Abstract
Summary
The correlation between the suppression of thyroidal uptake of radioactive iodide and the serum percent free thyroxine (PFT) in rats with hormone-secreting pituitary tumors was studied. Thyroid glands in intact male or female rats bearing the pituitary tumor 7315a, which secretes prolactin and ACTH, took up 30 and 34% of Na131 I as compared with nontumor intact controls. The serum PFT of these tumor-bearing rats was 72% higher than controls. Adrenalectomy resulted in complete restoration of thyroidal function to normal levels and was accompanied by a fall in serum PFT. Serum PFT was significantly decreased in the sera of adrenalectomized nontumor-bearing rats compared with intact controls, and this decrease was prevented by predniso-lone treatment. The PFT in sera of predniso-lone-treated adrenalectomized rats was not significantly different from intact controls. It is suggested that in the 7315a tumor-bearing animals the decreased thyroid function is related to the increase in serum PFT. This increase in PFT may reflect a decrease in total binding of thyroxine to serum proteins and this effect may be mediated by the elevated serum corticosteroids caused by the ACTH secreted by the pituitary tumor.
Get full access to this article
View all access options for this article.