Role of Adrenal in Uptake of I 131 by the Thyroid Following Parenteral Administration of Epinephrine

Abstract

In a previous paper 1 we reported that the parenteral injection of epinephrine into both the intact and the totally thyroidectomized dog resulted in an increase in secretion of thyrotropin from the adenohypophysis. In the intact dog this was evidenced by the development of hyperplastic changes in the thyroid following the daily injection of adrenalin-in-oil. Serum obtained from similarly treated totally thyroidectomized animals, when injected subcutaneously into young guinea pigs not exceeding 200 g in weight, resulted in hyperplastic changes in the thyroids of the treated guinea pigs.

It was further reported that the increase in circulating thyrotropic factor resulting from the injection of epinephrine in totally thyroidectomized dogs reached its peak approximately 4 to 6 days following the beginning of treatment, and thereafter began to diminish despite the continued injection of epinephrine.

The present report is concerned with a study of the role of the adrenals in the above described phenomena. In place of the biological assay method previously employed for the determination of circulating thyrotropin, we used the percentage uptake of parentally administered I131 as an index of thyroid activity. This technique has the relative advantages of simplicity and a higher degree of accuracy over the biological assay method.

Methods. Male rats of the Wistar strain (Carworth Farms) weighing approximately 125 g were employed. They were placed on a low iodine, minimally goitrogenic (Steenboch) diet∗ for at least 3 weeks before being used experimentally in order to insure an adequate uptake by the thyroid gland of I¹³¹. 2 In the adrenalectomy experiments, rats of the Sprague-Dawley strain were also employed because of the reported lesser frequency of accessory adrenal tissue.

The experiments were planned to study the 24-hour percentage uptake of parenterally administered I131 by the thyroid gland after the administration of epinephrine in the intact and in the adrenalectomized animals.