THE EFFECT OF GOITROGEN WITHDRAWAL ON THE PITUITARY-THYROID SYSTEM OF THE GUINEA PIG1

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Abstract
There pituitary-thyroid system following the extensive changes induced in these glands by the administration of anti-thyroid agents. Morphologic alterations are known to persist in the thyroid of various species long after goitrogen withdrawal (Astwood, Sullivan, Bissell, and Tyslowitz, 1943; Mackenzie and Mackenzie, 1944; Engle and Aranov, 1946; Webster, 1949) but the status of thyroid and pituitary function under these conditions has received scant attention. There are certain indications that restoration of the normal pituitary-thyroid balance after thyroid inhibition may be characterized by an initial period of temporarily enhanced function. D’Angelo, Paschkis, Cantarow, Siegel, and Rivero Fontan (1951) have demonstrated in guinea pigs treated for prolonged periods with propylthiouracil (PTU), that depressed thryoid uptakes of I131 quickly rebound above the normal range after goitrogen withdrawal and that increased radioactivity in such glands reflects not only increased tissue mass but also augmented avidity for radioiodine (“rebound phenomenon”).