Prostaglaridin E 2 adds bone to a cancellous bone site with a closed growth plate and low bone turnover in ovariectomized rats

Abstract

The objects of this study were to determine the responses of a cancellous bone site with a closed growth plate (the distal tibial metaphysis, DTM) to ovariectomy (OVX) and OVX plus a prostaglandin E 2 (PGE 2) treatment, and compare the site's response to previous findings reported for another site (the proximal tibial metaphysis, PTM). Thirty-five 3-month-old female Sprague-Dawley rats were divided into five groups: basal, sham-OVX, and OVX+0, +1, or +6 mg PGE 2/kg/d injected subcutaneously for 3 months and given double fluorescent labels before sacrifice. Cancellous bone histomorphometric analyses were performed on 20-μm-thick undecalcified DTM sections. Similar to the PTM, the DTM showed age-related decreases in bone formation and increases in bone resorption, but it differed in that at 3 months post-OVX, there was neither bone loss nor changes in formation endpoints. Giving 1 mg PGE 2/kg/d to OVX rats prevented most age-related changes and maintained the bone formation histomorphometry near basal levels. Treating OVX rats with 6 mg PGE 2/kg/d prevented age-related bone changes, added extra bone, and improved microanatomical structure by stimulating bone formation without altering bone resorption. Furthermore, after PGE 2 administration, the DTM, a cancellous bone site with a closed growth plate, increased bone formation more than did the cancellous bone in the PTM.