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Biomedical subjects

M Vargas

Publications and source records attributed to M Vargas.

At least 73 records · Page 4Linked to original sources
PubMed1996

Relationship between parathion and paraoxon toxicokinetics, lung metabolic activity, and cholinesterase inhibition in guinea pig and rabbit lungs.

Kinetic parameters of parathion and paraoxon uptake were determined in isolated and perfused rabbit and guinea pig lungs. They were related to organophosphate-induced lung cholinesterase inhibition. A single pass procedure was used to perfuse the lungs with an artificial medium perfusate containing paraoxon or parathion. The paraoxon and parathion concentrations were determined in the effluents collected at chosen intervals over an 18-min period beginning at the start of perfusion. Three inflowing concentrations (1 nmol/ml, 10 nmol/ml, and 20 nmol/ml) were tested in guinea pig lungs and one (10 nmol/ml) in rabbit lungs. Cholinesterase activity was determined at time 0 and at the end of the experiment. The lungs abundantly extracted paraoxon and parathion over the perfusion period. The extraction ratio was consistently greater in guinea pig than in rabbit lungs. The uptake velocity varied biexponentially in time, suggesting the existence of two compartments. Initial uptake velocities (A, B) and slopes (alpha and beta) were calculated for both compartments. In guinea pigs, A, B and A + B increased proportionally to the supply rate of paraoxon and parathion while a and b remained constant. No significant difference was observed between parathion and paraoxon uptake kinetics. Parameter B was the only one to differ significantly between the two species (rabbits: 8.19 +/- 1.53 for parathion and 6.85 +/- 1.26 for paraoxon; guinea pigs: 12.75 +/- 0.88 for parathion and 15.02 +/- 3.84 for paraoxon). In the lungs of both species, there was a linear relation between y, the percentage of cholinesterase inhibition induced by either organophosphate, and X, the total amount of drug taken up by the lung tissue (in nmol/g/18 min). The following equations were obtained: y = 0.128 x + 0.979 (R2 = 0.89, p < 0.001 for paraoxon); y = 0.120 x - 6.57 (R2 = 0.82, p < 0.005 for parathion). No difference was observed between the two organophosphates. After treatment with the cytochrome P450 inhibitor piperonyl butoxide, the above relations ceased to apply, but this treatment did not influence the kinetics of paraoxon and parathion uptake. The IC50 value calculated for paraoxon, i.e., the paraoxon concentration required to produce 50% inhibition of lung cholinesterase activity, was similar for guinea pigs (2.22 10(-7) +/- 0.22 M) and rabbits (2.36 10(-7) +/- 0.24 M). In conclusion, the biexponential evolution of the velocity of paraoxon and parathion uptake by the lungs thus demonstrates the presence of two pools. The lower extraction ratios calculated for rabbit lungs reflect the lower initial uptake velocity of the second compartment. In the range of concentrations investigated in guinea pigs, no saturable mechanism could be demonstrated for paraoxon and parathion. Cytochrome P450-related lung metabolic activity, through which parathion is converted to paraoxon, appears as a major step in parathion-induced lung cholinesterase inhibition, although it does not appear to affect parathion toxicokinetics.

Animals↗
PubMed1996

Identification and cellular localization of the actin-binding protein ABP-120 from Entamoeba histolytica.

Several actin-binding proteins participate in the morphological changes that occur during amoeboid movement. The gene encoding one of these proteins, the gelation factor ABP-120, was identified and characterized from trophozoites of Entamoeba histolytica. The sequence contains 2574 nucleotides, with an open reading frame of 858 amino acids, giving a protein of 93 kDa belonging to the spectrin family. The N-terminal domain of ABP-120 from E. histolytica revealed a consensus site for actin binding homologous to the actin-binding sites of ABP-120 of Dictyostelium discoideum, alpha-actinin and spectrin. Analysis of the central domain revealed the presence of four repeats of a 73-amino-acid motif constituting 31% of the protein. In addition, a stretch of 105 amino acids was highly divergent when compared with the C-terminal domain of D. discoideum ABP-120. This sequence showed short motifs that are homologous to microtubule-binding domains. We found that ABP-120 from E. histolytica binds to F-actin. In addition, upon motility of the parasite, this protein localized in the pseudopod and the uroid region, implying a role for ABP-120 in movement and capping of surface receptors in E. histolytica.

Actins↗
PubMed1996

Interactions between acetylcholine and substance P effects on lung mechanics in the rabbit.

