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Biomedical subjects

V L Silva

Publications and source records attributed to V L Silva.

11 recordsLinked to original sources
PubMed2005

Differential vulnerability of the rat retina, suprachiasmatic nucleus and intergeniculate leaflet to malnutrition induced during brain development.

We investigated in young rats the effects of malnutrition on the main structures of the circadian timing system: retina, hypothalamic suprachiasmatic nuclei (SCN), thalamic intergeniculate leaflet, retinohypothalamic- and geniculohypothalamic tracts. Control rats were born from mothers fed a commercial diet since gestation, and malnourished rats from mothers fed a multideficient diet since gestation (GLA group) or lactation (LA group). After weaning, pups received the same diet as their mothers, and were analysed at postnatal days 27, 30-33 and 60-63. Brain sections were processed to visualise in the SCN neuropeptide Y immunoreactivity and terminal labeling after intraocular tracer injections. Nissl staining was used to assess cytoarchitectonic boundaries of the SCN and cell features in retinal whole mounts. Cell counts, morphometric and densitometric analysis were performed. Compared with controls, the total retinal surface was reduced and the topographical distribution of retinal ganglion cells was altered in malnourished rats, with changes in their density. Alterations were also detected in the SCN dimensions in the GLA and LA groups at one and two postnatal months, as well as in the SCN portion occupied by the retinal input in the GLA group at days 30-33, but not in the NPY-containing geniculohypothalamic tract. The present data point to subtle changes, with a low and differential vulnerability to early malnutrition, of structures involved in circadian timing regulation. Furthermore, the present findings suggest that the altered circadian rhythmicity previously documented in malnourished rats cannot be ascribed to impaired development of the retino- and geniculohypothalamic projections to the SCN.

Age Factors↗
PubMed2003

Circadian rhythms in blood pressure in free-ranging three-toed sloths (Bradypus variegatus).

Blood pressure (BP) profiles were monitored in nine free-ranging sloths (Bradypus variegatus) by coupling one common carotid artery to a BP telemetry transmitter. Animals moved freely in an isolated and temperature-controlled room (24 degrees C) with 12/12-h artificial light-dark cycles and behaviors were observed during resting, eating and moving. Systolic (SBP) and diastolic (DBP) blood pressures were sampled for 1 min every 15 min for 24 h. BP rhythm over 24 h was analyzed by the cosinor method and the mesor, amplitude, acrophase and percent rhythm were calculated. A total of 764 measurements were made in the light cycle and 721 in the dark cycle. Twenty-four-hour values (mean +/- SD) were obtained for SBP (121 +/- 22 mmHg), DBP (86 +/- 17 mmHg), mean BP (MBP, 98 +/- 18 mmHg) and heart rate (73 +/- 16 bpm). The SBP, DBP and MBP were significantly higher (unpaired Student t-test) during the light period (125 +/- 21, 88 +/- 15 and 100 +/- 17 mmHg, respectively) than during the dark period (120 +/- 21, 85 +/- 17 and 97 +/- 17 mmHg, respectively) and the acrophase occurred between 16:00 and 17:45 h. This circadian variation is similar to that observed in cats, dogs and marmosets. The BP decreased during "behavioral sleep" (MBP down from 110 +/- 19 to 90 +/- 19 mmHg at 21:00 to 8:00 h). Both feeding and moving induced an increase in MBP (96 +/- 17 to 119 +/- 17 mmHg at 17:00 h and 97 +/- 19 to 105 +/- 12 mmHg at 15:00 h, respectively). The results show that conscious sloths present biphasic circadian fluctuations in BP levels, which are higher during the light period and are mainly synchronized with feeding.

Analysis of Variance↗
PubMed2003

Aerotolerance of human clinical isolates of Prevotella spp.

