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Biomedical subjects

R Rodriguez

Publications and source records attributed to R Rodriguez.

At least 19 recordsLinked to original sources
PubMed1992

Capillary electrophoresis of hemoglobins and globin chains.

Capillary isoelectric focusing (cIEF) and free zone capillary electrophoresis were evaluated for separation of native hemoglobins and globin chains. High-resolution separations of adult human hemoglobin A, fetal human hemoglobin F, and hemoglobin variants S and C were obtained using cIEF with cathodic mobilization. Absorbance detection in the UV and visible regions were compared, and on-line fast UV or visible-wavelength scanning detection was used to obtain spectral information on separated components. Globin chain analysis was performed on the same hemoglobin species by free zone capillary electrophoresis following precipitation of the protein with acidic acetone. Free zone separations were carried out at low pH in the presence of 7 M urea.

Electrophoresis↗
PubMed1992

A method for determination of N-glycosylation sites in glycoproteins by collision-induced dissociation analysis in fast atom bombardment mass spectrometry: identification of the positions of carbohydrate-linked asparagine in recombinant alpha-amylase by treatment with peptide-N-glycosidase F in 18O-labeled water.

Previously, a combined use of fast atom bombardment (FAB) mass spectrometry and peptide N-glycosidase F, an enzyme that cleaves the beta-aspartylglycosylamine linkage of Asn-linked carbohydrates, was successfully applied to identification of N-glycosylation sites in a glycoprotein with the known or DNA-derived sequence (S. A. Carr and G. D. Roberts, 1986, Anal. Biochem. 157, 396-406). Here, we extended the method for easier identification of N-glycosylation sites in a glycoprotein even with unknown sequence. The glycoprotein is digested with peptide-N-glycosidase F in buffer containing 40 at% H2 18O, to yield a deglycosylated protein whose carbohydrate-linked Asn residues are converted to Asp partly labeled with 18O at their beta-carboxyl group during this digestion. The deglycosylated protein is further digested with proteolytic enzymes in an appropriate buffer prepared with normal water, and then peptides are separated on a reversed-phase column by HPLC. Peptides in which carbohydrate-linked Asn has been converted to Asp show a pair of signals ([M + 1]+ and [M + 3]+) in FAB mass spectra due to the partial incorporation of 18O into the beta-carboxyl groups of Asp residues, while the other peptides show normal isotopic ion distributions. Thus, both formally N-glycosylated peptides and, using collision-induced dissociation analysis, N-glycosylation sites can be identified. The application of the present method to the determination of N-glycosylation sites in a recombinant glycoprotein, Bacillus licheniformis alpha-amylase, is described.

Amidohydrolases↗
PubMed1992

Effect of depolarizing agents on the Ca(2+)-independent and Ca(2+)-dependent release of [3H]GABA from sheep brain synaptosomes.

The purpose of the present study was to compare the effects of several depolarizing agents on both the membrane potential and on the release of [3H] gamma-aminobutyric acid (GABA) from sheep brain cortex synaptosomes. We examined the effects of KCl, 4-aminopyridine (4-AP), veratridine, ouabain and tetraphenylphosphonium cation (TPP+) on Ca(2+)-independent (carrier-mediated) and Ca(2+)-dependent (exocytotic) release. We found that, in the absence of Ca2+, KCl at 40 mM releases 7.57 +/- 0.65%, veratridine at 50 microM releases 45.85 +/- 2.48%, ouabain at 1 mM releases 8.62 +/- 0.93% and TPP+ at 1 mM releases 4.09 +/- 0.37% of the total accumulated neurotransmitter, provided that the external medium contains Na+. These are about the maximal values of release obtained with each depolarizing agent in a Na+ medium and in the absence of Ca2+. Replacing external Na+ with choline blocks the release observed in the presence of the depolarizing agents in the absence of Ca2+, and this divalent ion can increase [3H]GABA release only for K+ or 4-AP. Synaptosomal depolarization requires Na+ except for K+ depolarization. Furthermore, although Ca2+ stimulates the release of [3H]GABA due to K+ depolarization (13.56 +/- 0.44%) or due to 4-AP (4.26 +/- 0.51%), it inhibits the release due to the other depolarizing agents. The amount of [3H]GABA released by 4-AP in Na+ medium (4.26 +/- 0.51%) is similar to that induced by KCl in the presence of Ca2+ in the absence of Na+ (3.39 +/- 0.29%) which represents only exocytotic release. This suggests that the Ca(2+)-dependent exocytotic release of [3H]GABA can be specifically induced by 4-AP in a Na+ medium, or by KCl in the absence of Na+, as reported by us earlier. The observation that Ca2+ inhibits the Ca(2+)-independent release is of interest because it suggests that Ca2+ may modulate the release of cytoplasmic GABA probably by inhibiting the carrier-mediated release of GABA. It is of interest as to whether Ca2+ regulation depends on intracellular Ca2+.

