Anabolic effect of prostaglandin E-2 on cortical bone of aged male rats comes mainly from modeling-dependent bone gain

In this study, prostaglandin E-2 (3 mg/kg per day) was administered to 20-m onth-old male Wistar rats for 10 and 30 days. Histomorphometric analyses we re performed on double-fluorescent-labeled undecalcified tibial shaft secti ons. Thirty days of prostaglandin E-2 (PGE(2)) administration increased bon e formation rate/total bone surface from undetectable levels to 0.6 mu m/da y at the periosteal surface and from 0.5 to 2.1 mu m/day at the endocortica l surface. Endocortical osteoid surface area increased from 2% to 67% at da y 10 and decreased to 6% at day 30; woven and lamellar bone formation start ed at day 0, but was most obvious at day 30, resulting in a 12% increase of total bone mass. The red to yellow marrow ratio was 0.2 in pretreatment co ntrols, and increased to 1.6 by day 10 and 2.4 by day 30 with PGE(2) admini stration. Intracortical cavity number and area increased after 10 days of P GE(2) treatment, but with forming osteon number and area far exceeding thos e of resorption cavities at day 30, Endocortical modeling surface/endocorti cal surface was only 1.5%, and remodeling was 11.1% in pretreatment control s. PGE(2) treatment increased modeling to 24.5% in the 10 day group and 93. 7% in the 30 day group, whereas remodeling remained unchanged at 10 days, a nd decreased to 6.2% at 30 days. Osteoprogenitor cells and osteoblasts coul d not be detected in pretreatment controls, but increased by day 10, and re turned almost to control levels by 30 days. Our data indicate that PGE(2) i nduced periosteal and endocortical bone formation mainly by modeling-depend ent bone gain, accompanied by increases in intracortical remodeling and red bone marrow, and a transient increase in the osteoprogenitor cells adjacen t to the endocortical surface, These findings suggest that 20-month-old mal e Wistar rats were very responsive to the anabolic action of PGE(2) in the tibial shaft, a site consisting mainly of cortical bone and yellow marrow. (C) 1999 by Elsevier Science Inc. All rights reserved.