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Biomedical subjects

A Garcia

Publications and source records attributed to A Garcia.

At least 271 records · Page 15Linked to original sources
PubMed1990

Conformation in solution of yeast tRNA(Asp) transcripts deprived of modified nucleotides.

A synthetic gene of yeast aspartic acid tRNA with a promoter for phage T7 RNA polymerase was cloned in Escherichia coli. The in vitro transcribed tRNA(Asp) molecules are deprived of modified nucleotides and retain their aspartylation capacity. The solution conformation of these molecules was mapped with chemical structural probes and compared to that of fully modified molecules. Significant differences in reactivities were observed in Pb2+ cleavage of the RNAs and in modification of the bases with dimethyl sulphate. The most striking result concerns C56, which becomes reactive in unmodified tRNA(Asp), indicating the disruption of the C56-G19 base pair involved in the D- and T-loop interaction. The chemical data indicate that unmodified tRNA(Asp) transcripts possess a relaxed conformation compared to that of the native tRNA. This conclusion is confirmed by thermal melting experiments. Thus it can be proposed that post-transcriptional modifications of nucleotides in tRNA stabilize the biologically active conformations in these molecules.

Base Sequence↗
PubMed1990

Bone reactions around transplanted roots. A 5-month quantitative study in dogs.

The aim of this experiment was to study endosteal bone reactions around roots transplanted into an edentulous crest, and the role, if any, of periodontal ligament (PDL) remnants preservation. After extraction of premolars and healing of the crests, 20 roots in 5 dogs were transplanted into bone cavities prepared in the edentulous areas. Roots implanted in the lower and upper right cavities had their PDL remnants preserved while those grafted in the left cavities had their surface planed and dried. After 5 months, the roots with surrounding bone were removed. 2 bone areas were delineated at the mesial aspect of each root, one immediately adjacent to the alveolar wall and the other distal to it. Results demonstrated that bone volume was higher in the proximal versus distal area in the maxilla and mandible preserved groups. The adipocyte content of the marrow spaces, an index of bone maturation, was less pronounced in the proximal versus distal areas in the preserved groups. The number of osteoclasts was higher in the proximal zone in the preserved groups as were the extents of the different bone remodeling activities. The results indicate that the organization of PDL around transplanted roots is associated with rearrangement of the bone tissue surrounding the grafts. This process of long duration might be an adaptation to the likely low mechanical strains applied on bone through the root. Transplantation of PDL-damaged roots did not induce such events in the surrounding bone which had acquired the structure of an edentulous crest.

Adipose Tissue↗
PubMed1990

Transformation by v-myb correlates with trans-activation of gene expression.

The v-myb oncogene of avian myeloblastosis virus causes acute myelomonocytic leukemia in chickens and transforms avian myeloid cells in vitro. Its protein product p48v-myb is a nuclear, sequence-specific, DNA-binding protein which activates gene expression in transient DNA transfection studies. To investigate the relationship between transformation and trans-activation by v-myb, we constructed 15 in-frame linker insertion mutants. The 12 mutants which transformed myeloid cells also trans-activated gene expression, whereas the 3 mutants which did not transform also did not trans-activate. This implies that trans-activation is required for transformation by v-myb. One of the transformation-defective mutants localized to the cell nucleus but failed to bind DNA. The other two transformation-defective mutants localized to the cell nucleus and bound DNA but nevertheless failed to trans-activate. These latter mutants define two distinct domains of p48v-myb which control trans-activation by DNA-bound protein, one within the amino-terminal DNA-binding domain itself and one in a carboxyl-terminal domain which is not required for DNA binding.

Amino Acid Sequence↗
PubMed1990

Bronchodilators in patients with chronic obstructive pulmonary disease on mechanical ventilation. Utilization of metered-dose inhalers.

Bronchodilators are used widely in the acute exacerbations of chronic obstructive pulmonary disease (COPD), although their effectiveness is not clearly established. We used three bronchodilators in 20 patients with COPD who were being mechanically ventilated. Two of the bronchodilators, ipratropium bromide and salbutamol, were administered from metered-dose inhalers (MDI) through an adapter to the endotracheal tube, and the third, aminophylline, was administered in the form of intravenous infusion. Before administering each drug, peak airway pressure, end-inspiratory pressure, resistive pressure, and auto positive end-expiratory pressure (auto-PEEP) were measured, and inspiratory resistance (Rins) and compliance were calculated. Heart rate (HR) and blood pressure were also recorded, and arterial pH and blood gas determinations were made. These measurements were repeated 60 min after the administration of aminophylline, 15 and 60 min after administering salbutamol, and 30 and 60 min after administering ipratropium bromide. With these three drugs, airway pressures were reduced, as well as auto-PEEP and Rins, with respect to basal values (p less than 0.05). The changes in compliance were only significant with salbutamol (p less than 0.05). HR was only significantly modified with aminophylline (p less than 0.05). No blood gas change was observed with any of the three drugs. It can be concluded that: (1) the three drugs used in this study were equally effective in producing significant bronchodilation in patients on mechanical ventilation for severe acute exacerbation of COPD; (2) the administration of bronchodilators by MDI in intubated patients through a special adapter was as effective as the intravenous administration of aminophylline.

