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Biomedical subjects

M E García

Publications and source records attributed to M E García.

At least 37 records · Page 2Linked to original sources
PubMed1997

Inhibitory effect of sulfonylureas on protein phosphatase activity in rat pancreatic islets.

We have measured protein phosphatase (PP) activity in crude homogenates as well as in the total 105.000 x g supernatant and precipitate fractions from normal rat pancreatic islets. On the basis of the inhibition produced by either 1 nM or 1 microM okadaic acid, both PP1 and PP2A activity were present in crude islet homogenates in equivalent proportions (53% and 47%, respectively); PP1 was the main activity present in the precipitate, whereas in the supernatant it was PP2A. Tolbutamide, glybenclamide and glyclazide significantly decreased PP activity in islet homogenates in a dose-dependent manner, with a K10.5 value that in the case of glybenclamide correlated with its Kd for binding site, its EC50 on KATP channel, and its EC50 on insulin release. These data indicate that PPs play a role in the control of insulin secretion and suggest a further possible target for sulfonylureas within their overall action as insulin secretagogues.

Animals↗
PubMed1997

Immunochemical reactivity of Aspergillus fumigatus antigens from different sources.

We have studied the immunochemical and biochemical differences in 12 Aspergillus fumigatus strains isolated from different sources. The enzymatic activity of all these strains were studied by a rapid enzyme detection method (API-ZYM). One of 12 strains studied produced alkaline phosphatase, while two produced chymotrypsin, and three produced trypsin. By SDS-PAGE we studied proteins present in the antigen extracts from all 12 strains. Several of the protein bands were unique and may be used to differentiate the strains. One such protein is the 58 kDa band present in the mycelial extract and the 33 kDa in the culture filtrate. By crossed immunoelectrophoresis, differentiation of the strains isolated from cystic fibrosis patients can be made based on a few specific precipitin arcs developed against anti-Aspergillus rabbit serum.

Journal Article↗
PubMed1997

Immunoreactivity of antigen extracts of Aspergillus fumigatus isolated from different sources.

Allergic bronchopulmonary aspergillosis (ABPA) is the result of hypersensitivity to Aspergillus antigens in patients with long-standing atopic asthma. In the present study mycelial and culture filtrate antigens from Aspergillus fumigatus cultures isolated from diverse sources were tested against sera of 10 ABPA patients and 10 control individuals by an ELISA methodology. The results indicate higher antibody reactivity against both antigens in the sera of ABPA patients, while culture filtrate antigens also gave non-specific reactivity with control sera. Mycelial extracts, in general, were useful in the diagnosis of ABPA.

Journal Article↗
PubMed1995

Clinical expression of rheumatoid arthritis in Chilean patients.

In populations such as Northern Europeans in which the HLA-DR4 subtypes DW14 and Dw4 show strong association with rheumatoid arthritis (RA), these alleles and the double allelic dose of the shared epitope are considered severity markers. The clinical expression of RA varies in different populations, which may be determined by variation in the prevalence of these markers. In the present study we analyzed the expression of RA in 112 consecutive Chilean patients and its relation to the prevalence of genetic factors, prompted by our previous observation that DR4 is weakly associated to RA in this population. Mean age was 50 +/- 14 years; 90% were seropositive and 87% were female, with a disease duration of 10 +/- 8 years. Extra-articular manifestations were found in 38% of patients, rheumatoid nodules in 27%, vasculitis in 8%, and Sjogren's syndrome in 29%. Functional capacity (ACR, 1991) I or II: 82%.15% of patients stopped working. Hand radiographs scored according to Steinbrocker in 89 patients: I, 21%; II, 15%; III, 43%; IV, 21%. In this series, patients with less formal education seemed to have more benign arthritis. In 97 controls and in 65 (56%) RA patients the presence of DRB1 alleles corresponding to DR1 and DR4 serotypes, to DR4-Dw subtypes, and homozygocity, were determined by polymerase chain reaction followed by specific oligonucleotide hybridization. The shared epitope was present in 53% of RA patients and in 30% of controls (P = .0048, odds ratio [OR] = 2.64). A double allelic dose of the epitope was present in 15% of RA patients compared with 4% of controls (P = .026, OR = 4.23). In a subgroup of 31 erosive RA patients we did not find a significant association of disease severity with the shared epitope in a single or double allelic dose. None of the DR4 subtypes that associate with RA in other populations was found significantly more prevalent in our patients. The severity of RA in our study compared with published series was intermediate between British patients with severe RA and Greek patients with milder disease. This may be due to the high prevalence of Dwl3*0403 in our population.

Adult↗
PubMed1994

A red pigment synthesized by an Aspergillus parasiticus mutant as a possible new intermediate in the aflatoxin biosynthetic pathway.

