ESTROGEN-RECEPTOR MESSENGER-RNA IS EXPRESSED IN-VIVO IN RAT CALVARIALPERIOSTEUM

Estrogen deficiency is well recognized as a cause of bone loss in rats and humans. Likewise, treatment with estrogen results in prevention o f this loss. Initially, this effect was thought to be indirectly media ted but, more recently, estrogen receptors (ER) have been reported in osteosarcoma cells and primary cultures originating from surgical wast e, suggesting a direct effect of this steroid hormone. Detection of ER in skeletal tissues, however, has remained elusive. The purpose of th is investigation was to establish the efficacy of the highly sensitive reverse-transcription polymerase chain reaction (RT-PCR) technique to detect ER in a well defined skeletal tissue (calvarial periosteum) th at is responsive to the hormone. Primers were made specific to rat ER sequences. Total RNA was extracted from rat uterus, liver, spleen, and the periosteum using an organic solvent method. cDNA was synthesized from 2 mu g total RNA. cDNA corresponding to 40 ng total RNA/sample pr oduced intense PCR products for ER. In descending order of intensity w ere uterus, liver, bone, and spleen. Importantly, a similar time-cours e for estrogen-induced down-regulation of steady-state mRNA levels for alkaline phosphatase and osteonectin was observed in calvarial perios teum and tissues known to express estrogen receptors. These data provi de in vivo evidence of ER mRNA in bone and suggest that at least some of estrogen's action on bone is directly modulated.