Chronic mercury exposure impairs the sympathovagal control of the rat heart

Abstract

Mercury is known to cause harmful neural effects affecting the cardiovascular system. Here, we evaluated the chronic effects of low-dose mercury exposure on the autonomic control of the cardiovascular system. Wistar rats were treated for 30 days with HgCl (1st dose 4.6 μg/kg followed by 0.07 μg/kg per day, intramuscular) or saline. The femoral artery and vein were then cannulated for evaluation of autonomic control of the hemodynamic function, which was evaluated in awake rats. The following tests were performed: baroreflex sensitivity, Von Bezold-Jarisch reflex, heart rate variability (HRV) and pharmacological blockade with methylatropine and atenolol to test the autonomic tone of the heart. Exposure to HgCl for 30 days slightly increased the mean arterial pressure and heart rate (HR). There was a significant reduction in the baroreflex gain of animals exposed to HgCl . Moreover, haemodynamic responses to the activation of the Von Bezold-Jarisch reflex were also reduced. The changes in the spectral analysis of HRV suggested a shift in the sympathovagal balance toward a sympathetic predominance after mercury exposure, which was confirmed by autonomic pharmacological blockade in the HgCl group. This group also exhibited reduced intrinsic HR after the double block suggesting that the pacemaker activity of the sinus node was also affected. These findings suggested that the autonomic modulation of the heart was significantly altered by chronic mercury exposure, thus reinforcing that even at low concentrations such exposure might be associated with increased cardiovascular risk.

Mercury Biodistribution in Rats after Chronic Exposure to Mercury Chloride

“…20,44 Notwithstanding, our group have previously described cardiac dysfunction even in those rats chronically injected with lower doses. 11,20 The reason for this inconsistency between the evidence of cardiac dysfunction even at doses that do not lead to detectable accumulation in the heart has yet to be studied.…”

“…In this regard, it has been identified harmful effects to the nervous, cardiovascular renal and other systems. 4,5,[9][10][11][12][13] About the distribution of mercury among the organs and tissues, it was demonstrated that once organic mercury is absorbed, it is almost totally oxidized to the divalent form (inorganic mercury) in erythrocytes, liver and kidneys.…”

The effect of polyunsaturated fatty acids on cardiovascular risk factors and urinary mercury in workers employed at electrolytic production of chlorine

“…Stages as in Table 3. Statistically significant differences between the Hg-U measured at stages I and II: * p < 0.05; *** p < 0.001. ganic mercury [18]. However, the results of other studies on adults with environmental exposure to mercury were heterogeneous and did not show any consistent associations between mercury concentrations and cardiac autonomic function [19].…”

Impaired participation of potassium channels and Na+/K+‐ATPase in vasodilatation due to reduced nitric oxide bioavailability in rats exposed to mercury

“… Nevertheless, the blood pressure or cardiac haemodynamics of these animals remained unchanged despite endothelial dysfunction. In fact, experimental studies have been unable to recapitulate hypertension in an animal model when varying doses , but indicated a time‐dependent effect of mercury on the blood pressure …”