Paula Frizera Vassallo

Toxic Effects of Mercury on the Cardiovascular and Central Nervous Systems

Environmental contamination has exposed humans to various metal agents, including mercury. This exposure is more common than expected, and the health consequences of such exposure remain unclear. For many years, mercury was used in a wide variety of human activities, and now, exposure to this metal from both natural and artificial sources is significantly increasing. Many studies show that high exposure to mercury induces changes in the central nervous system, potentially resulting in irritability, fatigue, behavioral changes, tremors, headaches, hearing and cognitive loss, dysarthria, incoordination, hallucinations, and death. In the cardiovascular system, mercury induces hypertension in humans and animals that has wide-ranging consequences, including alterations in endothelial function. The results described in this paper indicate that mercury exposure, even at low doses, affects endothelial and cardiovascular function. As a result, the reference values defining the limits for the absence of danger should be reduced.

Left and Right Ventricle Late Remodeling Following Myocardial Infarction in Rats

Background The mechanisms involved in cardiac remodeling in left (LV) and right ventricles (RV) after myocardial infarction (MI) are still unclear. We assayed factors involved in collagen turnover in both ventricles following MI in rats either presenting signs of heart failure (pulmonary congestion and increased LVEDP) or not (INF-HF or INF, respectively). Methods MI was induced in male rats by ligation of the left coronary artery. Four weeks after MI gene expression of collagen I, connective tissue growth factor (CTGF), transforming growth factor β (TGF-β) and lysyl oxidase (LOX), metalloproteinase-2 (MMP2) and tissue inhibitor metalloproteinase-2 (TIMP2) as well as cardiac hemodynamic in both ventricles were evaluated. Results Ventricular dilatation, hypertrophy and an increase in interstitial fibrosis and myocyte size were observed in the RV and LV from INF-HF animals, whereas only LV dilatation and fibrosis in RV was present in INF. The LV fibrosis in INF-HF was associated with higher mRNA of collagen I, CTGF, TGF-β and LOX expressions than in INF and SHAM animals, while MMP2/TIMP2 mRNA ratio did not change. RV fibrosis in INF and INF-HF groups was associated with an increase in LOX mRNA and a reduction in MMP2/TIMP2 ratio. CTGF mRNA was increased only in the INF-HF group. Conclusions INF and INF-HF animals presented different patterns of remodeling in both ventricles. In the INF-HF group, fibrosis seems to be consequence of collagen production in LV, and by reductions in collagen degradation in RV of both INF and INF-HF animals.

Effects of mercury on the arterial blood pressure of anesthetized rats

The available data suggests that hypotension caused by Hg2+ administration may be produced by a reduction of cardiac contractility or by cholinergic mechanisms. The hemodynamic effects of an intravenous injection of HgCl2 (5 mg/kg) were studied in anesthetized rats (N = 12) by monitoring left and right ventricular (LV and RV) systolic and diastolic pressures for 120 min. After HgCl2 administration the LV systolic pressure decreased only after 40 min (99 +/- 3.3 to 85 +/- 8.8 mmHg at 80 min). However, RV systolic pressure increased, initially slowly but faster after 30 min (25 +/- 1.8 to 42 +/- 1.6 mmHg at 80 min). Both right and left diastolic pressures increased after HgCl2 treatment, suggesting the development of diastolic ventricular dysfunction. Since HgCl2 could be increasing pulmonary vascular resistance, isolated lungs (N = 10) were perfused for 80 min with Krebs solution (continuous flow of 10 ml/min) containing or not 5 microM HgCl2. A continuous increase in pulmonary vascular resistance was observed, suggesting the direct effect of Hg2+ on the pulmonary vessels (12 +/- 0.4 to 29 +/- 3.2 mmHg at 30 min). To examine the interactions of Hg2+ and changes in cholinergic activity we analyzed the effects of acetylcholine (Ach) on mean arterial blood pressure (ABP) in anesthetized rats (N = 9) before and after Hg2+ treatment (5 mg/kg). Using the same amount and route used to study the hemodynamic effects we also examined the effects of Hg2+ administration on heart and plasma cholinesterase activity (N = 10). The in vivo hypotensive response to Ach (0.035 to 10.5 microg) was reduced after Hg2+ treatment. Cholinesterase activity (microM h-1 mg protein-1) increased in heart and plasma (32 and 65%, respectively) after Hg2+ treatment. In conclusion, the reduction in ABP produced by Hg2+ is not dependent on a putative increase in cholinergic activity. HgCl2 mainly affects cardiac function. The increased pulmonary vascular resistance and cardiac failure due to diastolic dysfunction of both ventricles are factors that might contribute to the reduction of cardiac output and the fall in arterial pressure.

