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Biomedical subjects

R Silva

Publications and source records attributed to R Silva.

At least 91 records · Page 5Linked to original sources
PubMed1994

Effects of glucagon on diuresis, renal plasma flow and glomerular filtration in sheep.

The effects of intravenous infusion of glucagon (100 ng.kg-1.min-1) on diuresis, renal plasma flow and glomerular filtration rate were studied in conscious sheep. Diuresis began to decrease upon initiation of glucagon infusion, down to 50% of its baseline value at the end of glucagon infusion. Glomerular filtration rate was also decreased by 75%. With regard to renal plasma flow, the decrease started at the beginning of glucagon infusion, but remained restricted. It was not possible, from these results, to explain the reduced diuresis by a decrease in renal plasma flow; the observed anti-diuretic effect could be the consequence of a modification of either the filtration coefficient or water tubular reabsorption.

Animals↗
PubMed1993

Cellular mechanisms of estrogen- and dopamine-induced control of glandular kallikrein in the anterior pituitary of the rat.

Glandular kallikrein (GK, a trypsin-like serine protease) exhibits estrogen induction and dopamine repression in rat pituitary lactotrophs. Steroid induction may reflect primary actions to increase selectively the synthesis of specific proteins, or may be part of broad cellular responses secondary to steroid-induced phenotype transitions. This study examined the cellular mechanisms underlying estrogen and dopaminergic control of lactotroph GK using a quantified immunocytochemical approach. Pituitaries from ovariectomized rats exhibited little GK staining. Estradiol treatment for 10 days produced dose-dependent increases in pituitary mass, the percentage of lactotrophs (indicating lactotroph proliferation) and the percentage of GK-positive cells. Also, GK staining intensity was dependent upon estradiol dose, increasing 4-fold between 5 micrograms and 50 micrograms/48 h. Dopamine receptor blockade with haloperidol (2.5 mg/kg/24 h) elicited weak GK immunostaining in 46% of the lactotrophs in the absence of estradiol, and markedly potentiated GK staining intensity elicited with low but not high doses of estradiol. The results suggest that GK induction is a primary estrogen effect, and is not secondary to a phenotype transition: the induction is enhanced by estrogen-induced lactotroph proliferation. Dopaminergic systems strongly inhibit GK induction by low estradiol levels. This dopaminergic modulation may shift the induction of lactotroph GK to physiological events associated with high estradiol levels or low dopaminergic tone.

Animals↗
PubMed1993

Reactivity of cysteinyl, arginyl, and lysyl residues of Escherichia coli phosphoenolpyruvate carboxykinase against group-specific chemical reagents.

Calcium-activated phosphoenolpyruvate carboxykinase from Escherichia coli is not inactivated by a number of sulfhydryl-directed reagents [5,5'-dithiobis(2-nitrobenzoate), iodoacetate, N-ethylmaleimide, N-(1-pyrenyl)maleimide or N-(iodoacetyl)-N'-(5-sulfo-1-naphthylethylenediamine)], unlike phosphoenolpyruvate carboxykinase from other organisms. On the other hand, the enzyme is rapidly inactivated by the arginyl-directed reagents 2,3-butanedione and 1-pyrenylglyoxal. The substrates, ADP plus PEP in the presence of Mn2+, protect the enzyme against inactivation by the diones. Quantitation of pyrenylglyoxal incorporation indicates that complete inactivation correlates with the binding of one inactivator molecule per mole of enzyme. Chemical modification by pyridoxal 5'-phosphate also produces inactivation of the enzyme, and the labeled protein shows a difference spectrum with a peak at 325 nm, characteristic of a pyridoxyl derivative of lysine. The inactivation by this reagent is also prevented by the substrates. Binding stoichiometries of 1.25 and 0.30 mol of reagent incorporated per mole of enzyme were found in the absence and presence of substrates, respectively. The results suggest the presence of functional arginyl and lysyl residues in or near the active site of the enzyme, and indicate lack of reactive functional sulfhydryl groups.

Arginine↗
PubMed1993

Heat shock proteins in Trypanosoma cruzi: identification and localization of HSP70 and HSP60 proteins and structure of HSP60 genes (brief report).

