Expression of estrogen receptor α and β in the epiphyseal plate of the rat

In this study we examine the spatial and temporal expression of estrogen receptor (ER) α and β mRNA and protein in the tibial growth plate of the rat after birth, as well as the hormonal regulation of their expression. Using in situ hybridization and immunohistochemistry, we demonstrated ERα and ERβ mRNA and protein in tibial growth plates from 1 to 40 weeks after birth. ERα and β mRNA and protein were localized in late proliferating and early hypertrophic chondrocytes during early life (1 and 4 weeks of age), whereas the immunohistochemistry also showed staining for ERα and β in the resting cells. A similar expression pattern was observed during sexual maturation (7 weeks of age) except that ERβ mRNA was also detected in early proliferating chondrocytes. After sexual maturation (from 12 up to 40 weeks of age) ERα and β mRNA and protein expression was confined to late proliferating and early hypertrophic chondrocytes. Apart from a relatively higher ERα mRNA expression in males after sexual maturation, we did not detect differences in expression of ERs between genders. Expression of ERβ mRNA in epiphyseal plates was increased in growth-retarded hypophysectomized rats compared with controls. Administration of growth hormone (GH) did not reverse the increased ER expression to normal. These data suggest that ERα and β are coexpressed in growth plates of the rat after birth and that the level of expression of ERs in these tissues is hormonally regulated. Furthermore, our data indicate that the absence of growth-plate closure in the rat cannot be explained by disappearance of ERα expression during sexual maturation per se.