Effect of Aging and X-Irradiation on the Kinetics of Skeletal Metabolism in the Rat

Abstract

The instantaneous rate of skeletal growth and metabolism in normal aging and after cxposure to x-irradiation is compared. The radioisotope technique of Bauer was employed to quantify the alterations in the rate of accretion (A) and calcium exchange capacity (E) of various bones of young growing rats after whole- and partial-body x irradiation. In the animals in which one limb was exposed to 2000 r of x irradiation and compared with its contralateral control, the accretion rates of both the ends and the shaft of the tibia of the irradiated limb were depressed considerably, but the exchange capacity of the ends of the irradiated tibia showed a marked increase. In the tibiae exposed to 800 r, no effect on the accretion or exchange values was observed. It was found that, the A and E per unit ash weight differ markedly among the various bones and in different fractions of individual bones, and they were also differentially affected by radiation. Both these parameters in all bones, except the incisors, decreased as a function of age over the 140-day study period. After 500 r of whole-body x irradiation, the accretion rate decreased, whereas the exchange capacity of most bones showed a slightmore » increase over that of the controls. These changes were most marked at 75 days after irradiation and showed a tendency toward recovery at 140 days. The whole-body x irradiation (500 r) must have an abscopal effect on skeletal growth, since 800 r delivered directly to the bone hnd no acute effect on either the A or the E value. Whether the effect of 500 r of wholebody irradiation is due to the resulting temporary inanition with its inhibition of body growth, or to a generalized effect on the body's calcium regulatory control mechanism, is not clear. Although the gross effects on skeletal tissue of aging and radiation are similar, closer observation of these processes (by measurement of metabolic parameters) indicates that they differ in certain respects. Thus, in terms of exchange capacity, there is no simple relationship between the effects of x irradiation and those of aging on skeletal metabolism. (auth)« less