17-BETA-ESTRADIOL SUPPRESSES GENE-EXPRESSION OF TARTRATE-RESISTANT ACID-PHOSPHATASE AND CARBONIC-ANHYDRASE-II IN OVARIECTOMIZED RATS

Tartrate-resistant acid phosphatase (TRACP) and carbonic anhydrase II (CA II) are key enzymes responsible for osteoclastic bone resorption. In this study, we proposed that estrogen loss in postmenopausal osteop orosis may enhance gene expression of TRACP and CA II, and subsequentl y increase osteoclastic bone resorption. We have, therefore, used the ovariectomized rat model of postmenopausal bone loss to investigate ch anges at the gene transcriptional level in osteoclastic bone-resorbing enzymes in ovariectomized (OVX) rats, sham ovariectomized (S-OVX) rat s, and estrogen-treated ovariectomized (E-OVX) rats. We have demonstra ted for the first time that ovariectomy in rats enhances gene expressi on of TRACP and CA II. The mRNA levels in OVX were approximately three - and four-fold higher, respectively, than those in S-OVX. Enhancement was observed 1 week after ovariectomy and transcripts remain high dur ing the experimental period of 8 weeks. Administration of 17 beta-estr adiol to OVX (E-OVX) reduced gene expression of these osteoclastic bon e-resorbing enzymes 18 hours after injection. It appeared that the sup pression of the osteoclastic bone-resorbing enzymes by 17 beta-estradi ol was most effective during the first 1-2 weeks but the degree of sup pression was reduced at 8 weeks after ovariectomy. In conclusion, our results suggest that estrogen prevents bone loss by reducing the mRNA levels of osteoclastic bone-resorbing enzymes in bone tissue.