To identify the members of the HSP70 and HSP60 families of Trypanosoma cruzi, we analysed 35S methionine epimastigote cells by two dimensional Western blot. At 29 degrees C, an HSP70 monoclonal antibody (anti-D. melanogaster) recognized eight isotypes. At least five of these were heat-induced. Polyclonal antibody against the 65 KDa antigen (anti-M. tuberculosis) recognized three isotypes with identical molecular weights, but different microliters. Only one isoform was heat induced. The cellular distribution of HSP70 and HSP60 was studied by immunoelectron microscopy. Anti-HSP70 reactive protein was localized in the cytoplasm, mitochondria and nucleus, while anti-HSP60 protein was found in the mitochondrion and in close association with the kinetoplast. To characterize the HSP60 gene and its proteins, we isolated a genomic T. cruzi clone encoding the HSP60 gene. T. cruzi HSP60 genes could be shown to be organized in 2100 nt tandem arrays. RELP in the HSP60 genes revealed that at least three different types of HSP60 genes were encoded in the T cruzi genome. The predicted open reading frame measured exhibits about 50% identity to other HSP60 described. Expression of these HSP60 genes could not be induced by 2 hours heat shock at 37 degrees C. Post-transcriptional mechanisms may be responsible for HSP60 induction in T. cruzi.

Animals↗
PubMed1993

[Postmortem orbital hematomas].

Several cases of post mortem hematoma resulting from harvesting of the eye globes for transplantation, and susceptible of being misinterpreted as representing ante mortem trauma, are presented. Based on these cases the authors make a few considerations about the mechanisms of their production and technical procedures to avoid them.

Adult↗
PubMed1993

[Existence of an antidiuretic reflex in the sheep during food intake].

The effect of eating on glomerular filtration and urine flow was studied in the sheep. Glomerular filtration rate was reduced during eating but the effect disappeared when food was removed. Urine flow showed the same evolution but, after ingestion was stopped, it returned later than glomerular filtration to control values. During the early phases of feed ingestion, an anticipatory anti-diuretic reflex therefore exists. The anti-diuretic response is probably dependent on a simultaneous decrease in glomerular filtration. But the temporary delay between the recovery of glomerular filtration and urine flow after feed is removed suggests the existence of a second factor responsible for the lowered urine flow.

Animals↗
PubMed1991

[Pepsanurin in congestive heart failure].

We have identified a plasmatic substance, "pepsanurin" (PU) obtained by pepsin hydrolysis which inhibits the renal effects of the atrial natriuretic factor (ANF). To investigate whether patients with congestive heart failure (CHF) have increased plasma levels of PU we prepared PU from 10 patients with CHF class IV (NYHA), 9 patients with CHF class II or III and 16 healthy controls. Anesthetized rats were used to test the effects of ANF, 0.5 ug/100 g body weight i.v., before and following the intraperitoneal injection of 0.5 ml of PU. The inhibition of the diuretic and natriuretic effects of ANF was 40.9 +/- 11.9% and 49.8 +/- 12% respectively for control subjects. Corresponding figures for class IV CHF patients were 62.3 +/- 3.1% and 73.8 +/- 3.5% (p less than 0.02) and for class II-III patients 39.2 +/- 7.0% and 53.1 +/- 8.2% (NS). Accordingly, an increased capacity to generate PU may underlie the decreased sensitivity to ANF in patients with advanced CHF.

Adult↗
PubMed1991

[Shortened preoperative preparation in diffuse hyperthyroid goiter: experience in 34 patients].

Conventional preparation of goitrous hyperthyroid patients using lugol and propranolol may take 2 weeks. This period may be shortened using sodium iopodate and dexamethasone. We used 500 mg of sodium iopodate and 1 mg dexamethasone for 4 days in 34 hyperthyroid patients. Surgical indication derived from failure to medical treatment (68%), large goiter (27%) or adverse reaction to PTU (6%). Clinical euthyroidism was achieved after 4 days in all patients. T3 levels decreased from 482 +/- 26.2 to 137.6 +/- 3.7 ng/dl and T4 from 20.6 +/- 1.04 to 15.2 +/- 0.5 micrograms/dl (p < 0.005). Surgery was uneventful in 33 patients, one subject developed supraventricular tachycardia responsive to verapamil. Electron microscopy of the removed thyroid tissue revealed marked decrease of superficial villi and large phagosomes. Thus, sodium iopodate and dexamethasone are effective and safe for preoperative preparation of hyperthyroid patients.

Adolescent↗
PubMed1991

Recovery of myocardial function during coronary artery bypass grafting. Intraoperative assessment by pressure-volume loops.

Radionuclide angiocardiography and left ventricular manometry were performed simultaneously in 12 men undergoing elective coronary artery bypass grafting. Pressure-volume loops constructed from these data allow calculation of stroke work and provide a more complete description of global left ventricular function immediately before cardiopulmonary bypass and at a mean of 18 and 34 minutes after termination of ischemic arrest. Early reperfusion was characterized by significant elevation of end-diastolic pressure (p less than 0.01) without a corresponding increase in end-diastolic volume. With continued reperfusion, end-diastolic volume, calculated stroke work, and cardiac output increased significantly with respect to control (p less than 0.05). Heart rate, ejection fraction, mean arterial pressure, stroke work/end-diastolic volume, and maximal dP/dt remained unchanged during the study period. No new focal abnormalities were detected in regional wall motion. These data indicate that minimal residual impairment of diastolic function exists during the acute recovery from cardioplegic arrest and bypass grafting but improves with further reperfusion. Systolic function appears to normalize more rapidly than diastolic function after ischemic arrest.

