Lead and mercury 28 day exposure at small concentrations reduces smooth muscle relaxation by decreasing cGMP

Cardiovascular diseases are among the main causes of mortality in the world. There is evidence of cardiovascular harm after exposure to low lead or mercury concentrations, but the effects of chronic exposure to the association of low doses of these toxic metals are still unknown. This work evaluated after 4 weeks, the association effects of low concentrations of lead and mercury on blood pressure and vascular resistance reactivity. Wistar rats were exposed for 28 days to lead acetate (1st dose of 4 μg/100 g and subsequent doses of 0.05 μg /100 g/day to cover daily losses) and mercury chloride (1st dose of 2.17 μg/kg and subsequent doses of 0.03 μg/kg/ day to cover daily losses) and the control group received saline, i.m. Results showed that treatment increased blood pressure and induced left ventricular hypertrophy. The mesenteric vascular reactivity to phenylephrine and the endothelium-dependent vasodilator response assessed by acetylcholine did not change. Additionally, reduced involvement of vasoconstrictor prostanoids derived from cyclooxygenase was observed in the PbHg group. By other regulatory routes, such as potassium channels, the vessel showed a greater participation of BK_Ca channels, and a reduction in the participation of K_v channels and SK_Ca channels. The endothelium-independent smooth muscle relaxation was significantly impaired by reducing cGMP, possibly through the hyperstimulation of Phosphodiesterase-5 (PDE5). Our results suggested that exposure to low doses of lead and mercury triggers this compensatory mechanism, in response to the augment of arterial pressure.