Small doses of canrenone block the effects of ouabain on the mechanical activity of the heart and vessels of the rat.

Canrenone has been described as an antihypertensive drug that blocks endogenous ouabain effects in volume-dependent hypertensive models. Considering that some canrenone metabolites may be putative mutagenic factors, therapeutic dose reduction might be advantageous if the blockade of ouabain effects is maintained. In this study, the effects of low doses or concentrations of canrenone were investigated in rats by using isolated papillary muscles, Langendorff-perfused hearts, perfused rat-tail vascular bed, and anesthetized animals. Canrenone (0.5, 1, 2, and 5 mg/ml) produced a dose-dependent negative inotropic effect in papillary muscles contracting isometrically and blocked the positive inotropic effect produced by 660 microM ouabain. In Langendorff-perfused hearts beating spontaneously, a low concentration of canrenone (10 microg/ml) increased the isovolumic systolic pressure obtained at several diastolic pressures. Higher concentrations of canrenone (20, 30 microg/ml) brought the isovolumic pressure toward control values, and 100 microg/ml canrenone produced an isovolumic pressure reduction. In these preparations, 20 microg/ml canrenone reduced significantly the positive inotropic effects of 100 microM ouabain. Investigating the vascular smooth muscle reactivity to phenylephrine (PE; 0.5, 1, and 2 microg bolus injections) in the perfused rat-tail vascular bed, it was observed that canrenone blocked completely the enhancement of PE pressor effect produced by 1-h treatment with 100 microM ouabain. Similar results were obtained with the arterial blood pressure reactivity to PE in anesthetized rats. In these animals, canrenone (1 mg/kg) blocked the sensitizing effect of 18 microg/kg ouabain on PE reactivity. In conclusion, results presented here suggest that canrenone may block ouabain effects at very low concentrations. It blocked myocardial positive inotropic effects of ouabain on both papillary muscle and perfused hearts, and the sensitization of PE pressor effects. The results also suggest that canrenone at very small doses might be used to reduce arterial blood pressure in hypertensive conditions accompanied by increased ouabain plasma levels as the main therapeutic procedure or as an adjunct treatment to prevent ouabain sensitizing effects on pressor responses.

Renal Effects and Underlying Molecular Mechanisms of Long-Term Salt Content Diets in Spontaneously Hypertensive Rats.

Several evidences have shown that salt excess is an important determinant of cardiovascular and renal derangement in hypertension. The present study aimed to investigate the renal effects of chronic high or low salt intake in the context of hypertension and to elucidate the molecular mechanisms underlying such effects. To this end, newly weaned male SHR were fed with diets only differing in NaCl content: normal salt (NS: 0.3%), low salt (LS: 0.03%), and high salt diet (HS: 3%) until 7 months of age. Analysis of renal function, morphology, and evaluation of the expression of the main molecular components involved in the renal handling of albumin, including podocyte slit-diaphragm proteins and proximal tubule endocytic receptors were performed. The relationship between diets and the balance of the renal angiotensin-converting enzyme (ACE) and ACE2 enzymes was also examined. HS produced glomerular hypertrophy and decreased ACE2 and nephrin expressions, loss of morphological integrity of the podocyte processes, and increased proteinuria, characterized by loss of albumin and high molecular weight proteins. Conversely, severe hypertension was attenuated and renal dysfunction was prevented by LS since proteinuria was much lower than in the NS SHRs. This was associated with a decrease in kidney ACE/ACE2 protein and activity ratio and increased cubilin renal expression. Taken together, these results suggest that LS attenuates hypertension progression in SHRs and preserves renal function. The mechanisms partially explaining these findings include modulation of the intrarenal ACE/ACE2 balance and the increased cubilin expression. Importantly, HS worsens hypertensive kidney injury and decreases the expression nephrin, a key component of the slit diaphragm.

