LONG TERM EFFECTS OF DEUTERON IRRADIATION OF THE RAT PITUITARY1

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Abstract
An investigation has been made of the long-term effect of low radiationr doses to the rat pituitary using a high energy deuteron beam. The pituitarics were irradiated when the rats were 28 days old. The animals were maintained up to 27 months thereafter. A total of 138 controls and 169 treated rats were studied. Groups varying in size from 7 to 20 rats at each dose of radiation were sacrified at intervals of about 3 months. The endocrine changes became increasingly more prominent with increasing dosage and with time. Within certain dose ranges the same terminal results were obtained, though the lower the close the longer theperiod which elapsed before the maximum effect resulted. The effect of the radiation on pituitary structure was as follows:decrease in size of all lobes; loss of demarcation between lobes; increased connective tissue in surrounding membranes and supporting framework and frequent small hemorrhages. In the anterior lobe the change effected in the shortest time and at the lowest dose was degranulation and disappearance of acidophils. Basophils were less severed damaged. This differential action of radiation on the two types of chromophils was not noted in the earlier series of experiments reported, where higher deuteron dosage was applied to the pituitary and prompt injurious action on its parenchyma resulted. The endocrine changes in organs dependent on pituitary secretion appeared in the following sequence: reduction in adrenal weight with adrenal cortical atrophy; decrease in thyroid size and evidences of inactivity; testicular atrophy, regression of male accessory organs and failure of sperm production. The sensitivity of body growth impairment was difficult to evaluate relative to other endocrine alterations, at least at lower doses of radiation, after which the endocrine changes did not supervene at once; body size, particularly length, could not regress, whereas the weight of the endocrine organs could. The severity of all these changes following irradiation, judged by weight or histological structure or function, increased with dosage as did the speed of onset. Adenomata were observed in pituitaries which had been irradiated with low doses. At the lowest doses, tumor incidence in irradiated pituitaries was three fold greater than in pituitaries of controls of the same age, whereas, at high doses tumor formation was suppressed. The tumors were derived from chromophobes, chiefly, but from acidophils and basophils as well; mixed-cell adenomata were also observed.