Mercury-induced vascular dysfunction is mediated by angiotensin II AT-1 receptor upregulation

Low doses of mercury (Hg) promote deleterious effects on cardiovascular system, but the mechanisms implicated remain unclear. This study analyzed whether angiotensin II AT-1 receptors are involved in the vascular dysfunction caused by chronic exposure to low HgCl₂ doses. For this, rats were divided into four groups and untreated (saline by im injections and tap water by gavage) or treated for 30 days as follows: Mercury (HgCl₂im, first dose of 4.6 µg kg^-1 and subsequent doses of 0.07 µg kg^-1 day^-1, and tap water by gavage); Losartan (saline im and losartan, 15 mg kg^-1 day^-1, by gavage); Losartan-Mercury (HgCl₂im and Losartan by gavage). Systolic blood pressure was measured by tail plethysmography, vascular reactivity in aorta by isolated organ bath, oxidative stress by measuring the levels of reactive oxygen species (ROS), malondialdehyde (MDA) and antioxidant capacity (FRAP) and protein expression of AT-1 receptors by Western Blot. As results, co-treatment with losartan prevented the increased aortic vasoconstrictor responses to phenylephrine (Phe), the involvement of ROS and prostanoids on the response to Phe and the reduced negative endothelial modulation by nitric oxide on these responses. Moreover, this co-treatment avoided the increase in plasmatic and vascular oxidative stress and AT-1 protein expression in aorta. In conclusion, these results suggest that AT-1 receptors upregulation might play a key role in the vascular damage induced by Hg exposure by increasing oxidative stress and probably by reducing NO bioavailability.