The pharmacological mechanisms involved in the acetylcholine (ACh)- and substance P (SP)-induced changes in pulmonary mechanics were studied in isolated perfused rabbit lungs. Tracheal pressure (Ptr) and airflow were measured by a Fleisch pneumotachograph and pressure transducers. Air volume, lung resistance (RL) and dynamic compliance (Cdyn) were calculated. ACh induced a dose-dependent increase in Ptr and RL, and a decrease in Cdyn. These effects were strongly prevented by atropine, and partly by SR140333, a neurokinin NK1 receptor antagonist; SR48968, a neurokinin NK2 receptor antagonist; indomethacin and antihistaminics. Ketanserin had no significant protective effect against ACh. SP also induced concentration-dependent increases in RL and decreases in Cdyn. SR140333 and atropine strongly inhibited the effects of SP, while ketanserin, SR48968, antihistaminics and indomethacin did not protect the lungs against this drug. 5-hydroxytryptamine induced no significant change in lung mechanic parameters. Cumulative concentrations of histamine increased RL and decreased Cdyn. We conclude that ACh-induced changes in lung resistance and compliance are in part mediated by a direct effect on airway smooth muscle and in part by the stimulation of C fibers, by the release of histamine from mast cells and by the synthesis of arachidonic acid metabolites. In turn, the effects of SP on lung mechanics are partly due to cholinergic activation.

Acetylcholine↗
PubMed1996

Alveolar Pco2 and Po2 of high-altitude natives living at sea level.

This study was designed to determine whether subjects born at high altitude (HA; 2,000 m or above) who subsequently move to near sea level (SL) develop end-tidal PCO2 (PETCO2) and PO2 (PETO2) values that equal those of SL natives living near SL. A total of 108 male HA natives living near SL were identified by survey of a district in Lima, Peru, and a further 108 male SL natives from the same district were identified as control subjects. Of these subjects, satisfactory data for inclusion in the study were obtained from 93 HA and 82 SL subjects. Mean PETCO2 and PETO2 values were 37.7 +/- 2.5 (SD) and 104.7 +/- 3.2 Torr, respectively, in HA subjects and 37.7 +/- 2.2 and 104.8 +/- 3.0 Torr, respectively, in SL subjects. The average difference between SL natives and HA natives for PETCO2 was 0.07 Torr (-0.64 to 0.78; 95% confidence interval) and for PETO2 was 0.05 Torr (-0.89 to 0.99, 95% confidence interval). The average age and weight of the SL and HA subjects did not differ, but the HA subjects were shorter and tended to have larger vital capacities, consistent with their origin at HA. We conclude that the PETCO2 and PETO2 near SL of SL natives and HA natives do not differ.

Acclimatization↗
PubMed1996

Class V restorations utilizing a new compomer material: a case presentation.

Restorative materials used in the anterior cervical region should be able to restore the affected area in an aesthetic manner, require only a minimal amount of tooth structure removal, and provide protection from further cervical decalcification. The latest generation of restorative materials have combined the qualities of composite resins and glass-ionomers. Some of these materials incorporate resin components into glass-ionomer systems and are termed resin-modified glass-ionomers; others add glass-ionomer particles to acidic polymerizable monomers in a resin matrix and are commonly called "compomers." The learning objective of this case report is to present a step-by-step clinical procedure for restoration of a Class V defect in the maxillary anterior region, using a recently introduced "compomer."

Adult↗
PubMed1995

Protective effect of various antagonists of inflammatory mediators against paraoxon-induced pulmonary edema in the rabbit.

The protective effect of some antagonists of various inflammatory mediators against paraoxon-induced increases in endothelial permeability has been investigated in isolated perfused rabbit lungs. The edema induced by paraoxon has been previously related to a chain reaction mediated by acetylcholine. Lungs were ventilated and blood-free perfused with a constant flow. Arterial and venous pressures and lung weight were continuously recorded. Endothelial permeability was evaluated by measuring the capillary filtration coefficient (Kf,c). Paraoxon (4 x 10(-4) M) was injected in the perfusion circuit, in lungs with or without pretreatment with atropine, ketanserin, clonidine, morphine, indomethacin, and terfenadine plus cimetidine. Paraoxon induced a time-dependent increase in the Kf,c, a maximal effect being recorded 60 min after the injection. All the antagonists used as pretreatment significantly reduced the maximal effect recorded after paraoxon. These results show that muscarinic receptor antagonists, inhibitors of neuropeptides release, cyclooxygenase inhibitors, and 5-hydroxytryptamine and histamine receptor antagonists can protect the lung against the edema induced by paraoxon. This protective effect is due to inhibition of the chain reaction triggered by acetylcholine.

Animals↗
PubMed1995

Publications from the Caribbean in the health sciences.

