OBJECTIVETo elucidate the regulatory bio-mechanism of estrogen and local stress on the bone remodeling activities in vivo.

METHODSA Wistar rat experimental model was established to apply orthodontic activation during different stages of estrous cycle. In situ hybridization was used to detect the variation of the insulin-like growth factors (IGF) mRNA expression in the periodontal tissues. The data of each group was analyzed with SPSS 11.0 software package for Student-Newman-Keuls (S-N-K) test and one way ANOVA test.

RESULTSBoth IGF-I mRNA and IGF-II mRNA level expressed in the periodontal tissues were increased by orthodontic activation during various stages of the estrous cycle. But a similar pattern emerged that the IGF-I mRNA level was the lowest in the estrous stage, whereas its level was the highest in the proestrus stage (P < 0.05). No rhythm of IGF-II mRNA expression found during the estrous cycle.

CONCLUSIONIt was concluded that local mechanical stimulation directly enhanced the IGF expression. In contrast to the IGF-II, IGF-I was also influenced by the sex hormone rhythm during the estrous cycle.