AIMS: To determine the influence of oxygen exposure and growth stages on oxygen tolerance for clinical and reference specimens of the genus Prevotella. METHODS AND RESULTS: Tolerance to oxygen exposure was evaluated along growth stages for a total of four Prevotella isolates constituted by two strains tested soon after isolation from periodontally compromised patients and two reference strains kept frozen (-86 degrees C) in our laboratory collection. Additionally, the recently recovered isolates were also assayed after 4 months exposed to oxygen during laboratory handling. On solid medium, recently recovered Prevotella specimens proved to be less tolerant to oxygen exposure soon after isolation than when exposed for 4 months to oxygen during laboratory handling. Oxygen resistance of reference strains maintained in the laboratory collection showed to be the highest when compared with the clinical isolates both before and after oxygen exposure. When oxygen tolerance was tested during growth, bacterial cells from the exponential phase were more tolerant. Differences were observed in protein patterns between clinical isolates soon after recovery and after laboratory handling as determined by SDS-PAGE of crude cell-free extracts. However, SOD activities were similar in all bacterial samples tested. CONCLUSIONS: The ability to adaptively change oxygen tolerance was observed for pathogenic specimens of Prevotella. This property may be considered a virulence factor. SIGNIFICANCE AND IMPACT OF THE STUDY: Adaptative aerotolerance of Prevotella as a factor for virulence and survival.

Adaptation, Physiological↗
PubMed1992

Effects of parathyroid hormone and calcium and their interrelationship on urinary acidification in the rat.

1. The influence of thyroparathyroidectomy on renal function and specifically on acid excretion was studied in rats with or without oral supplementation of calcium. 2. Thyroparathyroidectomy caused a significant decrease in glomerular filtration rate, in the urinary/plasma inulin ratio and in overall acid excretion. These changes were not corrected by calcium supplementation. 3. Rates of proximal tubular acidification were studied by means of double-barrelled resin/reference microelectrodes. Acidification half-time was significantly increased in both thyroparathyroidectomized and calcium-supplemented thyroparathyroidectomized rats (8.38 s and 7.40 s, respectively) compared with control rats (5.44 s). 4. When 10(-6) mol/l A23187, a calcium ionophore, was added to the luminal bicarbonate solution, the acidification half-time returned to 3.97 s in the thyroparathyroidectomized rats, whereas no significant changes were detected in the properties of acidification in the control rats. 5. These data show that parathyroid hormone and cellular calcium are important factors involved in proximal tubular H+ secretion, which appears to be largely dependent on a well-defined concentration range of these agents.

Animals↗
PubMed1991

Effect of aluminium on urinary acidification in the rat: influence of parathyroid hormone.

1. The influence of thyroparathyroidectomy and/or acidosis on renal function and specifically on acid excretion was studied in rats treated with a cumulative dose of 2 mg of aluminium. 2. Aluminium-treated and non-treated thyroparathyroidectomized rats showed a significant decrease in glomerular filtration rate and in the urinary/plasma inulin ratio without alteration in net acid excretion. 3. Non-treated thyroparathyroidectomized acidotic rats showed a significant fall in the amount of ammonium excreted and in overall acid excretion, suggesting that parathyroid hormone participates in an important way in the defence against metabolic acidosis. 4. The effects of acidosis, thyroparathyroidectomy and aluminium treatment on renal function parameters were not additive, suggesting a common final mechanism. In normal or acidotic aluminium-treated rats, thyroparathyroidectomy had no effect on renal acid excretion, suggesting that aluminium even in low doses inhibited the action of PTH on the renal tubule. 5. After exposure to aluminium, the relative inhibition of PTH on the renal tubule may become an additional factor that could contribute to the worsening of clinical conditions in which an inappropriate retention of acid loads can occur.

Acidosis↗
PubMed1988

Aminoglycoside and nephrotoxicity.

