Acute cardiovascular toxicity of thallium (I) ions

The acute cardiovascular toxicity of thallium (I)-ions was studied in anesthetized rats and also in some isolated preparations. In pentobarbital-anesthetized rats, intravenously applied Tl2SO4 (range 3 to 100 mg/kg) caused a significant, dose-dependent decrease in mean arterial blood pressure and heart rate. In spontaneously beating guinea pig isolated atria, thallium (I)-ions (10(-5) to 10(-3) M) caused a concentration-dependent decrease in frequency, which was not influenced by atropine, cocaine, or by considerable changes in the potassium concentration of the medium. A direct influence of Tl+ on the sinus node is presumed. Thallium decreases contractile force probably as a result of its negative chronotropic properties, since the amplitude of contraction remained uninfluenced in electrically driven atria. Thallium (I)-ions were readily taken up by the guinea pig isolated atria. At a bath concentration of 5 times 10(-5) M Tl+ a tissue/medium ratio of approximately 45 was achieved. Probably, an exchange against cellular potassium takes place. Relaxation of vascular smooth muscle by Tl+ was demonstrated both in isolated aortic strips (rabbit) and in the isolated perfused rabbit ear preparation. Both the vascular smooth muscle relaxation and the decrease in heart rate would explain the acute hypotensive effect of thallium.