Fatty Marrow and Increased Loaded Cancellous Bone was Resistant to OVX induced Bone Changes in Female Rats

Abstract

ObjectivePrevious studies determined ovariectomy (OVX) induced cancellous bone loss and raised cage (RC) bipedal stance partially prevented OVX induced bone loss at red marrow bone sites in adult rats; however, these effects in the distal tibial metaphysis (DTM) with fatty marrow, a site similar to adult long bone metaphyses (non‐veterbral bone sites) with low risk of postmenopausal fracture, have yet to be determined.MethodsSix‐month‐old female S‐D rats were divided into basal, sham, OVX, RC and combination of OVX plus RC exercise for 4 and 8 weeks, cancellous bone histomorphometry on fluorescent labeled undecalcified cross sections of DTM were performed.ResultsIn DTM, OVX did not induce cancellous bone loss, but significantly increased bone turnover. RC exercise alone had no effect on cancellous bone mass, but significantly reduced bone resorption. Unlike in high turnover red marrow sites, the combination of RC exercise and OVX only partially prevented bone loss, but combining with raised cage exercise and OVX in DTM totally inhibited OVX induced cancellous bone loss by depressing bone resorption (reduced eroded perimeter).ConclusionsIn DTM, the inhibition of OVX induced bone loss can be attributing to a combination of fatty marrow content and increased mechanical loading with decreased resorption, which may partly explain why non‐vertebral bone sites are less at risk to fracture in postmenopausal patients.