Effect of X-irradiation on growth and the expression of parathyroid hormone-related peptide and Indian hedgehog in the tibial growth plate of the rat

Aim: To study the effect of irradiation on the longitudinal growth and the expression of parathyroid hormone-related peptide (PTHrP) and Indian hedgehog (IHh) in tibial growth plates of rats. Methods: At 3 weeks of age, 30 male rats received a single fraction of irradiation (8 Gy) to their right hind limb, and small groups of animals were sacrificed 1, 2, 3, 5, 7, 10, 15, and 26 weeks after irradiation. Weight and length of both irradiated and nonirradiated tibiae were measured, and sections of the tibiae were stained with HE. PTHrP and IHh were visualized using immunohistochemical techniques. Results: Radiation resulted in persistent growth delay of the irradiated tibiae, with a difference in length of more than 10% between the irradiated and the nonirradiated tibiae 15 weeks or more after irradiation. The growth plate architecture was disturbed, and the expression of both PTHrP and IHh was decreased in the irradiated tibiae. Conclusion: As PTHrP and IHh are key regulators of both the pace and the synchronization of the differentiation of growth plate chondrocytes, the reduced expression of PTHrP and IHh may contribute to the changes found after irradiation.