management of desmoid tumors.

Thirty-two primary desmoid tumors occurred in 29 patients. The median patient age was 32 years, and 55% of the patients were females. An antecedent history of trauma at the tumor site was elicited from 28% of patients. Thirty-one of 32 primary tumors were completely excised at initial presentation. Five tumors were treated with adjuvant radiotherapy. The overall recurrence rate for primary and recurrent lesions was 60%. The recurrence rate in children (88%) was more than twice that found in adults (38%). A single recurrence did not significantly increase the likelihood of a subsequent recurrence. Greater than 90% of all recurrences took place within 3 years of treatment. The rate of recurrence was not clearly influenced by the status of histologic margins, although this was examined in less than half the tumors. Desmoid tumors are aggressive neoplasms that exhibit a strong propensity for local recurrence. They should be treated as low-grade malignancies with documentation of histologic margins and close clinical follow-up within the framework of a tumor registry.

Abdominal Muscles↗
PubMed1990

Purification of adenosine deaminase from chicken-egg yolk by affinity column chromatography.

Adenosine deaminase (adenosine aminohydrolase; E.C. 3.5.4.4) has been purified 4686-fold from egg yolk. The procedure developed was used to isolate the enzyme from eight chicken eggs. An easily prepared affinity column employing purine riboside was used as the final step in the purification. The method developed permits the rapid isolation and a high recovery of the protein. The specific activity of the enzyme preparation obtained is 81.4 mU/mg.

Adenosine Deaminase↗
PubMed1990

Sequence of the Streptococcus pneumoniae bacteriophage HB-3 amidase reveals high homology with the major host autolysin.

We have sequenced a DNA fragment containing the pneumococcal bacteriophage HB-3 hbl gene, which codes for the phage lytic amidase. A remarkable nucleotide similarity (87.1%) between the lytA gene, coding for the pneumococcal amidase, the major autolysin of Streptococcus pneumoniae, and the hbl gene was found. This similarity completely disappeared outside the open reading frames coding for both amidases. The hbl gene transformed amidase-deficient strains of S. pneumoniae to the wild-type phenotype, and Southern blotting experiments provided evidence for recombination between donor and recipient genes. A comprehensive evaluation of these and previous results on the peptidoglycan hydrolases of S. pneumoniae and its bacteriophages suggested that recombination mechanisms participate in the evolution of the genes coding for these enzymes.

Amidohydrolases↗
PubMed1990

Characterization of the pneumococcal bacteriophage HB-3 amidase: cloning and expression in Escherichia coli.

HB-3, a temperate bacteriophage of Streptococcus pneumoniae, synthesizes its own murein hydrolase activity when multiplying on cultures of pneumococcus. The enzyme (HBL) was purified and biochemically characterized as an N-acetylmuramoyl-L-alanine amidase of 36,000 daltons, and a 2.1-kilobase DraI fragment containing the lysin gene (hbl) was cloned and expressed in Escherichia coli. Our results demonstrated that the primary product of the hbl gene is a form with low enzyme activity that can be converted to a more active form under conditions similar to those previously described for the major pneumococcal autolysin (E. García, J.L. García, C. Ronda, P. García, and R. López, Mol. Gen. Genet. 201:225-230, 1985). The phage-encoded amidase requires the presence of choline in the teichoic acids of the pneumococcal cell walls for in vivo and in vitro activity. Comparative biochemical and immunological tests of the phage-encoded and host amidases revealed a remarkable similarity between these enzymes, although analyses of their N-terminal amino acid sequences allowed us to conclude that the amidases are similar but not identical. This appears to be the first description of the cloning of a phage-encoded amidase in gram-positive bacteria.

Amidohydrolases↗
PubMed1990

Temperate bacteriophages of Streptococcus pneumoniae that contain protein covalently linked to the 5' ends of their DNA.

