Small doses of mercury increase arterial pressure reactivity to phenylephrine in rats

Mercury reduces cardiac contractility and arterial pressure at micromolar concentrations. We investigated the actions of 680 ng/kg HgCl2 on arterial pressure, heart rate (HR) and on the pressor reactivity to phenylephrine (PHE) in rats before and 1 h after HgCl2 administration and after hexametonium, verapamil and tempol treatments. HgCl2 increased baseline systolic (SAP) and diastolic pressure (DAP) and HR, sensitivity (pD2) and maximal response (Emax) to PHE pressor reactivity. Hexametonium and verapamil reduced baseline pressures and HR that increased after HgCl2 treatment. Hexametonium did not change pD2 or Emax to PHE but verapamil reduced them. These parameters increased after HgCl2 administration. Tempol did not alter baseline pressures, HR or PHE reactivity before and after HgCl2. Results suggest that HgCl2 increases SAP, DAP, HR and PHE reactivity; autonomic reflexes reduces HgCl2 action; baseline pressure level do not interfere on HgCl2 pressor effects but free radicals seems to be involved.