The effect of three aminoglycosides--gentamicin, netilmicin and amikacin--on renal acid excretion was studied in male rats treated with doses equivalent to those clinically used. The amikacin and netilmicin groups showed no important changes in the values of glomerular filtration rate (GFR), effective renal plasma flow (ERPF) and U/P inulin ratio during normal and acidotic conditions. The gentamicin group, however, showed a clear tendency to decreases in these functional parameters even in normal conditions, a finding that reinforces the concept that gentamicin is more nephrotoxic than other aminoglycosides. During normal conditions net acid excretion (BH) did not change with any of the three tested drugs. However, after an acute acid load BH markedly fell regardless of the antibiotic used. The capacity to elevate the urine-blood pCO2 was preserved after an alcaline overload, suggesting that the distal tubule was not significantly affected by aminoglycoside treatment. These data suggest that the clinical use of aminoglycosides during metabolic acidosis deserves close attention due to the possible deleterious effect that can emerge as the result of an inappropriate retention of acid loads.

Amikacin↗
PubMed1986

Effect of gentamicin on urinary acidification in the rat.

The effect of gentamicin, an aminoglycoside antibiotic, on renal function and especially on acid excretion was studied in normal and acidotic rats. The doses used were 1 (G4) and 10 (G40) times the suggested human therapeutic dose on a weight basis. After 10 days of each treatment, the glomerular filtration rate (GFR) was unchanged in G4 but fell significantly (p less than 0.05) in G40. In the acidotic groups (AG4 and AG40) there was an accentuated reduction in GFR, renal plasma flow and urine/plasma insulin ratio. Normal rats showed a normal acid excretion even with the high-dose treatment but, in the acidotic group, there was a significant decrease in ammonia excretion. The amount of bicarbonate excretion was significantly elevated in those groups, leading to a greater urinary pH. These results indicate that acute metabolic acidosis enhanced the nephrotoxic effects of gentamicin and impaired the excretion of an acid overload.

Ammonia↗
PubMed1985

Experimental guinea pig ocular infection by Salmonella typhimurium.

The clinical, microbiologic, and cytologic features of the guinea pig model of keratoconjunctivitis with enterobacteria, Salmonella typhimurium were elucidated. Guinea pig eyes were instilled with S. typhimurium and the eyes were studied by biomicroscopy, culture, cytology, pathology, and electron microscopy. All animals developed moderate to severe conjunctivitis that was present in 18% of the animals on day 1. It became more intense, appearing in all of the eyes on day 10 and disappeared before day 30. The cultures for S. typhimurium were almost all positive on days 1 and 2, declined steadily to 10% on day 10, and were negative after that. A coarse, epithelial punctate keratitis was present in more than 90% of the infected eyes at some time during the experiment. The keratitis had a biphasic clinical course. The first peak correlated with the maximum culture results, but during the second peak only 10% of the cultures were positive. Electron microscopy of the cornea showed the S. typhimurium at the epithelial surface within surface epithelial cells during the early phases of infection. The later phase keratitis, with negative culture results, resembles the keratitis of Reiter's syndrome.

Animals↗
PubMedDate not supplied

Effect of luminal calcium on proximal tubule bicarbonate reabsorption in the rat.

In previous investigations, it was found that rats depleted in parathyroid hormone (TPTX rats) had reduced rates of proximal bicarbonate reabsorption independent on blood calcium levels. In the present work, the role of calcium (Ca2+) in rat proximal tubule bicarbonate reabsorption was studied by in vivo stationary microperfusion. Tubules were perfused at different lumen Ca2+ concentrations in the presence and absence of the calcium ionophore A23187. Bicarbonate reabsorption was not affected by Ca2+ in the range of 0 to 1 mM, but was significantly reduced when 0.5 mM EGTA was added to the 0 Ca2+ perfusates, indicating that only at very low luminal Ca2+ levels, bicarbonate reabsorption ( = H+ secretion) was impaired. These observations indicate that Ca2+ in the tubule lumen is important for the maintenance of normal proximal bicarbonate transport, but the low Ca2+ level necessary to impair this transport mechanism is achieved only in the presence of EGTA, a condition that simulates the absence of parathyroid hormone.

Absorption↗