SERCA-2a is involved in the right ventricular function following myocardial infarction in rats.

AIMS Right ventricular (RV) function is considered an independent predictor of mortality and development of heart failure (HF) in patients with left ventricle dysfunction following myocardial infarction (MI). The functional and molecular mechanisms that may explain the RV dysfunction are still poorly understood. Our study was conducted to investigate RV contractility and the myocardium protein involved in the calcium handling following MI in rats. MAIN METHODS MI was surgically induced in male Wistar rats to create transmural infarctions involving 40-60% of the left ventricle surface. Infarcted rats were divided into two groups: those that presented classical signs of congestive heart failure (HF group) and those that did not (INF group), and compared to control animals (Sham). RV contractility was studied using isometric contraction in isolated strips and isovolumetric pressure in isolated heart. KEY FINDINGS Inotropic responses in RV strips were preserved in the INF group but were reduced in the HF group (3.75 mM Ca(2+) treatment: Sham = 163 ± 18; INF = 148 ± 19; HF = 68 ± 11 g/g*; *p < 0.05; 5 × 10(-5) M isoproterenol: Sham = 151 ± 15, INF = 134 ± 17, HF = 52 ± 7 g/g*; *p < 0.05). An increase in SERCA-2a protein expression in the RV was observed in the INF group but not in the HF group, which could explain the preserved inotropic response in these animals. SIGNIFICANCE Increased SERCA-2a protein expression may play a role in the preservation of RV function post-MI. Therefore, therapeutic strategies that attempt to increase SERCA protein expression levels may be useful for the treatment of HF.

The left ventricular contractility of the rat heart is modulated by changes in flow and alpha 1-adrenoceptor stimulation.

Myocardial contractility depends on several mechanisms such as coronary perfusion pressure (CPP) and flow as well as on alpha 1-adrenoceptor stimulation. Both effects occur during the sympathetic stimulation mediated by norepinephrine. Norepinephrine increases force development in the heart and produces vasoconstriction increasing arterial pressure and, in turn, CPP. The contribution of each of these factors to the increase in myocardial performance needs to be clarified. Thus, in the present study we used two protocols: in the first we measured mean arterial pressure, left ventricular pressure and rate of rise of left ventricular pressure development in anesthetized rats (N = 10) submitted to phenylephrine (PE) stimulation before and after propranolol plus atropine treatment. These observations showed that in vivo alpha 1-adrenergic stimulation increases left ventricular developed pressure (P < 0.05) together with arterial blood pressure (P < 0.05). In the second protocol, we measured left ventricular isovolumic systolic pressure (ISP) and CPP in Langendorff constant flow-perfused hearts. The hearts (N = 7) were perfused with increasing flow rates under control conditions and PE or PE + nitroprusside (NP). Both CPP and ISP increased (P < 0.01) as a function of flow. CPP changes were not affected by drug treatment but ISP increased (P < 0.01). The largest ISP increase was obtained with PE + NP treatment (P < 0.01). The results suggest that both mechanisms, i.e., direct stimulation of myocardial alpha 1-adrenoceptors and increased flow, increased cardiac performance acting simultaneously and synergistically.

Chronic Exposure to Low Doses of HgCl2 Avoids Calcium Handling Impairment in the Right Ventricle after Myocardial Infarction in Rats

Right ventricle systolic dysfunction is a major risk factor for death and heart failure after myocardial infarction (MI). Heavy metal exposure has been associated with the development of several cardiovascular diseases, such as MI. The aim of this study was to investigate whether chronic exposure to low doses of mercury chloride (HgCl2) enhances the functional deterioration of right ventricle strips after MI. Male Wistar rats were divided into four groups: Control (vehicle); HgCl2 (exposure during 4 weeks- 1st dose 4.6 µg/kg, subsequent dose 0.07 µg/kg/day, i.m. to cover daily loss); MI surgery induced and HgCl2-MI groups. One week after MI, the morphological and hemodynamic measurements and isometric tension of right ventricle strips were investigated. The chronic HgCl2 exposure did not worsen the injury compared with MI alone in the morphological or hemodynamic parameters evaluated. At basal conditions, despite similar maximum isometric force at L-max, relaxation time was increased in the MI group but unaffected in the HgCl2-MI compared to the Control group. Impairment of the sarcoplasmic reticulum (SR) function and reduction in the sarcolemmal calcium influx were observed in MI group associated with SERCA2a reduction and increased PLB protein expression. Induction of MI in chronic HgCl2 exposed rats did not cause any alteration in the developed force at L-max, lusitropic function or −dF/dt except for a tendency of a reduction SR function. These findings could be partially explained by the normalization in the sarcolemmal calcium influx and the increase in NCX protein expression observed only in this group. These results suggest that chronic exposure to low doses of HgCl2 prevents the impaired SR function and the reduced sarcolemmal calcium influx observed in MI likely by acting on NCX, PLB and SERCA2a protein expression.

