Mechanisms of cardiovascular regulation in male rabbits chronically exposed to cadmium.

Male rabbits received 20 micrograms/ml of cadmium in drinking water for nine months. At the end of the treatment aortic vascular resistance was increased, whereas maximum rate of increase in left ventricular pressure, aortic blood flow, stroke volume, cardiac output, left ventricular minute work, and left ventricular stroke work were reduced. Arterial blood pressure, heart rate, and the index of myocardial oxygen consumption were not modified. The exposed rabbits also showed reduced pressor responses to vagotomy, increased cardiovascular responses to angiotensin I and II and isoprenaline, and lower responses to serotonin and guanethidine; the bradycardia induced by clonidine was augmented; the cardiovascular effects of bilateral carotid occlusion, hexamethonium, phenylephrine, histamine, acetylcholine, tyramine, papaverine and verapamil were unaltered. In the treated rabbits cadmium was appreciably higher in the kidney than in the heart; however, renal concentrations of cadmium were lower than those reported as critical for workers exposed to cadmium. Zinc was increased in the kidney but not in the heart, whereas copper remained unchanged in the examined organs. In rabbits treated with cadmium the increased aortic vascular resistance and the reduced myocardial contractility contribute to preserve a haemodynamic equilibrium without alteration of blood pressure and heart rate; the question of whether a similar condition may be present in people exposed to cadmium with normal cardiovascular parameters is discussed.