Adult↗
PubMed1990

Malignant, non-Hodgkin's lymphomas in Trypanosoma cruzi-infected rabbits treated with nitroarenes.

Use of 2-nitroimidazole, 5-nitrofuran and 5-nitroimidazole compounds in T. cruzi-infected rabbits resulted in a reduction in duration of parasitaemia in comparison with untreated, infected rabbits. The chronic myocarditis associated with Chagas' disease was not, however, prevented in nitroarene-treated rabbits; lymphocytic infiltrates associated with cardiac cell lysis, in the absence of parasites in situ, were present in both treated and untreated rabbits. The carcinogenic effect of each trypanocidal nitroarene used in this study was also assessed. Administration of nitroarenes to rabbits resulted in the appearance of solid tumours in 37.8 per cent of animals that received drug therapy. Untreated, control rabbits in this series did not show tumour growth. Furthermore, malignant, mixed-cell type, non-Hodgkin's lymphomas were seen in 32.4 per cent of the treated rabbits. It seems that a direct relationship could be present between the presence of the nitro group, the trypanocidal cytotoxicity and the prevalence of tumours. Benznidazole cleared up parasitaemias in the shortest time and was associated with 41.6 per cent of lymphoma growths, whereas MK-436 required twice as much time to clear blood parasites, and showed lymphomas in 25 per cent of experimental rabbits. The demonstration of a high prevalence of malignant tumours in addition to the chronic myocarditis of Chagas' disease in nitroarene-treated rabbits is important since indiscriminate use of such compounds currently used to treat T. cruzi infections in man could increase the risk of lymphoma.

Animals↗
PubMed1990

Polarity of kallikrein release and activation in perfused rat kidneys.

The polarity of release and activation of renal kallikrein and its regulation by adrenal hormones was studied in isolated perfused rat kidneys. Bilateral adrenalectomy (AX) produced a decrease in kallikrein and prokallikrein excretion into urine and perfusate of isolated kidneys, as well as in active kallikrein excretion in vivo. One-week treatment with deoxycorticosterone acetate (DOCA 2.5 mg/day) or dexamethasone (DEX 0.25 mg/day) increased the urinary output of active and total kallikrein above AX levels but below control. In contrast, neither corticoid increased enzyme secretion to perfusate. Regardless of AX or corticosteroid treatment, the prokallikrein fraction was 90% of total enzyme in perfusate and only 40% in urine. These results confirm that adrenal steroids are necessary for renal kallikrein synthesis and excretion; however, neither DOCA nor DEX appears to be a unique regulator for release or activation of this enzyme. In addition, whereas the processes of secretion and activation toward the urine are regulated in parallel, kallikrein release to the venous effluent seems to be regulated separately.

Animals↗
PubMed1990

Localization of immunoreactive glandular kallikrein in lactotrophs of the rat anterior pituitary.

Glandular kallikrein (a trypsin-like serine protease) is an estrogen-induced and dopamine-repressed protein in the rat anterior pituitary which predominantly exists as a latent zymogen (prokallikrein). Its regulation, presence in estrogen-induced pituitary tumors in F344 rats, and expression in GH3 cells has suggested a localization in lactotrophs (prolactin-producing cells). This study examined the cellular origin of glandular kallikrein using immunocytochemical techniques. Anterior pituitaries from estrogen-treated rats were fixed and embedded in paraffin (for preparation of semi thick sections; 5 microns) or methacrylate (for preparation of thin sections; 1 micron). Glandular kallikrein immunostaining was readily detected in the perinuclear (Golgi) region of parenchymal cells of the anterior pituitary in both thin and semi thick sections. Two-color double immunoperoxidase staining of thin and semi thick sections indicated that glandular kallikrein was localized in cells containing prolactin (PRL) but not other pituitary hormones. Immunoperoxidase staining of consecutive serial thin sections with alternating antisera confirmed a localization of glandular kallikrein in lactotrophs. The results establish that glandular kallikrein is colocalized with PRL in lactotrophs of the rat anterior pituitary. This is consistent with the hypothesis that the function of anterior pituitary glandular kallikrein is linked to PRL in some fashion--possibly as a PRL-processing protease.

Animals↗