Aging changes of estrogen and ER in rat TMJs

Objectives: To investigate the aging changes of estrogen and ER in rat TMJs. Methods: The expressions of estrogen and its two receptors were examined by immunohistochemistry in rat condylar cartilages from different ages. Then the expression were analyzed by the density of positive chondrocytes. Results:(1)Estradiol and ERa were abundant in hypertrophic and mature layers, especially in hypertrophic layer, while ERb was only expressed in hypertrophic layer. (2)When compared in different sexes of same age, the expression of estradiol showed no significant difference between male and female rats(p>0.05). But in some age groups, the expression of ERa and ERb in male rats was significantly higher than that of female rats with same age(p<0.05).(3)The expression of estrogen was highest in 4-week group(p<0.05), and then declined gradually and went relatively stable between 8 weeks and 16 weeks of age(p>0.05), with lowest level at 12-month and 18-month groups(p<0.05). While the expression of ER in male and female rats showed different trends. Conclusion: (1)Under physiological condition estrogen play an important role in cartilage proliferation and differentiation during puberty.(2)The expression of ER in condylar cartilage of normal male rats is higher than that of female rats with same age. In addition, the expression of ER in female rats declines gradually after puberty, while that in male ones remains higher level for longer time, which may be related to the predilection of TMD in women.