Thyroid hormones mediated effect of insulin on alloxan diabetic rat atria

1. The influence of alloxan-induced diabetes was studied on spontaneously beating rat atria. Diabetic atria were found to have decreased rates, increased contractility and decreased responsiveness to both inotropic and chronotropic effects of isoprenaline. 2. Thyroid hormone levels were significantly reduced in diabetic animals. This revealed that the decrease in atrial beta-adrenergic responses was associated with a reduction in serum levels of thyroid hormones. 3. Insulin treatment of diabetic rats for 10 days corrected the changes observed in diabetic atria. Serum levels of thyroid hormones returned to normal following insulin treatment as well. 4. Administration of insulin to thyroidectomized-diabetic rats did not reverse the diabetes-induced changes suggesting that thyroid hormones are needed for insulin to normalize the alterations observed in diabetic atria.