EFFECT OF NEONATAL HYPERTHYROIDISM ON PITUITARY STRUCTURE AND FUNCTION IN THE RAT

Abstract

SUMMARY: 1. Infant rats were given doses of l-triiodothyronine (T₃) alone and combined with growth hormone during different periods of development. The effects of these treatments on the growth of the body and on the size and structure of the pituitary and thyroid glands have been examined. 2. At the dose levels given, the growth of the body and of the thyroid and pituitary glands was impaired. This impairment persisted in rats treated during the first 24 days of life and in animals in which treatment was confined to the 2–4th days long after injections had been discontinued and well into adult life. It did not persist in rats in which treatment was begun after the 14th day of age. 3. There were no obvious structural changes in the thyroid gland apart from its reduced size. All treatments were followed by pituitary changes characterized by a severe reduction, both in relative and absolute amount, of acidophilic tissue. There was only minor restoration of these changes after discontinuation of the hormone treatment except in rats injected after the 14th day in which recovery was complete. Changes in the amount of mucoid tissue (PAS-positive cells) were variable and generally of doubtful statistical significance. Non-secretory tissue was unaffected. 4. Administration of growth hormone in combination with T₃ for the first 24 days of life did not give rise to effects which were noticeably different from those of giving T₃ alone over the same period. 5. Possible explanations for these findings and the interrelationship between the pituitary changes and impaired growth are discussed.