Effects of total-body irradiation on growth, thyroid and pituitary gland in rhesus monkeys

Purpose: To investigate the effect of total-body irradiation (TBI) on growth, thyroid and pituitary gland in primates. Methods and materials: Thirty-seven rhesus monkeys (mean age 3.1 ± 0.6 years) received either a low-dose (4-6 Gy) TBI (n = 26) or high-dose (7-12 Gy) TBI (n = 11) and were sacrificed together with 8 age-matched controls after a post-irradiation interval of 5.9 ± 1.5 years. Anthropometric data were collected; thyroid and pituitary glands were examined; serum levels of thyroid stimulating hormone (TSH), free thyroxin (FT4), insulin-like growth factor-I (IGF-1) and its binding protein-3 (IGFBP-3) were measured. Results: Decrease in final height due to irradiation could not be demonstrated. There was a dose-dependent decrease in body weight, ponderal index, skinfold thickness and thyroid weight. The latter was not accompanied by elevation of TSH or decrease in FT4. Structural changes in the thyroid gland were found in 50% of the irradiated animals. Levels of IGF-I and IGFBP-3 did not differ between the dose groups, but the high-dose group had a lower IGF-1/IGFBP-3 ratio. Conclusion: Total body irradiation had a negative effect on body fat. There was no evidence of (compensated) hypothyroidism, but dose-dependent decrease in thyroid weight and changes in follicular structure suggest some effect of TBI on the thyroid gland. The decreased IGFI/IGFBP-3 ratio in the high-dose group can indicate that the somatotrophic axis was mildly affected by TBI. These results show that TBI can have an effect on the physical build and thyroid gland of primates even in the absence of cytostatic agents or immunosuppressive drugs.