Lumbar vertebral cancellous bone is capable of responding to PGE(2) treatment by stimulating both modeling and remodeling-dependent bone gain in agedmale rats

Previously we found that PGE(2) 3 mg/kg in 20-month-old male rats induced m assive bone formation mainly by modeling dependent bone gain in cortical bo ne. It is not known whether cancellous bone will respond similarly; thus, w e evaluated the effect of PGE(2) on cancellous bone of the same aged rats. Thirty-four 20-month-old Wistar male rats were given PGE(2) (3 mg/kg/day) o r vehicle subcutanously for 10 and 30 days. Double fluorescent labels were injected 9 and 2 days prior to the sacrifice. Histomorphometry was performe d on 1% toluidine blue stained and unstained sagittal sections of lumbar ve rtebral bodies. The results demonstrated that 10-day PGE(2) treatment incre ased osteoprogenitor cells, osteoblasts (x2-fold), osteoid (x4.5-fold), wov en bone formation (0.04%), and 40% more trabecular area; it stimulated mode ling (x2-fold) and remodeling-dependent (x1.5-fold) bone formation with inc rease of mineralization lag time (MLT, x 7.5-fold). Thirty-day treatment su stained increases in osteoblast numbers, modeling, and remodeling-dependent bone formation and further stimulated woven bone formation (6.6%), turnove r (x3-fold), and trabecular area and number (x2-fold). Osteoprogenitor cell s were undetectable along with 70% less osteoid area compared with 10-day t reatment but still was 1.5-fold higher than aging controls. MLT returned to aging control level. It was concluded that the aged cancellous bone of 20- month-old male Wistar rat retains a capability of responding to the anaboli c effect of PGE(2). Osteoblastogenesis and enhanced modeling and remodeling -dependent woven or lamellar formation contribute to this anabolic action. Bone formation differed in that the endocortical surface of cortical bone w as stimulated mainly by modeling whereas both modeling and remodeling-depen dent bone gain were equally stimulated at the trabecular surface of the lum bar vertebral body.