4-Aminopyridine↗
PubMed1992

Effect of various psychotropic drugs on the performance of avoidance and escape behaviors in rats.

The effect of different doses of nine psychotropic drugs upon conditioned avoidance responses (CARs) developed on a stable basis, after appropriate training, was investigated in rats and compared with their capacity to disrupt escape responses (ERs). Haloperidol (HAL), chlorpromazine (CPZ), morphine (MOR), pentobarbital (PENT), chlordiazepoxide (CDP), meprobamate (MPB), and amphetamine (AMPH) dose dependently inhibited both behaviors. Imipramine also disrupted CARs dose dependently, but did not affect ERs at maximal tolerated doses. Significant differences in the minimal effective doses, effective dose range, and time of onset and duration of action, as well as in potency, were observed. The quantitative determination of the level of selectivity, based upon the ratio ED50 escape failure/ED50 avoidance failure, indicated that all CNS depressants tested caused a selective inhibition of avoidance behavior. HAL was found to be the most specific, followed, in order, by CDP, MOR, CPZ, MPB, and PENT, whose ratio values were not significantly different. AMPH produced a nearly parallel impairment of both behaviors and quipazine only affected CARs at toxic doses. It is concluded that both neuroleptic and nonneuroleptic CNS depressant drugs have selective inhibitory effects on avoidance behavior. Data revealed differences that were more quantitative than qualitative.

Animals↗
PubMed1992

Are mitotic index and lymphocyte proliferation kinetics reproducible endpoints in genetic toxicology testing?

Lymphocyte proliferation kinetics is an endpoint used in genetic toxicology which has recently been proposed as an alternative for the screening of new cytostatic drugs. Although great variability for this parameter has been reported, there are few reports about the intra- and inter-individual variation of the effects of chemicals on this endpoint. For this reason, experiments were conducted to evaluate the reproducibility of the effects of a well-known cytostatic, mitomycin C (MMC), on the proliferation of PHA-stimulated human lymphocytes, both over time and among samples from several donors. Although inter-individual variability was shown in both parameters in untreated and treated cultures, this variation was not significant. Intra-individual variation was significantly detected only in cultures treated with 0.1 microM MMC.

Adult↗
PubMed1992

Optimism, coping, psychological distress, and high-risk sexual behavior among men at risk for acquired immunodeficiency syndrome (AIDS).

In a cohort of gay men responding to the threat of acquired immunodeficiency syndrome (AIDS), dispositional optimism was associated with less distress, less avoidant coping, positive attitudes as a coping strategy, and fewer AIDS-related concerns. Men who knew they were seropositive for human immunodeficiency virus (HIV) were significantly more optimistic about not developing AIDS than men who knew they were seronegative for HIV. This AIDS-specific optimism was related to higher perceived control over AIDS and to active coping among seropositive men only and to health behaviors in both serostatus groups. There was no relation of optimism to risk-related sexual behavior. It is concluded that optimism is psychologically adaptive without necessarily compromising health behavior. It is also concluded that it is useful to distinguish between event-based optimistic expectations and dispositional optimism.

AIDS Serodiagnosis↗
PubMed1992

Control of neck nodes in squamous cell carcinoma of the head and neck by radiotherapy: prognostic factors.

313 patients with cervical metastases from a squamous carcinoma of the head and neck treated with radiotherapy, were studied by means of a multivariant analysis in order to determine the prognostic factors for cure. These were: lymph node response to irradiation (P = 0.0000), size of node (P = 0.0000), radiotherapy dose (P = 0.0037), condition of the primary (controlled vs non-controlled) (P = 0.0015), recurrent cervical metastases post-surgery (P = 0.0286).

