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Spontaneous and Radiation-Induced Benign Tumors in Parabiont Rats

S. Warren, O. Gates, C. E. Brown, R. N. Chute and M. W. Porter
Radiation Research
Vol. 75, No. 1 (Jul., 1978), pp. 98-107
DOI: 10.2307/3574872
Stable URL: http://www.jstor.org/stable/3574872
Page Count: 10
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Spontaneous and Radiation-Induced Benign Tumors in Parabiont Rats
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Abstract

Spontaneous benign tumors are present in nearly half of NEDH rats. A single whole-body exposure of 1000 R X radiation delivered to a rat supported by a shielded parabiont partner induced high incidence rates of benign tumors in several radio-responsive organs: ovary, 49.7%; adrenal medulla (males, 23.9%; females, 15.2%); mammary tissue (females, 19.6%); islands of Langerhans (males, 15.3%); and liver (cholangiomas) (males, 7.4%; females, 13.8%). Both hormonal imbalance and radiation effects appear to be involved. Parabiosis decreased the incidence of pheochromocytoma, but irradiation of a partner increased it. Mammary tumors occurred on the average 200 days earlier in irradiated rats than in their unirradiated controls. Benign tumors rarely affected health. The incidence was not increased in most organs following irradiation. Three control series were used: single rats, control parabiont rats and the shielded partners of the irradiated partners. Although endometrial polyps were more frequent in irradiated than in shielded partners, they probably resulted from hormonal imbalance. Adenomas of the pituitary were most frequent in shielded female parabiont partners (16.0%). Their incidence was decreased by radiation to 4.2%. Most types of benign tumors rarely progress to malignancy.

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