Expression of estrogen receptor alpha and beta in the epiphyseal plate of the rat

In this study we examine the spatial and temporal expression of estrogen receptor (ER) alpha and beta 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 ER alpha and ER beta mRNA and protein in tibial growth plates from 1 to 40 weeks after birth. ER alpha and beta 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 ER alpha and beta in the resting cells. A similar expression pattern was observed during sexual maturation (7 weeks of age) except that ER beta mRNA was also detected in early proliferating chondrocytes. After sexual maturation (from 12 up to 40 weeks of age) ER alpha and beta mRNA and protein expression was confined to late proliferating and early hypertrophic chondrocytes. Apart from a relatively higher ER alpha mRNA expression in males after sexual maturation, we did not detect differences in expression of ERs between genders. Expression of ER beta 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 ER alpha and beta 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 ER alpha expression during sexual maturation per se.