Adolescent↗
PubMed1992

Development and validation of prognostic models in metastatic breast cancer: a GOCS study.

The significance of several prognostic factors and the magnitude of their influence on response rate and survival were assessed by means of uni- and multivariate analyses in 362 patients with stage IV (UICC) breast carcinoma receiving combination chemotherapy as first systemic treatment over an 8-year period. Univariate analyses identified performance status and prior adjuvant radiotherapy as predictors of objective regression (OR), whereas the performance status, prior chemotherapy and radiotherapy (adjuvants), white blood cells count, SGOT and SGPT levels, and metastatic pattern were significantly correlated to survival. In multivariate analyses favorable characteristics associated to OR were prior adjuvant radiotherapy, no prior chemotherapy and postmenopausal status. Regarding survival, the performance status and visceral involvement were selected by the Cox model. The predictive accuracy of the logistic and the proportional hazards models was retrospectively tested in the training sample, and prospectively in a new population of 126 patients also receiving combined chemotherapy as first treatment for metastatic breast cancer. A certain overfitting to data in the training sample was observed with the regression model for response. However, the discriminative ability of the Cox model for survival was clearly confirmed.

Analysis of Variance↗
PubMed1992

In vitro spontaneous synthesis of beta 2-microglobulin amyloid fibrils in peripheral blood mononuclear cell culture.

beta 2-microglobulin-related amyloidosis (A beta 2M), in long-term dialysis patients, is a new and frequent complication for which the pathogenesis remains unknown. The authors documented, by light and high resolution electron microscopy, the spontaneous polymerization of beta 2-microglobulin to amyloid fibrils in mononuclear cell culture supernatants from dialysis patients. These data provide significant information about the pathogenesis of dialysis-amyloidosis, revealing an unusual and different fibrillogenic mechanism for beta 2-microglobulin and dialysis-amyloidosis than for other forms of amyloidosis. beta 2-microglobulin does not appear to require a proteolytic process before polymerization into amyloid fibrils and deposits. This study represents the first cell culture system in which beta 2-microglobulin amyloid fibrils have been spontaneously created.

Amyloid↗
PubMed1991

Characterization and localization of Plasmodium falciparum surface antigens on infected erythrocytes from west African patients.

The malaria-induced surface antigens on Plasmodium falciparum-infected erythrocytes from West African patients were characterized by agglutination of infected cells by human sera, surface immunofluorescence of live infected cells, inhibition of cytoadherence to C32 melanoma cells by human sera, immunoelectron microscopy (immunoEM), and immunoprecipitation. In a nonimmune individual, serum antibody reactivity to surface antigens of infected cells was acquired during convalescence, as tested by all five methods, and was generally parasite isolate-specific. By contrast, adult hyperimmune West African sera reacted with many isolates, including isolates from geographically distinct regions. A quantitative correlation was established between agglutination and surface immunofluorescence assay titers, and between surface immunofluorescence assay and immunoEM reactivity, suggesting that a single antigen or a set of coexpressed antigens is being detected. Surface iodination of infected cells identified trypsin-sensitive high M, antigens in the sodium dodecyl sulfate extract. All sera tested that agglutinated infected cells also immunoprecipitated these antigens. The same surface antigens were immunoprecipitated by the homologous convalescent serum as by adult sera. By immunoEM these antigens were localized exclusively at the knob-like protrusions of infected cells, where they may participate in adherence to vascular endothelium.

Africa, Western↗
PubMed1991

A comparative study of histamine and K+ effects on (Ca(2+)-Mg2+)-ATPase activity in synaptosomes.