Aged↗
PubMed1990

Human chorionic gonadotropin and relaxin concentrations in early ectopic and normal pregnancies.

The present study was performed to investigate whether determination of serum relaxin concentrations would allow assessment of the gestation further than that provided by determination of hCG. Serum relaxin concentrations were quantified in women with resorbing ectopic gestations (as documented by declining titers of beta-hCG). The control group consisted of individuals with intrauterine pregnancies. As an additional control, we studied pregnancies conceived through ovulation induction, which usually have an increased volume of relaxin-secreting luteal tissue. On days 39-70 of gestation, the mean serum relaxin concentrations were significantly lower in ten resorbing ectopic gestations (P less than .001, permutation test) than in the normal control group of 13 intrauterine pregnancies. The median serum relaxin concentrations in patients who had ovulation induction with Pergonal were substantially higher than the median for all normal controls; values in clomiphene citrate-treated patients were within the normal range. These data suggest that relaxin secretion correlates with luteal function in both normal and abnormal gestations and reflects the status of the pregnancy. Thus, relaxin may serve as a useful clinical marker.

Adolescent↗
PubMed1990

Evaluation of determination of lactate dehydrogenase isoenzyme 1 by chemical inhibition with perchlorate or with 1,6-hexanediol.

We have evaluated the determination of lactate dehydrogenase (EC 1.1.1.27) isoenzyme 1 activity by chemical inhibition of the other isoenzymes with perchlorate and with 1,6-hexanediol. In the hexanediol method, we studied the effect of the duration of incubation with the inhibitor; a 5-min incubation yielded results closest to those of an immunochemical technique (Isomune-LD). The perchlorate method was the most precise, and the hexanediol method the least, although for none of the techniques did the coefficient of variation exceed the medically acceptable limit prescribed by the College of American Pathologists. Pairwise correlation among the immunoprecipitation, electrophoretic, and chemical inhibition methods was good (r greater than 0.991), although the differences between means were statistically significant (except for the comparison of the two chemical inhibition methods). Because of its ease, low cost, and precision, we recommend the perchlorate method for routine use.

Adult↗
PubMed1990

[Autografts and tooth transplants. Operative indications].

In order to evaluate the prognosis in tooth transplant procedure the literature on this subject was reviewed. The survival of the periodontal ligament is necessary to prevent ankylosis and root resorption. In order to obtain optimal clinical results, the following guidelines are proposed: preparation of the recipient site 2 weeks prior to graft placement, preservation of intact Pdl at time of extraction, rapid reimplantation of tooth in new socket, short term contention (2-3 weeks); endodontic therapy 8-10 weeks after tooth transplantation.

Adolescent↗
PubMed1990

Dietary patterns and nutrient intakes of toddlers from low-income families in Denver, Colorado.

Over a 2-year period, dietary and socioeconomic data were collected from 793 food records of 90 toddlers, aged 1 to 2 years, who were predominantly U.S. Hispanics living in low-income households in Denver, CO. This study was part of a larger investigation designed to assess the efficacy of vitamin and mineral supplements in young children. The toddlers were randomly assigned to one of five treatment groups: multivitamin; multivitamin and iron; multivitamin, iron, and zinc; multivitamin and zinc; or placebo. Three-day food records that were collected from the toddlers at the beginning of the study, at 3 months, and at 6 months were used to assess the dietary and nutrient intakes. Meal patterns were devised on the basis of the frequency of food consumption and common food combinations. Nutrient values were calculated using a diet analyzer program. Nutrient analysis of the toddlers' diets indicated that iron and magnesium were consumed least frequently, whereas more than adequate amounts of protein (193% of the Recommended Dietary Allowance) and sodium (207% of minimum requirements for healthy persons) were consumed. No significant differences in nutrient intakes were observed among the treatment groups, suggesting that the vitamin and mineral supplements had no effect. A difference in energy intake was observed over time with the 6-month and 3-month intakes significantly higher than the initial intakes. There was also a high consumption of carbonated beverages. Despite the low income levels of the families, these toddlers were consuming adequate amounts of food; however, an educational component aimed at reducing the toddlers' high intakes of protein, sodium, and carbonated drinks may help improve the present feeding practices of the mothers.

