Cranial irradiation of female rats causes dose-dependent and age-dependent activation or inhibition of pubertal development.

Cranial irradiation in prepubertal children with leukemia or brain tumors can lead to precocious or in high doses to late puberty. To unravel the underlying mechanisms, we developed a rat model with selective cranial Co60-irradiation technique. Infantile (12-16 d old) or juvenile (21-23 d old) female Sprague-Dawley rats received a single dose of 4, 5, 6, 9 or 2 x 9 Gy (at days 21 and 23). Each group consisted of 7-20 animals. High radiation doses (9 Gy and more) caused retardation of sexual development, whereas low radiation doses (5 or 6 Gy) led to accelerated onset of puberty in 20% of infantile irradiated rats animals as determined by vaginal opening. Interestingly, at peripubertal age (postnatal day 32-34), 5 or 6 Gy infantile irradiated rats had significantly higher serum LH levels stimulated by GnRH and estradiol levels (p < 0.05). 2 x 9 Gy irradiated rats had at the age of 3 mo a marked growth retardation and significantly lower GH levels than the controls (p < 0.05) whereas prolactin, FSH, TSH, T4, and corticosterone levels were comparable with controls. These studies demonstrate that the GnRH-pulse generator is very radiosensitive as precocious activation occurred after low dose irradiation (5 or 6 Gy) of infantile rats without any other endocrine disorder. High radiation doses (9 or 2 x 9 Gy) induced retardation of sexual maturation and later on growth hormone deficiency. Moreover this model of cranial irradiation seems to be suitable to study the molecular mechanisms of radiation induced pubertal changes.