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Biomedical subjects

M A Silva

Publications and source records attributed to M A Silva.

At least 55 records · Page 3Linked to original sources
PubMed1992

Effects of tityustoxin and ouabain on release of acetylcholine from slices of cortex from the rat brain and on the acetylcholine content of cytoplasmic and crude vesicular fractions.

In this paper, the effects of tityustoxin and ouabain on the release and mobilization of ACh from cytoplasmic and vesicular stores of slices of cortex from the brain of the rat are described. Tityustoxin induced an increase of release of ACh which was time-dependent and this effect was accompanied by a concomitant decrease of the ACh, measured in cytoplasmic and crude vesicular fractions. Unlike tityustoxin, ouabain did not increase the release and synthesis of ACh during a 2 min period of stimulation but later, at 5, 10 and 15 min, ouabain increased the release and synthesis of ACh from incubated slices of cortex. After 10 min, ouabain caused a reduction of the content of ACh from cytoplasmic and crude vesicular fractions.

Acetylcholine↗
PubMed1992

Calcium transport by corn mitochondria : evaluation of the role of phosphate.

Mitochondria from some plant tissues possess the ability to take up Ca(2+) by a phosphate-dependent mechanism associated with a decrease in membrane potential, H(+) extrusion, and increase in the rate of respiration (AE Vercesi, L Pereira da Silva, IS Martins, CF Bernardes, EGS Carnieri, MM Fagian [1989] In G Fiskum, ed, Cell Calcium Metabolism. Plenum Press, New York, pp 103-111). The present study reexamined the nature of the phosphate requirement in this process. The main observations are: (a) Respiration-coupled Ca(2+) uptake by isolated corn (Zea mays var Maya Normal) mitochondria or carbonyl cyanide p-trifluoromethoxyphenylhydrazone-induced efflux of the cation from such mitochondria are sensitive to mersalyl and cannot be dissociated from the silmultaneous movement of phosphate in the same direction. (b) Ruthenium red-induced efflux is not affected by mersalyl and can occur in the absence of phosphate movement. (c) In Ca(2+)-loaded corn mitochondria, mersalyl causes net Ca(2+) release unrelated to a decrease in membrane potential, probably due to an inhibition of Ca(2+) cycling at the level of the influx pathway. It is concluded that corn mitochondria (and probably other plant mitochondria) do possess an electrophoretic influx pathway that appears to be a mersalyl-sensitive Ca(2+)/inorganic phosphate-symporter and a phosphate-independent efflux pathway possibly similar to the Na(2+)-independent Ca(2+) efflux mechanism of vertebrate mitochondria, because it is not stimulated by Na(+).

Journal Article↗
PubMed1991

Kainate and quisqualate effects on rat presynaptic cortical receptors are metabotropic and non-additive.

The effects of quisqualate and kainate on synaptosomal inositol phosphate (InsP) labelling, 45Ca influx and intrasynaptosomal free calcium ([Ca2+]i) were investigated. Each agonist caused a concentration-dependent increase in both [Ca2+]i and InsP labelling: quisqualate, however, produced significantly larger responses in both parameters and at lower EC50 values. Neither quisqualate or kainate significantly affected 45Ca influx into synaptosomes, indicating that the observed increases in [Ca2+]i were due to mobilisation from intracellular stores. The concentration-dependent increases in [Ca2+]i promoted by quisqualate and kainate were monophasic, whereas the increases in InsP formation fitted well to a biphasic curve. The EC50 values suggest that both kainate and quisqualate initially mobilise calcium from inositol 1,4,5-trisphosphate (Ins 1,4,5-P3)-sensitive stores and that the resultant increases in [Ca2+]i will, above a certain threshold, promote further increases in InsP production by stimulation of Ca(2+)-dependent phospholipase C. When saturating concentrations of kainate and quisqualate were used in combination, the effects on both InsP labelling and [Ca2+]i were not additive but were slightly higher than those produced by kainate alone: combined administration of the two agonists had no effect on 45Ca influx. These results suggest that kainate acts as a partial agonist at the presynaptic quisqualate metabotropic glutamatergic receptor.

Animals↗
PubMed1991

Functional and ultrastructural evaluation of myocardial protection provided by intermittent coronary sinus perfusion in the isolated dog heart.