Analysis of Variance↗
PubMed1989

Carbachol and histamine stimulation of guanine-nucleotide-dependent phosphoinositide hydrolysis in rat brain cortical membranes.

Guanine nucleotides have been shown to stimulate phosphoinositide breakdown in brain membranes, but no potentiation of such an effect by agonist was demonstrated. We have studied the effect of carbachol and histamine on guanosine 5'-[gamma-thio]triphosphate (GTP[S]) stimulation of inositol phosphates formation in [3H]inositol-labelled rat brain cortical membranes. In this preparation, GTP[S] enhancement of phosphoinositide hydrolysis required the presence of MgATP and low Ca2+ concentration (100 nM). Carbachol potentiation of the GTP[S] effect was only observed when 1 mM-deoxycholate was also added. Under these conditions, stimulated production of [3H]inositol phosphates was linear for at least 15 min, and [3H]inositol bisphosphate [( 3H]IP2) accounted for approx. 80%, whereas the amount of [3H]inositol trisphosphate [( 3H]IP3) was very low. Stimulation by GTP[S] was concentration-dependent (half-maximal effect at 0.86 microM), and its maximal effect (815% over basal) was increased by 1 mM-carbachol (1.9-fold) and -histamine (1.7-fold). Both agonists decreased the slope index of the GTP[S] concentration/effect curve to values lower than unity, suggesting the appearance of some heterogeneity in the population of guanine-nucleotide-binding proteins (G-proteins) involved. The carbachol and histamine effects were also concentration-dependent, and were inhibited by atropine and mepyramine respectively. Fluoroaluminate stimulated phosphoinositide hydrolysis to a higher extent than GTP[S] plus carbachol, and these stimulations were not additive, indicating that the same polyphosphoinositide phospholipase C-coupled G-protein mediates both effects.

Aluminum↗
PubMed1989

Free and conjugated plasma homovanillic acid in schizophrenic patients.

It has recently been suggested that the plasma level of homovanillic acid (HVA) may provide an index of central dopaminergic activity in humans. Clinical studies have shown that in schizophrenic patients, plasma HVA levels increase with the severity of psychopathology. However, these studies only considered the plasma free HVA fraction whereas investigations on conjugated HVA in humans are sparse and results remain controversial. The aim of this study was to measure both plasma free and conjugated HVA in healthy volunteers and drug-free schizophrenic patients. The mean values and the ranges of plasma free HVA in volunteers and patients were similar to those described in the literature. A substantial and significant increase in plasma free HVA was observed in schizophrenic patients compared with normal subjects. In contrast, plasma conjugated HVA was significatively decreased in schizophrenics. The plasma total HVA was nevertheless higher in schizophrenics compared with controls. No significant correlations were observed between plasma HVA levels and the clinical features of schizophrenic patients rated by various psychiatric scales. These findings suggest that there is an imbalance between plasma free and conjugated HVA in schizophrenic patients, who present an increase in total HVA when compared with controls. Paranoid schizophrenic patients, who present mainly positive symptoms, show the most marked plasma free/conjugated HVA imbalance.

Adolescent↗
PubMed1989

Age-related changes in the motor response to environmental novelty in the rat.

To examine age-related changes in responsiveness to environmental novelty, 3-, 12-, and 24-month-old male Fischer 344 rats were maintained on a restricted diet and exposed to a modified open field for 10 min on each of 10 consecutive days. On the first day of testing, animals of all groups showed equal amounts of rearing. While the 3-month animals continued to show approximately the same levels of rearing until the 8th day, by day 5, the older groups (12- and 24-month) had significantly reduced their rearing. Conversely, grooming was initially highest among the 24-month-old animals. While 3- and 12-month rats showed habituation of grooming, the oldest animals failed to habituate their grooming response by day 5. By day 10, there were no significant differences among the groups in either rearing or grooming. Although food was available in the center of the modified open field, there was little eating and there were no differences among groups. However, all animals did eat quickly when food was made available in their home cages. Thus, all animals displayed a profile of stress-related responses to open field exposure. Plasma corticosterone levels likewise were elevated in the modified open field. Some, but not all, components of this response profile habituated over the 10 days of exposure. Three-month-old animals responded to the novelty predominantly by rearing and 24-month animals predominantly by grooming. This suggests that with aging, locomotor responses to stress are replaced by a more self-directed form of displacement activity.

Aging↗
PubMed1989

[Retinitis photoelectrica caused by electro-welding].

The authors report on a student who developed bilateral photoretinitis as a result of failing to use a welding shield properly while arc-welding. The case is unusual in that no symptoms of photophthalmia occurred at any time. The course of the accident is described and the special features of the case are discussed.

Accidents, Occupational↗