The effects of age and sex on the expression of oestrogen and its receptors in rat mandibular condylar cartilages

Objective: Oestrogen expression may indicate a difference in resistance potential to mechanical strain. The purpose of this study was to investigate the expression of oestrogen and oestrogen receptors in mandibular condylar cartilages in male and female Sprague– Dawley rats at different ages. Materials and methods: One-hundred SD rats at the age of 2, 4, 8 weeks and 4, 12 months in both sexes, 10 in each age–sex group, were enrolled in this study. The expression of oestradiol, ERa and ERb was detected in mandibular condylar cartilages by the method of immunohistochemistry, and enzyme-linked immunosorbent assay or western blot. Results: Oestradiol and ERs immunoreactivity were obvious in mandibular condylar cartilages of SD rats. Oestradiol and ERa were observed in hypertrophic and mature layers, while ERb only in hypertrophic layer. There was no sex difference of same age (except 8-week age group) in the expression of oestradiol. The expression of both ERs, however, was usually higher in male than in age-matched female rats (P < 0.05), except that the 8-week-old female rats showed a higher ERa expression and the 4- and 8-week-old female rats showed a higher ERb expression than the age-matched male ones in western blot results (P < 0.05). Conclusions: The results that oestradiol, ERa and ERb are co-expressed in rat mandibular condylar cartilage, indicate that mandibular condylar cartilage is a target for oestrogen. The age and sex related differences in ERs expression may indicate a difference in potential to resist mechanical loading between genders at different ages.