EFFECTS OF PROSTAGLANDIN E(2) AND F2-ALPHA ON THE SKELETON OF OSTEOPENIC OVARIECTOMIZED RATS

This article contains the histomorphometric evaluation of the effects of prostaglandin F-2 alpha (PGF(2 alpha)) on cancellous bone from the lumbar vertebra and cortical bone from the tibial shaft of ovariectomi zed, osteopenic rats, These effects were then compared with those of p rostaglandin E(2) (PGE(2)). Three-month-old rats were either ovariecto mized (ovx) or shamovx. Then, either PGF(2 alpha) or PGE(2) in doses o f 1 and 3 mg/ kg/day was given subcutaneously for 21 days at 150 days post ovx, Histomorphometric analysis was performed separately on both the primary and secondary spongiosae of the fourth lumbar vertebral bo dies (LVB) and on tibial shafts, The ovx rats exhibited osteopenia in both primary (-23% to -37%) and secondary (-20%) spongiosae of the LVB , but not in the tibial shafts at 150 and 171 days post ovx, In the LV B, PGE(2) in doses of 1 or 3 mg/kg/day for 21 days restored trabecular bone volume to the levels of sham-ovx controls in the primary spongio sa, However, in the secondary spongiosa, the treatments only thickened the trabeculae. The effects of the PGF(2 alpha) treatment were simila r to those of the PGE(2) in both the primary and the secondary spongio sae. While both PGF(2 alpha) and PGE(2) treatments stimulated bone for mation in the LVB as indicated by the increases in labeled perimeter, tissue and bone area-based bone formation rates, PGE(2) is about 10 ti mes more potent than PGF(2 alpha) in these effects. The PGE, treatment also elevated activation frequency in the LVB, while the PGF(2 alpha) treatment did not, The treatments differed in that PGE(2) at these do se levels did not alter the eroded surface in the LVB while PGF(2 alph a) decreased it significantly, Thus, the increase of the ratio of labe led to eroded perimeter in the LVB in PGF(2 alpha)-treated animals was much more than that in PGE(2)-treated animals, In the tibial shafts, PGE(2) in doses of 1 and 3 mg/kg/day produced new marrow trabeculae in 2 of 6 and 3 of 6 of the ovx rats, However, no new trabecula was foun d in PGF(2 alpha)-treated tibial shafts, Higher doses of PGE(2) also i ncreased periosteal labeled perimeter, MAR, and BFR/BS, while PGF(2 al pha) did not produce any significant change in these parameters, Both PGE(2) and PGF(2 alpha) in doses of 1 and 3 mg/kg/day increased the la beled perimeter, MAR and BFR/BS and decreased the eroded pe rimeter in the endocortical surface, We concluded that both PGF(2 alpha) and PGE (2) in doses of 1 and 3 mg/kg/day for 21 days exhibited anabolic bone effects, The effects were mostly confined to an increase in trabecular volume in the primary spongiosa of the LVB and in the endocortical su rface of tibial shafts, The tissue level mechanism behind this appears to be that PGE(2) and PGF(2 alpha) can both stimulate osteoblast recr uitment and activity, Overall, we found PGE(2) to be more potent than PGF(2 alpha) at the same dose level at the endocortical surface, Furth ermore, new marrow trabecular bone formed only after PGE(2) treatment, PGF(2 alpha) differed from PGE(2) by significantly reducing the trabe cular eroded surface in ovx rats.