Comparison of the protective effects of melatonin and amifostine on radiation-induced epiphyseal injury.

PURPOSE

We compared the effects of amifostine and melatonin in preventing radiation-induced epiphyseal growth plate injury in rats.

MATERIALS AND METHODS

Four-week-old (65-85 g), growing male Sprague-Dawley rats were randomly assigned to receive radiation alone, at 25 Gy in three fractions (group R), or this dose of fractionated radiation proceeded by prophylactic amifostine 200 mg/kg i.p. (group A), melatonin 15 mg/kg i.p. (group M), or amifostine + melatonin (group AM). The right rear extremity of each animal was irradiated while the contralateral leg was shielded from radiation, as a control. Bone growth based on the length of the tibia, femur, and overall limb was calculated 6 weeks after the treatment.

RESULTS

In groups R, A, M, and AM, the mean growth loss (GL) for the overall limb was 56.9 +/- 8.1%, 46.8 +/- 7.7%, 36.6 +/- 4.3%, and 38.5 +/- 5.1%, respectively. The limb length discrepancies (LLD) in groups R, A, M, and AM were 13.8 +/- 1.4%, 10.5 +/- 0.3%, 7.4 +/- 0.7%, and 8.8 +/- 1.1%, respectively. Differences in LLD were significant between each treatment group and group R (range: p = 0.0001-0.001). Differences in either of mean GL and LLD were not significant between groups M and AM; however both of these groups had significantly less GL and LLD than group A.

CONCLUSIONS

We observed a superior radioprotective function of melatonin over amifostine in preventing radiation-induced epiphyseal growth plate injury, without any increase in radioprotective effect by adding amifostine to melatonin.