The investigation reported here examined scientific publications from Barbados, Jamaica, and Trinidad and Tobago over the period 1976-1990. Its purpose was to provide new information about Caribbean research in the health field through assessment of published works. To this end a broad array of journal subject categories was examined using SCISEARCH, an international index of medical and scientific literature. In all, 1,712 titles (articles, editorials, reviews, letters, meeting abstracts, and notes) were selected for analysis. This analysis indicated that Jamaica accounted for about three-quarters of the titles and that there had been a steady increase in the number of titles published over the study period that was most marked in Barbados. Most of the principal authors were affiliated with the University of the West Indies, and nearly one-third of the titles were published in the West Indian Medical Journal, the sole publication from the three study countries that SCISEARCH listed. Most of the subjects covered fell within the area of "general medicine" rather than experimental medicine or public health. However, of the 383 titles dealing with experimental medicine, nearly all (331) originated in Jamaica. In contrast, less than half of the 262 titles in the public health field came from Jamaica, a relatively large number (106) originating in Trinidad and Tobago. Most of the 1,712 titles (63.8%) dealt with topics outside the priority areas identified by the Caribbean Ministers of Health as part of the Caribbean Cooperation in Health (CCH) Initiative.

Authorship↗
PubMed1995

[Hereditary spherocytosis: clinical characteristics and treatment with splenectomy].

PURPOSE: To analyse the clinico-biological characteristics at diagnosis, the clinical course, and the response to splenectomy of a series of patients with hereditary spherocytosis (HS). PATIENTS AND METHODS: The clinical records of 61 patients diagnosed of HS along 30 years were reviewed. The diagnosis was based upon the existence of family history, physical findings, blood cell examination, reticulocyte count, peripheral blood spherocytes, red-cell osmotic fragility, auto-haemolysis, serum haptoglobin, LDH, non-conjugated bilirubin and direct anti-human globulin test. Data regarding the time of diagnosis and clinical course were taken into account in every case. Within the sub-group of 29 patients undergoing splenectomy, the changes in haemoglobin rates and reticulocyte and platelet counts after surgery were evaluated. RESULTS: Of the 61 patients, 35 were men and 26 women; the median age at diagnosis was 13 years (range: 0-64 years). Family history was positive in only 40% of the cases. The mean haemoglobin rate was 112 g/L (range: 46-151 g/L), over 60% of the patients having anaemia. The mean reticulocyte count was 282 x 10(9)/L (range: 31-583 x 10(9)/L), this being above 100 x 10(9)/L in 91% of the cases. Red-cell osmotic fragility with fresh blood was increased in 86% of the cases, and in 97% after blood incubation. Serum haptoglobins were decreased, whereas LDH was increased in 58% of the patients and non-conjugated bilirubin in 72%. Splenomegaly appeared in the clinical course in 87% of the patients; cholelithiasis was present in 31.5% of them. Haemoiytic crises were seen in 45% of patients, aplastic phases in 7%, and transfusion was needed by 16% of the patients to variable extents. Splenectomy was performed in 50% of the instances before 14 years of age (range: 4-64 years), and it increased haemoglobin rates in 40 g/L, anaemia being corrected in all cases; the mean reticulocyte count returned to normal, but thrombocytosis developed after surgery, it being present in 82% of the cases 2-3 months later. CONCLUSIONS: (1) Wide clinical variability is seen in HS, from severe forms requiring frequent transfusion to asymptomatic cases. (2) Highly frequent findings in HS are reticulocytosis and splenomegaly; relatively frequent were anaemia, haemolytic crisis and cholelithiasis, in this order. (3) Anaemia was always corrected after splenectomy, which also rose the haemoglobin rate even in the cases without anaemia, and returned the reticulocyte count to normal values.

Adolescent↗
PubMed1995

Body weight loss during acute hypoxia: effects of increased convective oxygen transport or previous acclimation.

Body weight loss and growth retardation occur in rats exposed to simulated high altitude, which may be related to the hypoxemia-induced reduction in the convective oxygen transport (COT). The present study was thus performed to determine whether transfusion polycythemia, increased affinity of hemoglobin for oxygen, or previous acclimation to hypobaria (factors that increase COT) are able to counteract its effect on body weight during the early period of exposure, which appears to be a suitable parameter to test the effectiveness of acclimatization. Polycythemia was induced in weanling rats by two ip injections of 2.5 ml/100 g b.wt of packed homologous red cells. The rise in hemoglobin O2 affinity was brought about in adult rats by giving them 0.5 g/dl sodium cyanate in the drinking water for 3 weeks. A lower body weight loss during the early period of exposure to hypobaria was seen in treated rats than in controls. However, body weight loss was still important, which would indicate that compensation was probably not complete. When growing rats were acclimated to simulated altitude, a sudden increase in body weight was observed when they were brought back to ground levels. When animals were taken to altitude again, they lost weight at a rate not significantly different to that found in non-acclimated ones. The results obtained indicate that treatments do not prevent the studied effect of hypoxia and suggest that hypophagia and the resultant initial body weight loss and secondary depression of body growth could be considered as protective mechanisms against the environmental challenge, although further investigation will be necessary to confirm the hypothesis.

