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Formation of Adenomata in Hypophyses of Rats Subjected to both Subtotal Thyroidectomy and Administration of ¹³¹I, and its Prevention by Feeding of Desiccated Thyroid¹

Department of Physiology, University of California, Berkeley, California

The tumorigenic effect of subtotal thyroidectomy on the pituitary was studied in 212 Long-Evans female rats. Of the 133 pituitaries that contained adenomata after 2 years, 76% were of the thyrotropic cell type. This finding confirms earlier work on the effect of long-term thyroxine deficiency.

The feeding of desiccated thyroid reduced the percentages of thyrotropic cell adenomata from a mean of 60 to a mean of 33. Thyroid feeding reduced the percentages of all adenomata from a mean of 72 to a mean of 53.

A single administration of 1 µc of ¹³¹I did not increase the number of, or tendency towards, anaplastic changes in pituitary adenomata of subtotally thyroidectomized rats fed a stock diet. The same dose of ¹³¹I did not increase the incidence of pituitary adenomata in unoperated animals fed either the stock diet or the stock diet supplemented with desiccated thyroid. Two rats that developed malignant thyroid carcinomata after receiving 1 µc of ¹³¹I did not show cell changes or adenomata in the pituitary. The absence of cytologic signs of thyroxine deficiency in the pituitary cells of these rats supports the view that irradiation per se might well have been the cause of the neoplasms found in their thyroid glands.

The pituitary adenomata found in 124 unoperated rats, treated in the same way as the subtotally thyroidectomized groups with respect to ¹³¹I dosage and thyroid feeding, closely resembled those found in the normal control group in number as well as in cell type.

¹ This work was supported by a contract from the United States Atomic Energy Commission (UCB-34P11-3).

² Department of Endocrinology, Medical Research Council, Dunedin, New Zealand.

³ Department of Medicine, Permanente Medical Group and Kaiser Foundation Hospital, Oakland, California.

Received 3/ 4/65. Revised 6/ 7/65.