1. The protection offered by intermittent perfusion of cardioplegic solution through the coronary sinus was investigated in isovolumic blood-perfused dog heart preparations submitted to 60 min of ischemia and 45 min of reperfusion. 2. The preparations were divided into three treatment groups: a) coronary sinus, consisting of preparations (N = 10) perfused through the coronary sinus under 40 cm water pressure; b) aortic, consisting of preparations (N = 10) perfused through the aortic stump under 100 mmHg pressure; c) control, consisting of hearts (N = 9) that were not perfused with cardioplegic solution. 3. Properties of contractile capacity and relaxation were markedly impaired in the control group but were preserved to a comparable extent in the groups perfused with cardioplegic solution through the aorta and coronary sinus. Developed pressure decreased in the control group (before ischemia: 70 +/- 5.5 mmHg; after reperfusion: 35 +/- 12 mmHg; P less than 0.05) and didn't vary in the aortic group (from 69 +/- 4 mmHg to 65 +/- 13 mmHg; P greater than 0.05) and coronary sinus group (from 69 +/- 4.6 mmHg to 60 +/- 10 mmHg; P greater than 0.05). Myocardial relaxation was evaluated by the +/- dp/dt ratio. In the control group there was impairment of myocardial relaxation as indicated by an increase of this index after reperfusion (from 1.05 +/- 0.05 to 1.46 +/- 0.23; P less than 0.05), whereas in the aortic (from 1.10 +/- 0.13 to 1.15 +/- 0.20; P greater than 0.05) and the coronary sinus (from 1.03 +/- 0.14 to 1.08 +/- 0.16; P greater than 0.05) groups there was no variation. Ultrastructural changes in the myocardium were negligible in all three groups at the end of reperfusion. 4. We conclude that intermittent perfusion of a hypothermic cardioplegic solution through the coronary sinus is effective for the protection of the myocardium during total ischemia.

Animals↗
PubMed1991

[Acipimox in primary hyperlipidemias: safety and efficacy evaluated in six months].

The efficacy and tolerance of 750 mg of Acipimox was tested in 38 pts with primary dyslipidemias: 20 type IIa, 12 type IIb, and 6 type IV. All pts had been poor responders to a 2 month diet according to the recommendations of the National Cholesterol Education Program. Clinical examination, eye fundus, and the following laboratory tests: total cholesterol (TC), HDL, triglycerides (TG), total bilirubin, alkaline phosphatase, oxalacetic and pyruvic transaminases, uric acid, plasmatic creatinine, albumin, postprandial glucose test, hematocrit, white blood and platelet count were performed 60 days before drug initiation, 60 and 180 days after treatment had been started. No side effects were observed (myositis, visual gastrointestinal). 50% of the pts had slight to moderate flushing which appeared the first 3 days and lasted 14 +/- 7 days after treatment had been started. Plasmatic creatinine increased from 0.89 to 1.86 mg/dl in pt with one kidney, returning to normal levels 30 days after Acipimox interruption. After 180 days of therapy in the IIa group TC was -27% (p < 0.001), HDL + 15% (p < 0.001); in the IIb group: TC-23% (p < 0.001), HDL +9% (NS), TG -48% (p < 0.001); and in the IV group: TC-10% (p < 0.05), HDL +20% (p < 0.001), TG-53% (p < 0.001). Acipimox is well tolerated and is useful as a lipid-lowering drug in type IIa, IIb and IV dyslipidemias. Further studies are necessary to clear effects of the drug on renal metabolism and on long term survival of coronary pts.

Adolescent↗
PubMed1990

Choline oxidase chemiluminescent assay, after removal of eserine from medium, of acetylcholine released in vitro from brain slices.

A chemiluminescent method has been used recently for the determination of acetylcholine with limitations such as the presence of a cholinesterase inhibitor in the incubation medium, which is indispensable for the study of acetylcholine release by various agents. A modified procedure is presented in which the cholinesterase inhibitor eserine (physostigmine) is extracted from the medium. The results showed complete recovery when labelled acetylcholine was used. This modified procedure was used to determine the release of acetylcholine evoked by tityustoxin and ouabain. The results were comparable to those obtained by bioassay using a strip of guinea pig ileum.