Acclimatization↗
PubMed1995

[Patients with chronic airflow limitation: effects of the inspiratory muscle training with threshold load valve, built with appropriate technology, associated to nutritional support].

AIM: To assess prospectively the effects of a controlled program of inspiratory muscle training program and nutritional support in patients with chronic obstructive lung disease (COPD). PATIENTS AND METHODS: Twenty-three patients with COPD were randomly assigned into four groups. Group I received a 1000 kcal/day nutritional supplement, given as a casein based enteral nutritional formula; group III was subjected to inspiratory muscle training, using an inexpensive pressure threshold load valve constructed according to the Appropriate Technology principles of the WHO, adjusted at 30% of Maximal Inspiratory Mouth Pressure and received also the nutritional supplement; group IV was trained but did not receive the nutritional supplement and group II was not trained nor supplemented. Patients were studied during three months and monthly, inspiratory muscle function, exercise capacity and anthropometry were measured. RESULTS: A significant improvement in exercise capacity, maximal inspiratory pressure and inspiratory muscle endurance was observed in the four groups throughout the study. Trained subjects had greater improvement in their inspiratory muscle endurance, compared to untrained subjects. Nutritional support had no effect in inspiratory muscle function or exercise capacity. No changes in anthropometric measures were observed. CONCLUSIONS: The pressure threshold load valve used in this study, improved inspiratory muscle endurance and nutritional support had no effect in patients with COPD.

Aged↗
PubMed1994

SEM comparison of acid-etched, CO2 laser-irradiated, and combined treatment on dentin surfaces.

Research into polymer systems capable of bonding to dentin and enamel have resulted in improved bond strengths that allow more conservative restoration and strengthening of teeth. However, pretreatment of the dentin and enamel of various sorts, including exposure to laser energy, have been espoused to enhance this bonding. This study investigated the effects of two pretreatments, acid and CO2 laser exposure, both alone and in combination, on the surface topography of prepared dentin specimens as observed by scanning electron microscopy. Eighteen dentin specimens were flat-sanded with 600 grit sandpaper and exposed to 10% maleic acid and CO2 laser both alone and in combination. SEM observation suggested that laser treatment prior to acid etching could increase the resistance of the smear layer to acid removal, that laser exposure after acid treatment could expose a porous topography suggestive of the underlying dentin inorganic structure by way of vaporization of the collagen surface left after acid demineralization, and that these effects varied in degree with the laser exposure energy.

Acid Etching, Dental↗
PubMed1994

Early diagnosis of CMV infection by detection of pp65 antigen in 91 renal transplant recipients.

We evaluated how accurately a CMU antigenemia test correlated with classical CMU infection markers. We studied 91 kidney transplant recipients from February 1991 to June 1992. Antigenemia (pp65 antigen) was positive in 100% of cases of primary infection and in 70% of cases of reactivation and/or reinfection. Furthermore, antigenemia detected more infections (71%) than viremia (16%). The antigenemia test proved to be highly specific: it remained consistently negative in 22 seronegative patients, as well as in 19 of 20 seropositive recipients without recurrent infection. pp65 Antigen in the polymorphonuclear leukocytes was detected earlier than, or simultaneously with, virus culture in 78% of cases and became positive before serologic tests of primary and secondary infection in nearly 90% of cases. Most importantly, the antigenemia test detected all of the symptomatic cases.

Adolescent↗
PubMed1994

Inhibitory effect of an alpha 1-adrenergic antagonist on erythropoiesis in normoxic or hypoxic mice.

The present study was undertaken to assess the effect of prazosin, a selective postsynaptic alpha 1-adrenergic receptor blocking agent, on normoxic and hypoxic mice, in order to evaluate experimentally its use in the treatment of the excessive erythrocytosis that characterizes chronic mountain sickness. The drug, injected intraperitoneally to adult mice at a dose of 400 micrograms/kg per day, induced a significant depression of the rate or erythropoiesis, as measured by red blood cell 59iron uptake, with a decrease in the hematocrit from the 3rd day. The drug also inhibited the oxygen-dependent secretion of erythropoietin (estimated by the plasma immunoreactive hormone concentration) in hypoxemic mice when injected between 0 and 2 h after initiation of the hypoxic stimulation. When injected daily into mice exposed to intermittent hypobaric hypoxia, prazosin limited the degree of polycythemia or induced a sustained decrease in the hematocrit when polycythemia was already present due to previous exposure. It is postulated that the drug, by reducing the peripheral vascular resistance seen during hypoxia, could increase renal blood flow, thus improving the renal oxygen supply and partially restoring the imbalance between gas supply and demand, which drives erythropoietin formation.

Adrenergic alpha-1 Receptor Antagonists↗