Chronic HgCl(2) treatment increases vasoconstriction induced by electrical field stimulation: role of adrenergic and nitrergic innervation.

In the present study, we have investigated the possible changes in rat mesenteric artery vascular innervation function caused by chronic exposure to low doses of HgCl(2) (mercuric chloride), as well as the mechanisms involved. Rats were divided into two groups: (i) control, and (ii) HgCl(2)-treated rats (30 days; first dose, 4.6 µg/kg of body weight; subsequent dose, 0.07 µg·kg-1 of body weight·day-1, intramuscularly). Vasomotor response to EFS (electrical field stimulation), NA (noradrenaline) and the NO donor DEA-NO (diethylamine NONOate) were studied, nNOS (neuronal NO synthase) and phospho-nNOS protein expression were analysed, and NO, O(2)- (superoxide anion) and NA release were also determined. EFS-induced contraction was higher in the HgCl(2)-treated group. Phentolamine (1 µmol/l) decreased the response to EFS to a greater extent in HgCl(2)-treated rats. HgCl(2) treatment increased vasoconstrictor response to exogenous NA and NA release. L-NAME (N(G)-nitro-L-arginine methyl ester; 0.1 mmol/l) increased the response to EFS in both experimental groups, but the increase was greater in segments from control animals. HgCl(2) treatment decreased NO release and increased O(2)- production. Vasodilator response to DEA-NO was lower in HgCl(2)-treated animals. Tempol increased DEA-NO-induced relaxation to a greater extent in HgCl(2)-treated animals. nNOS expression was similar in arteries from both experimental groups, whereas phospho-nNOS was decreased in segments from HgCl(2)-treated animals. HgCl(2) treatment increased vasoconstrictor response to EFS as a result of, in part, reduced NO bioavailability and increased adrenergic function. These findings offer further evidence that mercury, even at low concentrations, is an environmental risk factor for cardiovascular disease.