PHYSIOLOGY OF RADIATION INJURY 993 



apparently not due to damage of the thyroid, esophagus, or pituitary, 

 nor is it related to changes in the blood. Complications have also been 

 observed clinically after excessive irradiation of the thyroid area (Lukens, 

 1948). 



The avidity of the thyroid for iodine and the availability of radio- 

 iodine have greatly facilitated the study of thyroid sensitivity. The 

 results of such investigations reveal, in general, that relatively large 

 amounts of radioiodine as equivalent roentgens are required to embarrass 

 thyroid function (Findlay and Leblond, 1948; Feller et al, 1949; Skanse, 

 1948; Gorbman, 1949; Goldberg, Chaikoff, et al, 1950). Partial destruc- 

 tion of the thyroid with colloid degeneration has been seen in rats 6 days 

 after injection of approximately 70 /xc of I 131 , at which time about 20,000 

 rep had been delivered to the gland (Findlay and Leblond, 1948). Thy- 

 roid function as indicated by the chemical iodine content of the gland, its 

 retention of radioiodine, and the level of plasma iodine is not disturbed 

 after injection of 30 fxc of I 131 in the rat (Feller et al, 1949). Weight of 

 the chick thyroid may be decreased 16 days after administration of only 

 10 /xc, but even this tracer dose is equivalent to approximately 15,000 rep 

 in terms of thyroid irradiation over the entire period (Skanse, 1948). In 

 the rat, large amounts of I 131 may result in cytological changes in the 

 anterior pituitary that are identical with those seen after thyroid removal 

 (Goldberg and Chaikoff, 1950). 



The thyroid apparently plays a negligible role in the total-body irradia- 

 tion syndrome. Radiation toxicity in the mammal is not altered appreci- 

 ably by thyroidectomy or thiouracil administration (Blount and Smith, 

 1949; Hempelmann et al, 1949; Haley et al, 1950). Toxicity may be 

 enhanced, however, when desiccated thyroid is given after irradiation 

 (W. W. Smith and Smith, 1951a). The potentiation of injury is prob- 

 ably related to elevated metabolism and is not specific for radiation 

 damage. 



An increase in uptake of I 131 by the thyroid has been noted after 

 irradiation of the whole body or the abdomen of rats (Evans et al, 1947). 

 The thyroid response occurs in the absence of the adrenals; it is not 

 observed in the newborn animal. While increased iodine uptake in the 

 adult animal is suggestive of an increase in thyroid function after irradia- 

 tion, the possibility exists that this may be related to anorexia and the 

 consequent decrease in dietary iodine. The fact that a definite increase in 

 the basal oxygen consumption of irradiated animals has not been demon- 

 strated argues against significant alteration of thyroid activity (Kirschner 

 et al, 1949; D. E. Smith, Tyree, Patt, and Jackson, 1951; W. W. Smith 

 and Smith, 1951b; Pratt et al, 1950; Patt, Swift, and Tyree, 1949). 



Pituitary. It is generally agreed that the pituitary is only slightly 

 sensitive to X rays. The early literature has been reviewed by Shields 

 Warren (1943b), who concludes that the normal gland is radioresistant, 