The isolation of a red pigment from an Aspergillus parasiticus mutant obtained by 366 nm u.v. light treatment of A. parasiticus NRRL 2999 is described. Studies of conversion in aflatoxin B1 and G1 suggest that the red pigment could be a possible new intermediate in the aflatoxin biosynthetic pathway not described to date, and this has been verified by studies in gas chromatography/mass spectrometry. The solubility and stability characteristics under refrigeration storage, and the influence of the temperature and the pH on its production by the A. parasiticus mutant were also studied. It grew best at 30 degrees C and pH 6. The red pigment was most soluble in ethyl acetate. The results obtained in water are emphasized where there was high stability.

Aflatoxin B1↗
PubMed1992

Total sialic acid in human and canine platelets does not change with the platelet age.

Total platelet sialic acid (SA) was measured in three experimental conditions: (1) human and canine platelet density subpopulations obtained by centrifugation in arabinogalactan gradients, (2) circulating canine platelets during recovery from experimental immune and mechanical thrombocytopenias, and (3) platelets obtained from a patient with chronic immune thrombocytopenic purpura before and after splenectomy. The density of human and canine platelets is, in part, determined by their age. We found no significant differences in total SA between high-density (HD) and low-density (LD) platelets (9.32 +/- 2.0 vs. 9.55 +/- 1.3 micrograms/mg of platelet protein in dogs and 9.02 +/- 2.3 vs. 9.10 +/- 2.9 micrograms/mg in humans). In the human and canine thrombocytopenic models, the entrance of new platelets from the bone marrow is followed by their aging in the circulation. In these models, no significant changes in total SA content were detected in sequential measurements during the recovery of the thrombocytopenia. Accordingly, we conclude that total SA in human and canine platelets is unrelated to their age in circulation. These results do not support the notion that the loss of SA from membrane glycoproteins determines the recognition and removal of platelets from the circulation.

Animals↗
PubMed1991

Platelet 5-hydroxytryptamine increases with platelet age in dogs.

Thrombocytopenia was induced in mongrel dogs by two mechanisms: immunologically, by intravenous injection of heterologous antiplatelet antibody, and non-immunologically, by circulating the blood through glass beads in anesthetized animals. The platelet content of 5-HT was monitored before and during the recovery of the blood platelet counts. This period is associated with the normalization of the mean platelet survival time and with a progressive increase in the mean age of the circulating platelet population. A continuous increment in platelet 5-HT closely followed the increase in platelet counts in both models of thrombocytopenia, and a strong correlation was found between the platelet age and 5-HT content. These findings support the concept that platelets accumulate 5-HT during their physiological aging process, contradicting the notion that a negative balance in 5-HT content results at the end of their physiological lifespan in circulation. These results are not in conflict with the concept that circulating platelets release and re-uptake 5-HT.

Animals↗
PubMed1990

Changes induced by glucose in the plasma membrane properties of pancreatic islets.

Partially purified membranes obtained from rat pancreatic isolated islets preincubated for 3 min with 3.3 and 16.6 mM glucose were labelled with 1,6-diphenyl-1,3,5-hexatriene to study fluorescence polarization. Other islets, incubated for 5 min with the same glucose concentration, were extracted and phospholipids separated by thin-layer chromatography. The composition of phospholipids of fatty acids was then studied by gas-liquid chromatography. Arrhenius plots of the microviscosity in membranes obtained from islets exhibited two components, a steeper slope below 18 degrees C and a gentler slope above 18 degrees C, indicating greater flow activation energy at temperatures below the transition point. Exposure of islets to 16.6 mM glucose significantly increased the flow activation energy (delta E), below and above the transition point. Islets incubated for 5 min with 16.6 mM glucose showed an increase in the percentage composition of 12:0 and 18:2 together with a decrease in the 20:2 W6 and 22:3 W3 fatty acids esterified to phospholipids. Regardless of these changes, no significant alterations occurred in the proportion of saturated fatty acids or in the double bond index; these measurements therefore did not account for the effects of glucose concentration in flow activation energy. The thermotropic changes reported here might be the consequence of some degree of disorder induced by glucose upon the membrane structure. This order alteration could either favor the membrane fusion which occurs during the emiocytosis or only reflects the consequence of such a process.

Animals↗
PubMed1988

Lipid composition of normal male rat islets.

