INTERMITTENT ON OFF PROSTAGLANDIN E-2 AND RISEDRONATE ARE EQUALLY ANABOLIC AS DAILY PGE(2) ALONE TREATMENT IN CORTICAL BONE OF OVARIECTOMIZED RATS/

In this study, we evaluated the rat cortical bone changes after a two- cycle, 60-day each (ON/OFF/ON/OFF) treatment with either prostaglandin E-2 (OVX/c-PGE(2)) alone or in combination with risedronate (OVX/c-PG E(2)+Ris), in comparison with daily treatment with PGE(2) for 240 days (OVX/PGE(2)-240d) in ovariectomized (OVX) rats, At the end of the stu dy, we found that: (1) the overall effectiveness of the treatment on b one mass hi the tibial shaft indicates the following ranking: OVX/PGE( 2)-240d = OVX/c-PGE(2)+Ris > OVX/c-PGE(2) > OVX/c-Ris greater than or equal to OVX = aging; (2) the same bone mass and architecture were pro duced in the OVX/PGE(2)-240d and the OVX/c-PGE(2)+Ris groups, but the histomorphometric profiles differed in that the former exhibited a hig her bone turnover and index of resorption; (3) OVX/c-PGE(2)+Ris treatm ent prevented endocortical bone loss and minimized trabecular bone los s during the OFF periods; and (4) the OVX/c-PGE(2) alone treatment res ulted in the accumulation of less total bone than OVX/PGE(2)-240d and OVX/c-PGE(2)+Ris because it could not maintain most of the new subendo cortical and marrow trabecular bone generated earlier, in summary, bot h continuous daily PGE(2) and two cycles ON/OFF combined PGE(2) and Ri s treatments result in more Bone mass than two cycles ON/OFF PGE(2) al one and Ris alone in estrogen-deficient rats, This study showed that t he anabolic effects of PGE(2) can be induced and maintained either-by continuous administration or by cyclical PGE(2)+Ris.