It has been proposed that angiotensin II

It has been proposed that angiotensin II (Ang II) may upregulate COX-2 expression and the subsequent vasoconstrictor prostanoids production through the activation of AT-1 receptors in vascular smooth muscle cells (Hu et al., 2002). Additionally, this peptide is also able to stimulate the generation of superoxide anion by increasing the NADPH oxidase activity in vascular smooth muscle cells from normotensive rats (Griendling et al., 1994, Garcia-Redondo et al., 2016) and in hypertension models (Rajagopalan et al., 1996, Touyz et al., 2005, Martinez-Revelles et al., 2013). However, the role of Ang II on the activation of ROS and COX-2 pathways and the associated vascular alterations in the Ouabain receptor during exposure to Hg is still unclear. The purpose of the study was to investigate the role of Ang II AT-1 receptors in the vascular damage caused by chronic exposure to HgCl2 at low doses and to clarify the possible interactions between ROS and COX-2 pathways in this damage.
Material and methods
Results The water and food intake did not differ between the groups during the treatment (data not shown). Moreover, no differences in body weight gain were observed between the groups before and after the treatment (body weight gain, in g: Untreated: 66.3 ± 14.1; HgCl2: 68.7 ± 23.8; Los: 70.4 ± 9.6; LosHg: 70.0 ± 23.8; n = 8; P> .05). As previously shown (Peçanha et al., 2010; Rizzetti et al., 2013; Rizzetti et al., 2017), the SBP remained unchanged at the end of Hg treatment (in mmHg: Untreated: 118.7 ± 0.9; HgCl2: 118.7 ± 1.5, n = 5; P> .05); losartan-treated rats had also similar blood pressure levels (Los: 118.2 ± 1.6; LosHg: 112.5 ± 1.1; n = 5; P> .05) (Fig. 1). As previously described (Peçanha et al., 2010), treatment with HgCl2 for 30 days did not alter the vascular integrity, measured by the response to KCl (Untreated: 1.97 g ± 0.09; HgCl2: 1.93 ± 0.05; n = 8; P> .05), while it reduced the endothelium-dependent vasodilator response to ACh without affecting the endothelium-independent vasodilator response to SNP and increased the contractile response to Phe in aortic segments (Fig. 2A-C). Treatment with losartan did not affect response to KCl (Los: 1.70 ± 0.1; LosHg: 1.80 ± 0.1; n = 8; P > .05); interestingly, co-treatment prevented the reduction in the ACh-induced relaxation as well as the increased vasoconstrictor response to Phe (Fig. 2A,C). Endothelium removal or the incubation with the NOS inhibitor L-NAME caused a significant increase in the contractile response to Phe (Figs. 3A,B and 4A,B), although this increase was lower in aorta from animals exposed to HgCl2, as demonstrated by dAUC values (Figs. 3E and 4E). Losartan treatment did not modify the effect of both endothelium removal or L-NAME; thus, aortic segments from animals that received treatment with losartan in combination with HgCl2 showed similar effects of endothelium removal or L-NAME to the Untreated group (Figs. 3C,D and 4C,D), suggesting that AT-1 receptors are implicated in the reduction of the endothelial modulation by NO of contractile response to Phe induced by the metal. Both the NADPH oxidase inhibitor apocynin and the superoxide anion scavenger SOD reduced the contractile response to Phe in aorta from untreated and Hg-treated rats (Figs. 5A,B and 6A,B); however, this reduction was greater in aorta of animals treated with HgCl2, as evidenced by dAUC values (Figs. 5E and 6E). Losartan prevented the increased ROS participation on contractile response to Phe; thus, the effect of both apocynin and SOD on the vasoconstrictor responses to Phe was abolished in the groups receiving losartan alone or associated with HgCl2 (Figs. 5C,D and 6C,D). Biochemical data also demonstrated the effect of losartan on HgCl2-induced oxidative stress. Thus, the co-treatment with losartan prevented the increase in the ROS levels, normalized the antioxidant capacity in plasma and aorta and prevented the lipid peroxidation in plasma of HgCl2-treated rats (Fig. 7, Fig. 8).