Abstract
Summary
The influence of thyroxine administration and thyroidectomy on the contractility of the myocardium and its responsiveness to ouabain was evaluated in rats. Electrically driven strips of right ventricle, isolated from rats treated for 36 days with thyroxine, contracted with less than 50% of the force of strips (under comparable conditions) removed from normal animals. Ventricle strips removed from rats 58 days after thyroidectomy contracted with greater force than those of normal hearts. Ouabain, 1 μg/ml, increased contractile force in all groups, but the total increase was less in both the thyroxine-treated group and thyroidectomized group than in the control. No explanation can be offered for the altered contractility and responsiveness of myocardium produced by excess thyroxine and by ablation of the thyroid gland.
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