Low-salt diet increases NO bioavailability and COX-2 vasoconstrictor prostanoid production in spontaneously hypertensive rats.

AIMS The ability of dietary sodium restriction to reduce the incidence of cardiovascular mortality and improve vascular function in hypertension still remains poorly understood. The aim of this study was to observe the effects of a long period of salt restriction on the vascular reactivity of mesenteric resistance arteries of SHRs. METHODS Male SHRs received either standard-salt diet (0.3% NaCl) or low-salt diet (0.03% NaCl) for 28weeks. Vascular reactivity was studied in mesenteric artery segments and the influence of cyclooxygenase-2 (COX-2), reactive oxygen species (ROS) and participation of the renin-angiotensin system were analyzed. KEY FINDINGS Decreased salt intake did not affect phenylephrine-induced vasoconstriction but increased acetylcholine-induced vasodilatation and also increased the response to phenylephrine after inhibition of NO synthase by L-NAME (100μM) and iNOS protein expression was elevated. Cyclooxygenase inhibitor indomethacin (10μM) and COX-2 inhibitor NS 398 (1μM) decreased the reactivity to phenylephrine in low-salt-treated group, and COX-2 protein expression was elevated in low-salt group. The effects of apocynin (10μM); superoxide anion scavenger, tiron (1mM); hydrogen peroxide scavenger, catalase (1000UmL(-1)); and ACE and AT1 receptor blockers, enalapril (10μM) and losartan (10μM) on vascular reactivity were not different between two groups. The levels of AT1 protein expression were similar in both groups. SIGNIFICANCE Low-salt diet modulates mesenteric vascular responses via increased NO bioavailability suggested by increased iNOS protein expression and vasoconstrictor prostanoid production via COX-2 pathway, in SHRs. Neither ROS nor the local renin-angiotensin system is involved in these responses.

Blood flow restriction attenuates eccentric exercise‐induced muscle damage without perceptual and cardiovascular overload

The aim of this study was to evaluate the acute effects of high‐intensity eccentric exercise (HI‐ECC) combined with blood flow restriction (BFR) on muscle damage markers, and perceptual and cardiovascular responses. Nine healthy men (26 ± 1 years, BMI 24 ± 1 kg m−²) underwent unilateral elbow extension in two conditions: without (HI‐ECC) and with BFR (HI‐ECC+BFR). The HI‐ECC protocol corresponded to three sets of 10 repetitions with 130% of maximal strength (1RM). The ratings of perceived exertion (RPE) and pain (RPP) were measured after each set. Muscle damage was evaluated by range of motion (ROM), upper arm circumference (CIR) and muscle soreness using a visual analogue scale at different moments (pre‐exercise, immediately after, 24 and 48 h postexercise). Systolic (SBP), diastolic (DBP), mean blood pressure (MBP) and heart rate (HR) were measured before exercise and after each set. RPP was higher in HI‐ECC+BFR than in HI‐ECC after each set. Range of motion decreased postexercise in both conditions; however, in HI‐ECC+BFR group, it returned to pre‐exercise condition earlier (post‐24 h) than HI‐ECC (post‐48 h). CIR increased only in HI‐ECC, while no difference was observed in HI‐ECC+BFR condition. Regarding cardiovascular responses, MBP and SBP did not change at any moment. HR showed similar increases in both conditions during exercise while DBP decreased only in HI‐ECC condition. Thus, BFR attenuated HI‐ECC‐induced muscle damage and there was no increase in cardiovascular responses.