Acetylcholine↗
PubMed1989

[Echographic imaging of absence of follicular rupture. Endocrinologic aspects].

Since Jewelewicz in 1975 first described the luteinization of an unruptured follicle (LUF), clinical evidence for the importance of this syndrome has been given by various groups of investigators. Luteal phase of 14 cycles with ultrasound evidence of unruptured follicles were studied with plasmatic determination of levels of FSH, LH, prolactin, 17 B estradiol and progesterone each one day. Two groups were defined. One, with "ovulatory ranges" of progesterone, probably LUF syndrome and another, with "anovulatory levels", probably follicular cysts.

Estradiol↗
PubMed1989

[Syphilitic aneurysm communicating with an aortic sinus of Valsalva. A case report].

The authors present the case of a 27-year old woman with an aneurysm, possibly originating from an ectopic coronary sprout and communicating with the right anterior sinus of Valsalva. Secondary syphilitic lesions were observed. By virtue of its great size and localization, this aneurysm produced obstruction of the outlet of the right ventricle and dislocation of the left coronary artery. The authors conclude that this aneurysm was a congenital anomaly because of its great volume, configuration, the way it opened in the aortic right anterior sinus of Valsalva, the normal aortic wall and valve, and normal sinuses of Valsalva, observed at surgery. The follow-up was uneventful.

Adult↗
PubMed1989

Cytoadherence in human falciparum malaria as a cause of respiratory distress.

The ultrastructure of three cases of fatal human falciparum malaria was studied in order to identify the cytoadherence of the endothelial cells in relation to parasitized red blood cells and septal interstitial changes which could be related to respiratory distress. Two cases showed marked endothelial oedema narrowing the capillary lumen with areas of adherence preferentially related to knobs, accompanied by septal interstitial oedema. One case showed no endothelial cells oedema, no knobs in parasitized red blood cells with no cytoadherence, no septal interstitial oedema and no respiratory distress. Cytoadherence seems to be the mechanism responsible for the septal pulmonary changes in severe falciparum malaria.

Animals↗
PubMed1979

Assay of human interferon in Vero cells by several methods.

Four methods for the assay of human interferon in Vero cells were compared based on the inhibition of viral cytopathic effect (CPE) in tubes, the inhibition of CPE in microplates, the reduction of plaques, and the inhibition of quantitative hemadsorption. For inhibition of CPE, Sindbis virus, vesicular stomatitis virus, poliovirus type 2, and vaccinia virus were used for challenge. In the plaque reduction method, Sindbis virus, vesicular stomatitis virus, and poliovirus were employed, and Newcastle disease virus was used in the quantitative hemadsorption assay. Sindbis virus was most susceptible to interferon in those tests measuring inhibition of CPE, but vesicular stomatitis virus was as sensitive in the plaque reduction method. Highest titers of interferon were recorded in microplates, especially with Sindbis virus as the challenge agent, followed by the quantitative inhibition assay. The CPE inhibition method was the simplest, and the quantitative hemadsorption assay was the most rapid to perform. Reproducibilities, as shown by the coefficient of variation, were 15, 39, and 59% for plaque reduction, CPE inhibition in tubes, and CPE inhibition in microplates, respectively.

Animals↗
PubMed1976

On estimating non-additive genetic parameters in chickens.

Several economically important traits in two Leghorn populations (over 9000 birds) were examined for additive and non-additive components of genetic variance and sex-linked effects. Data were analysed by two different statistical models based on least-squares procedures. 2. Six different covariances were first calculated between relatives; i.e., full-sibs 3/4-sisters, half-sisters, dam-daughters, grandam-granddaughters and aunt-nieces. 3. From the covariances, weighted least-squares equations were used to obtain estimates of variance components for additive genetic, dominance, maternal and sex-linkage effects. 4. The estimates of non-additive components were highly variable but generally small compared with the additive genetic estimates. 5. In general this study suggests that for most traits, with the possible exception of rate of egg production, there is relatively little non-additive genetic variation. 6. The consequences of possible negative correlations between additive effects and maternal effects are considered as they might apply to egg production in poultry.

Animals↗