Lipid composition was studied in fresh isolated islets from normal male rats. Extractable lipids represent 1856 micrograms per mg islet protein. In such extracts, phospholipids and neutral lipids represent 13.5% and 86.5%, respectively. Phosphatidylcholine (45.8%) and phosphatidylethanolamine (20.6%) were the major components of the phospholipid fraction, and phosphatidylinositol (8.9%) was the minor component. Esterified cholesterol (38.5%), cholesterol (25.5%) and free fatty acids (24.4%) were the major components of the neutral lipid fraction. Fatty acids esterified to phospholipids account for 619.7 pmol/islet, and 2710 pmol/islet were esterified to neutral lipids. In the phospholipid fraction, saturated and unsaturated fatty acids were in a similar proportion. Conversely, in the neutral lipids, two-thirds of the fatty acids were unsaturated. The omega 6 family was the main component of the phospholipid unsaturated fatty acids. In the omega 6 and omega 3 families, the long-chain fatty acids represent the main components. In the neutral lipid fraction, a different percentage of each family was found: omega 3 greater than omega 6 greater than omega 9. The long-chain polyunsaturated fatty acids were also predominant species in the omega 6 and omega 3 families. Further studies on the lipid composition of islets, obtained from rats with normal and altered islet functions, could provide new insights into the knowledge of the mechanism of insulin secretion.

Animals↗
PubMed1987

Thyroid hormone binding and deiodination by pancreatic islets: relationship with the in vitro effect upon insulin secretion.

Thyroxine dehalogenation by rat pancreatic islets was studied incubating isolated islets with labelled T4. [125I]T4 added to the incubation medium was deiodinated by the islets with the consequent production of T3, rT3 and iodide. This deiodination process showed a clear glucose-dependence, being significantly increased in the presence of 16.6 mmol/l glucose. The existence of high and low affinity binding sites for T3 was also demonstrated incubating [125I]T3 with islets under different experimental conditions. The properties of these binding sites were greatly influenced by the extracellular concentration of glucose. Addition of T3 to the incubation medium, significantly modified the insulin release, but its effect varied according to the glucose concentration in the medium, i.e. it enhanced the insulin release at a glucose concentration between 2 to 8 mmol/l; it has no effect at 12 mmol/glucose, and significantly inhibited the secretion of insulin in the presence of 16.6 mmol/l glucose. Our results suggest that thyroid hormones might play a direct regulatory effect on insulin secretion, probably mediated by its deiodination and interaction with specific receptors in the islet cell.

Animals↗
PubMed1986

Islet cell population changes induced by short term ovariectomy.

Changes induced in the endocrine pancreas were studied in rats 14 days after ovariectomy. The study was performed in age matched control (C) and ovariectomized (O) rats. The pancreases were stained using the p-aldehyde-fuchsin and the peroxidase (using antiinsulin serum) methods. Morphometric analysis was done using the Weibel technique. The results obtained show a diminution in the total volume of the endocrine pancreas accompanied by an increment in the individual islet volume following the ovariectomy. The last change would be the consequence of an increment in the number of islet cells (mainly the B cell population), without change in cellular volume, i.e., hyperplasia without hypertrophy. These changes might explain the apparent discrepancy regarding the effect of ovariectomy upon insulin secretion when this process is studied using either the total pancreas preparation or the isolated islet model.

Animals↗
PubMed1985

[Hormonal regulation of glucose metabolism in islands of Langerhans].

Insulin secretion and glucose metabolism were simultaneously studied in isolated islets obtained from normal, endocrine-deficient (adrenalectomized, ovariectomized and radiothyroidectomized) rats as well as from this latter group of rats previously submitted to specific substitutive therapy. The islets from all the endocrine-deficient rats showed clear and similar changes in both the insulin secretion and the metabolism of glucose, being the correlation between the degree of these two alterations highly significant. All the above mentioned abnormalities were corrected by the administration of the corresponding substitutive therapy. These results suggest that the hormones involved in this study could modify the B cell insulin secretion by changing their capacity to metabolize glucose.

Adrenal Cortex Hormones↗
PubMed1984

Effect of the removal of different endocrine glands upon insulin secretion and B-cell ultrastructure.

Glucose-induced insulin secretion and B-cell ultrastructure were studied in islets obtained from normal, adrenalectomized, radiothyroidectomized, ovariectomized and orchidectomized rats. Both parameters were also studied in the same experimental groups submitted to specific substitutive therapy. Insulin secretion in response to high glucose was significantly diminished in adrenalectomized, hypothyroid and male castrated rats. Conversely, this secretion was enhanced in ovariectomized rats. These abnormal insulin responses were restored to normal range by specific substitutive therapy. B-cell ultrastructure was markedly altered in hypothyroid and in female and male castrated rats. No significant changes were observed in the adrenalectomized rats. No conspicuous alterations were depicted in the other islet cell populations. The features of the morphological alterations were mainly related to changes in the B-granules and the rough endoplasmic reticulum. Modifications of the other B-cell organelles were less frequent. In the castrated rats, a distinctive feature was the appearance of a finely granulated colloid material. These B-cell alterations, consecutive to changes in the circulating levels of a given hormone, seemed to depend on the chemical structure of the hormone itself rather than on the changes induced in the B-cell secretory function. The ultrastructural changes described were reversed, as in the case of insulin release, by specific substitutive therapy. It is concluded that changes in the circulating levels of the hormones studied are followed by specific alterations in both B-cell secretion and ultrastructure.