Histamine (10(-4) M) and 60 mM K+, but not 60 mM Na+ or 60 mM choline+, increased the maximal synaptosomal (Ca(2+)-Mg2+)-ATPase activity by 15 and 36% respectively and decreased the extrasynaptosomal Ca2+ concentration necessary to reach it. Histamine and K+ enhanced the synaptosomal (Ca(2+)-Mg2+)-ATPase activity in a concentration-dependent manner. In synaptic plasma membranes histamine (10(-4) M) and 60 mM choline+ were not able to alter the enzymatic activity, however 60 mM K+ and 60 mM Na+ elevated (Ca(2+)-Mg2+)-ATPase activity by 20 and 15%, respectively, without altering the affinity for Ca2+. Histamine effects in synaptosomes were mediated by H2 receptor stimulation. 3-Isobutyl-1-methyl-xanthine (10(-4) M) potentiated (15%) the maximal histamine effect. The slow Ca2+ channel antagonists verapamil and diltiazem, both at 10(-6) M, completely inhibited K+ effects in synaptosomes, however histamine effects were only blocked by verapamil. The data suggest that K+ and histamine effects on synaptosomal (Ca(2+)-Mg2+)-ATPase activity are mediated by increases of intrasynaptosomal Ca2+ levels. Moreover, histamine effects on synaptosomal enzyme activity were mediated by cAMP.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Antigen shedding vs. development of natural suppressor cells as mechanism of tumor escape in mice bearing Ehrlich tumor.

C57BL/6J mice immunized with devitalized Ehrlich tumor (ET) cells produce high serum levels of IgM antibodies to ET cell-surface carbohydrates that are critical in the observed resistance against this tumor. However, this response is not found in ET-bearing mice at any stage of tumor development. Since previous studies had shown splenic natural suppressor (NS) cells in ET-bearers, their role in such IgM impairment was assessed. Here we show that tumor-bearers' spleen cells (TBSC) are unable to produce IgM in vitro in response to LPS, due to the presence of NS cells. Nevertheless, TBSC do produce IgM antibodies to ET cell-surface carbohydrates in increasing amounts as the tumor progresses. Yet these antibodies are not detected in sera of ET-bearers and are greatly decreased in immunized mice with a growing tumor. Moreover, increasing amounts of circulating carbohydrates, able to absorb most specific IgM, are found in ET-bearing sera associated with a large molecular size structure(s). These carbohydrates are also found in ET cell-culture supernatants and cell-free ascites fluid derived from this tumor, indicating their tumor origin. Taken together, our results indicate that lack of specific IgM antibodies in ET-bearing mice is not due to faulty production, but to in vivo absorption by carbohydrates shed from ET cells in increasing amounts as the tumor progresses. Thus, NS cells are unable to suppress this IgM production in vivo, despite the strong suppressor activity they show for many responses in vitro.

Animals↗
PubMed1991

Reversal of neuromuscular blockade in humans by neostigmine and edrophonium: a mathematical model.

Generalizations of the integrated model describing the interaction of nondepolarizing neuromuscular blocking drugs with reversible anticholinesterase drugs described in Unadkat et al. (1) are reported. The models can deal with possible incomplete reversal (irreversible block) and/or noninstantaneous anticholinesterase kinetics. Experimental data were obtained from 22 human volunteers. Different levels of steady-state vecuronium block were induced in each volunteer (in the range of 50% to 95%), and reversed by short infusions of edrophonium (10 volunteers) or neostigmine (12 volunteers). Edrophonium or neostigmine concentrations and twitch tension (measured as the force of thumb adduction) were measured. The generalized integrated models fit the data well. In the case of neostigmine we find a nondistributional delay in its action. We relate this delay to the slow decarbamylation rate of the (neostigmine-induced) carbamylated anticholinesterase observed in vitro, and are able to model such noninstantaneous anticholinesterase kinetic processes. For both edrophonium and neostigmine we detect an inverse relationship between the (induced) level of initial block and maximal percentage recovery.

Adult↗
PubMed1991

Amelioration of renal ischemic injury by phosphocreatine.

Phosphocreatine (PCr) is a critical intracellular energy reservoir used in the regeneration of ATP. The aim of this study was to determine the efficacy of exogenously added PCr on preservation of renal function in an in vitro model. The renal artery and ureter of a rat were cannulated and the kidney was subjected to 45 min of normothermic in vivo ischemia. The kidneys were then perfused ex vivo with either a Krebs-bicarbonate solution (Krebs) or a Krebs solution containing 3 mM PCr or an osmotically balanced solution containing 3 mM PCr. Our results indicate that the perfusion of kidneys subjected to 45 min of warm ischemia with solutions containing PCr resulted in significant improvements in GFR, RPF, and V, FRNa and FRH2O compared to KREBS alone. This suggests that the important factor in preservation of kidney function after an initial ischemic insult may be the addition of PCr rather that the electrolyte solution used.

Absorption↗