Mechanisms in cardiovascular regulation following chronic exposure of male rats to inorganic mercury.

In this study we verified the possibility that chronic exposure to inorganic mercury may induce hemodynamic changes in the rat by affecting some neurogenic and/or humoral mechanisms regulating cardiovascular function. For this reason, aortic blood pressure, maximum rate of rise of the left ventricular pressure, heart rate, and electrocardiogram were monitored under pentothal anesthesia in rats which received 50 micrograms/ml of mercury (as HgCL2) in drinking water for 320 days and in control rats. No pressor or electrocardiographic changes were found in mercury-treated animals, which showed increase of cardiac inotropism and decrease of the pressor and inotropic responses to bilateral carotid occlusion. Cardiovascular responses to bilateral vagotomy and iv hexamethonium under vagotomy were unchanged in the mercury-exposed rats. In these animals both pressor and inotropic responses to iv norepinephrine and to higher doses of epinephrine were reduced, while the vascular beta-adrenergic response to 0.125 micrograms/kg of iv epinephrine was potentiated. Cardiovascular responses to acetylcholine, angiotensin I, angiotensin II, bradykinin, histamine, and serotonin did not differ in the two groups of rats. These results indicated that chronic mercury exposure affects cardiovascular function by interfering with the baroreflex mechanisms and/or the reactivity to catecholamines. Higher amounts of mercury were found in kidney, but the metal was significantly accumulated also in urine, blood, and brain. Mercury exposure greatly increased the levels of copper and zinc, but not that of iron, in brain and kidney. The increased accumulation of copper and zinc in tissues may be related in part to the mercury-induced synthesis of metallothionein, a protein able to bind these essential metals. It may be suggested that zinc and copper interact with mercury in inducing cardiovascular changes.