Adrenalectomy↗
PubMed1984

Multiple modulators of the glucose-induced net calcium uptake by isolated islets.

Glucose-induced insulin secretion and net calcium uptake were simultaneously studied in isolated islets obtained from normal, adrenalectomized, ovariectomized and radiothyroidectomized rats, as well as from the corresponding hormone deprived rats following the administration of specific substitutive therapy. Both parameters were also studied in islets from normal rats incubated in the presence of Trifluoperazine (TFP). In all these unrelated experimental conditions simultaneous changes were obtained, observed in the release of insulin and the net calcium uptake elicited by glucose. Otherwise, the modifications of these two parameters obtained in the hormone deprived states were brought back to normal when the animals received the specific substitutive hormonal treatment. On the other hand, TFP also induces simultaneous diminution in both glucose-induced insulin release and net calcium uptake by isolated islets. On account of our results, we could suggest that the mechanism involved in the control of the glucose-induced net calcium uptake is actively modulated by adrenal and ovarian steroids and thyroid hormones as well as by calmodulin. Therefore, changes induced either in the level or activity of these modulators will modify the rate of influx and efflux of Ca2+ across the plasma membrane, with the consequent alteration in the mechanism of stimulus: secretion coupling of insulin.

Adrenal Cortex Hormones↗
PubMed1984

[Diarrhea caused by Campylobacter fetus jejuni and other infective agents in children of the rural area of Puriscal, Costa Rica].

Between September 1979 and September 1981 a field study was conducted on the etiology of diarrheal disease in the area of Puriscal, Costa Rica. The presence of enteric pathogens was investigated in the stools of 267 diarrheic children and 190 healthy controls. Both groups belong to yearly cohorts recruited at birth as part of a longitudinal multidisciplinary study of mothers and children. Campylobacter fetus jejuni was identified as the only pathogen in the stools of 24 diarrheic children (9%) and in four healthy controls (2%), a significant difference (p less than 0,05). The clinical features of the episodes were: irritability (77%), blood in stools (35%), anorexia (38,5%), and fever and vomiting (36%). Dehydration was not important among infected children (only one with 5% dehydration). All children received oral salt solutions and only two were treated with antibiotics. Rotaviruses were the main etiologic agents (17%) and Campylobacter ranked second (10,5%). The frequency of enterotoxigenic Enterobacteriaceae was similar in sick children and in controls (10% and 12% respectively).

Anti-Bacterial Agents↗
PubMed1983

Functional and ultrastructural changes induced by short term ovariectomy on pancreatic islets.

The effect of short term ovariectomy and combined estrogen-progesterone treatment on insulin secretion was studied and related to the changes observed in the glucose oxidation, calcium uptake and insulin content, as well as the ultrastructure of pancreatic rat islets. It was found that ovariectomy was followed by an enhanced glucose-induced insulin secretion, glucose oxidation, calcium uptake and insulin content together with striking changes at the ultrastructural level located only in the B cell population. They were represented by the appearance of broad cytoplasmic areas containing an homogeneous fine granular material, enclosing sometimes organelles, B secretory granules with their clear halo significantly enlarged and marked dilation of the rough endoplasmic reticulum. Conversely, in ovariectomized-rats supplemented with estrogen-progesterone, the insulin response as well as the above mentioned metabolic parameters return to normal control values. Although not completely, ultrastructural changes also showed a clear amelioration. On account of our results, we might suggest that insulin secretion is controlled, at least in part, by the circulating levels of estrogen and progesterone throughout their effect on pancreatic islet metabolism. The absence of this control over a short term period produces a reversible increment in B cell function and the appearance of important changes at the ultrastructural level.

Animals↗
PubMed1982

Glucocorticoid-induced changes in insulin secretion related to the metabolism and ultrastructure of pancreatic islets.

The effect of adrenalectomy and dexamethasone-treatment on insulin secretion was studied and related to the changes observed in the glucose oxidation, calcium uptake, cAMP and insulin content, as well as the ultrastructure of pancreatic rat islets. It was found that adrenalectomy was followed by a decreased glucose-induced insulin secretion, glucose oxidation, calcium uptake, cAMP and insulin content without any remarkable change observed at the ultrastructural level. Conversely, adrenalectomized-rats supplemented with dexamethasone showed an increased glucose-induced insulin secretion, glucose oxidation, calcium uptake and cAMP content but a diminished islet insulin content. At the ultrastructural level, a clear picture of increased secretory activity was found, with diminished number of mature B granules and greater number of pale granules, while rough endoplasmic reticulum and Golgi complex frequently appeared hypertrophic. These changes were only observed in the B cells. On account of our results, we might suggest that insulin secretion is partially controlled by glucocorticoid circulating levels throughout their effect on pancreatic islet metabolism.

Animals↗