We have characterized three temperate bacteriophages of pneumococcus (HB-3, HB-623, and HB-746). Although all the phages belong to the same family, the polypeptide composition of the virions and the DNA restriction endonuclease analysis of their DNAs revealed differences among the three phages. The genomes of these bacteriophages have been isolated as DNA-protein complexes. The protein is specifically associated with the two 5' termini of the DNA as shown by experiments carried out with exonucleases. The protein bound to the DNA in the three phages studied, iodinated in vitro with 125I, has a molecular weight of 23,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Treatment of the complexes with chaotropic agents suggested that the protein is covalently bound to the 5' termini of the DNA. Comparative pulsed-field gel electrophoresis analysis and Southern hybridization of the SmaI restriction fragments of DNAs from one lysogenic bacteria and its parental strain revealed that the prophage genome was integrated in the host chromosome.

Bacteriophages↗
PubMed1989

Influence of cardioprotective cyclooxygenase and lipoxygenase inhibitors on peroxidative injury to myocardial-membrane phospholipid.

Oxygenase-catalyzed and non-enzymatic polyunsaturated fatty acid peroxidations have potential pathogenic roles in ischemic-reperfusion damage to the myocardium. Certain oxygenase inhibitors protect heart muscle from irreversible ischemic injury, and some antiperoxidants can inhibit oxygenase enzymes. We investigated the antiperoxidative abilities of eight anti-ischemic, cardioprotective oxygenase inhibitors to prevent myocardial-membrane phospholipid peroxidation through superoxide-driven, iron-promoted reactions with xanthine oxidase as the source of superoxide. Flurbiprofen, ibuprofen, and REV-5901-5 did not affect peroxidation at concentrations up to 1000 microM. BW755C, AA-861, nafazatrom, dipyridamole, and propyl gallate did protect and cardiac lipids against oxidative injury in a concentration-dependent manner with respective and antiperoxidant IC50 values (concentrations at which peroxidation was inhibited by 50%) of 0.22, 1.25, 3.0, 3.6 and 50 microM. Catechin and phenidone, known oxygenase inhibitors not yet evaluated as anti-ischemic agents, were also found to be antiperoxidants at low micromolar concentrations. Four cyclooxygenase inhibitors ineffective against myocardial infarction (aspirin, indomethacin, naproxen, and sulfinpyrazone) evidenced no antiperoxidant properties at concentrations up to 500 microM. The oxygenase inhibitor-antiperoxidants identified could neither quench superoxide radical nor inhibit xanthine oxidase. However, they were able to interrupt the propagation of an on-going peroxidation reaction. Their antiperoxidant profiles resembled those of known antioxidants, such as alpha-tocopherol, which inhibit peroxidation by intercepting lipid free-radical intermediates. These data raise the possibility that at least some oxygenase inhibitors could exert cardioprotective effects by directly influencing the sensitivity of myocardial-membrane phospholipid to peroxidative injury. Consequently, recognition of the antiperoxidant properties of these agents may aid dissection of their physiological and pharmacological actions.

Aspirin↗
PubMed1989

Catroxobin, a weakly thrombin-like enzyme from the venom of Crotalus atrox. NH2-terminal and active site amino acid sequences.

Two thrombin-like isoenzymes, termed catroxobins, were purified by gel filtration and ion exchange chromatography to electrophoretic homogeneity from the venom of the Western diamondback rattlesnake, Crotalus atrox. By SDS-polyacrylamide gel electrophoresis their molecular weights were estimated to be 25,000 and 26,200. A 43-residue NH2-terminal sequence, containing the active histidine residue, was the same for the two isoenzymes. In addition, a 33-residue internal peptide from catroxobin I contained a normal active serine sequence. These sequences were highly homologous to other thrombin-like venom enzymes, and to pancreatic kallikrein and trypsin, but less so to the B chain of thrombin. Catroxobin, possessing 89 TAME esterase units/mg of protein, clotted human fibrinogen very slowly, releasing fibrinopeptide A and a small amount of fibrinopeptide B. No other evidence of cleavage of the fibrinogen molecule was revealed by polyacrylamide gel electrophoresis or HPLC.

Amino Acid Sequence↗