Efeitos da exposição crônica a baixas concentrações de cloreto de mercúrio (20 ηM) sobre o sistema cardiovascular de ratos

• Autor(a) principal: Giuberti, Karina
• Data de Publicação: 2010
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Espírito Santo (riUfes)
• Texto Completo: http://repositorio.ufes.br/handle/10/5172
• topic: ECA; Cloreto de mercúrio; Estresse oxidativo; Pressão arterial sistólica; Fisiologia; 612

Mercury is naturally present in earth's crust and it is inevitable, some degree of exposure during the whole life. It has been demonstrated a variety of pathological actions of mercury on the central nervous system, renal system and its association with increased cardiovascular risk. However, its toxic effects on the cardiovascular system under conditions of normotension and hypertension are not yet fully elucidated. In this study, Wistar and SHR rats (2.5 months old) were divided into four groups: control Wistar (Wistar CT) and control SHR (SHR CT) who received intramuscular injections of saline for 30 days or mercury (Hg Wistar) and (SHR Hg), which received 0.07 mg/kg/day HgCl2, the first dose was 4.6 mg/kg, reaching a final plasma concentration of about 29 ηM of mercury. At the end of treatment the following aspects were performed: assessment of weight, histological, hematological and biochemical profiles, measurements of hemodynamic parameters, angiotensin converting enzyme (ACE) activity and the production of malondealdeide (MDA) in the plasma of all animals. Chronic exposure to HgCl2 did not affect the weight and histological parameters when comparing Wistar CT vs Wistar Hg rats neither SHR CT compared to SHR Hg rats. In the hematological evaluation, the Wistar Hg rats showed a increased in platelet content (Wistar CT: 757 ± 55 vs Wistar Hg: 913 ± 20 103/µL) and neutrophils percentage (Wistar CT: 14 ± 5 vs Wistar Hg: 30 ± 4.3 %) and the percentage of lymphocytes decreased (Wistar CT: 83 ± 4.6 vs Wistar Hg: 68 ± 4.5 %), while in the SHR Hg, the percentage of neutrophils decreased (SHR CT: 45 ± 5.9 vs SHR Hg: 21.3 ± 4.8 %) and lymphocytes increased (SHR CT: 53 ± 6.5 vs SHR Hg: 76 ± 4.3 %). The glicemy values was increased in the Wistar Hg group (Wistar CT: 161.6 ± 12.3 vs Wistar Hg: 209 ± 15.4 mg/dL) meanwhile plasmatic globulin decreased (Wistar CT: 3.21 ± 0.09 vs Wistar Hg : 2.84 ± 0.1 g/dL). The systolic blood pressure, measured weekly by tail plethysmography, increased in rats in the fourth week of treatment (Wistar CT: 117 ± 3 vs Wistar Hg: 143 ± 5 mmHg). We also observed an increase in LV end-diastolic pressure of Wistar Hg rats (Wistar CT: 0.25 ± 0.4 vs Wistar Hg: 3.3 ± 0.5 mmHg). Treatment with Hg increased ACE activity in plasma (Wistar CT: 187.1 ± 16.2 vs Wistar Hg: 235.5 ± 14.2 ηmol/mL/min) and hearts of normotensive rats (Wistar CT: 3,4 ± 0.2 vs Wistar Hg: 4.1 ± 0.1 ηmol/mL/min/mg). In SHR Hg, ACE activity was increased in plasma (SHR CT: 113 ± 11.4 vs SHR Hg: 163 ± 15.8 ηmol/mL/min) and decreased in kidney (SHR CT: 80 ± 6.3 vs SHR Hg: 61.4 ± 2.8 ηmol/mL/min/mg), lung (SHR CT: 87.6 ± 2.2 vs SHR Hg: 75 ± 4 ηmol/mL/ min/mg), heart (SHR CT: 17.9 ± 1.1 vs SHR Hg: 14.8 ± 0.58 ηmol/mL/min/mg), brain (SHR CT: 40.3 ± 2.3 vs SHR Hg: 27.8 ± 1.8 ηmol/mL/min/mg) and aorta (SHR CT: 670 ± 16.3 vs SHR Hg: 535 ± 19.2 ηmol/mL/min/mg). The involvement of oxidative stress was assessed indirectly by measuring the production of MDA, which was found increased in the Wistar Hg rats in both plasma (Wistar CT: 0.93 ± 0.06 vs Wistar Hg: 1.28 ± 0.18 mM) and in heart (Wistar CT: 0.22 ± 0.01 vs Wistar Hg: 0.28 ± 0.01 mM) and decreased in the kidney (Wistar CT: 0.38 ± 0.03 vs Wistar Hg: 0.14 ± 0.01 mM). In SHR Hg rats, this production was increased in heart (SHR CT: 0.45 ± 0.02 vs SHR Hg: 0.55 ± 0.02 mM) and aorta (SHR CT: 0.96 ± 0.11 vs SHR Hg: 1.51 ± 0.14 mM) and decreased in the lungs (SHR CT: 0.21 ± 0.01 vs SHR Hg: 0.12 ± 0.01 mM), kidney (SHR CT: 0.96 ± 0.03 vs SHR Hg: 0.51 ± 0.01 mM) and brain (SHR CT: 0.54 ± 0.03 vs SHR Hg: 0.34 ± 0.01 mM). These results suggest that chronic exposure to mercury even at very low concentrations interferes with the activity of angiotensin converting enzyme and production of free radicals. Also it alters the levels of the blood glucose, platelet, immune, systolic blood pressure, and left ventricular end diastolic pressure. The results isolated or interconnected, can contribute to the understanding of various diseases related to contamination with metal. It can be conclude that such exposure represents a risk factor for developing of cardiovascular disease in normotensive animals (Wistar) and it may represents a aggregating factor of pre-existing risks to hypertensive rats (SHR).