Suppression of thyroid function by pituitary tumor MtTW5.

Abstract

A transplantable pituitary tumor, MtTW5, which secretes prolactin and growth hormone but no TSH or ACTH, causes a marked increase in total body weight and in the weight of most internal organs. However, the pituitary glands of tumor-bearing rats weighed significantly less in proportion to body weight than did pituitaries in control rats. Incorporation of 131I into the trichloroacetic acid-soluble and the protein fractions of the thyroid and serum was measured. Less 131I was incorporated into these fractions of the thyroid and into the protein fraction of serum of tumor-bearing rats than in control rats. These results were obtained in intact female, spayed female, nephrectomized female and male rats. After acute treatment with propylthiouracil, tumor-bearing rats incorporated less 131I into their thyroids than did controls similarly treated with propylthiouracil. Thus, the primary defect in the thyroid of tumorbearing rats is in its inability to concentrate iodine from the blood. Histological examination o...