The effects of whole-body irradiation on the serum levels and kinetics of thyroid hormones in rats.

The effects of a single whole-body dose of X-rays on the serum levels and kinetics of thyroid hormones in rats were studied. The influence of radiation-induced anorexia was monitored by using pair fed control groups. A dose of 800 rad caused a reduction in T4 levels and 750 rad had a similar effect on T3; in each case the control group showed a smaller reduction. The kinetic results indicated that, in the control groups, the early reduction in hormone concentrations was caused, by a change in the distribution of the hormone; however, the continuing reduction in hormone levels in the irradiated rats appeared to results from decreased production. The results suggest that the thyroid system may play an active part in the early metabolic changes which follow whole-body irradiation.