Estrous cycle-dependent expression of estrogen receptor alpha in periodontal tissue

Estrogen receptor alpha (ERalpha) may play important roles in many estrogen physiological effects, but little is known about the fluctuation of ERalpha during the estrous cycle. In this study, the dynamic expression of ERalpha mRNA and protein in periodontal tissue during the estrous cycle were examined. Forty 12-week-old female rats were divided into four groups, based on the estrous cycle stage, and sacrificed. Immunohistochemistry and in situ hybridization were used to detect dynamic changes in ERalpha protein and mRNA in periodontal tissue during the estrous cycle, and data were analyzed by one-way ANOVA and cosinor analysis for temporal patterns. Significant differences (p<0.05) were found in the expression of ERalpha protein and mRNA among the four groups. The expression of ERalpha protein and mRNA exhibited an infradian rhythm with a period of about 120 h (five days). The phase and amplitude differences between ERalpha protein and mRNA were not significant (p>0.05). The results suggest the expression of ERalpha is dynamic during the estrous cycle and that in the future chronobiologic methods should be used to study the mechanism of estrogen effect on periodontal tissue.