Trabecular bone response to mechanical loading in ovariectomized Sprague-Dawley rats depends on baseline bone quantity

Abstract

Mechanical loading is one of the determining factors for bone modulation, and is therefore frequently used to treat or prevent bone loss; however, there appears to be no data on the effects of baseline bone quantity on this response. This study aimed to verify whether baseline bone quantity affects osteoporotic trabecular bone adaptive response to mechanical stimulation.

Twenty-four female Sprague-Dawley (SD) rats were ovariectomized (OVX). After 3 weeks of OVX, rats were divided into a high bone quantity and a low bone quantity group, and rats in each group were then subdivided into 4 groups that were exposed to different loading strategies. In the loading groups, tibiae were stimulated through axial loading at 2000 με of strain, for 1500 cycles each of 75 s, 150 s, or 250 s. The sham treatment groups received no loading.

Changes in BV/TV for trabecular bone in the tibia were measured at the baseline (before loading), and at 3 weeks and 6 weeks after loading. BV/TVs in loading groups of the low baseline bone quantity group were significantly increased at 6 weeks, compared with those in the no-loading groups (p<0.05), while those in the high quantity groups were not increased (p>0.05). A significant negative correlation was observed between baseline BV/TV and its relative variations at 3 weeks or 6 weeks (p<0.05).

These results indicate that adaptive responses of osteoporotic trabecular bone to mechanical loading depend on baseline bone quantity.

Introduction

Mechanical loading is an important factor for regulating bone adaptation (Frost, 2004, Ko et al., 2011, Qin et al., 1998, Turner, 1998). Based on these factors, previous studies have attempted to verify the feasibility of mechanical loading for the treatment osteoporosis. However, the reported effects of mechanical loading on osteoporosis have been varied widely (Lynch et al., 2010, Lynch et al., 2011, Prisby et al., 2008, Totosy de Zepetnek et al., 2009, Turner et al., 2011, van der Jagt et al., 2012). The reason for diverse effects of mechanical loading is unclear, but differences in baseline bone quantity may be responsible.

Previous studies suggested that bone adaptive responses to mechanical loading depend on its parameters (Jarvinen et al., 2003, Judex et al., 2007, Turner et al., 1995) as well as age and genetics (De Souza et al., 2005, Robling and Turner, 2002, Robling et al., 2007) of subjects applied by loading. However, to our knowledge, few studies have reported the effects of baseline bone quantity on the response of bone to mechanical loading in rats of an identical animal strain.

This study aimed to verify whether baseline trabecular bone quantity affected the response of trabecular bone to mechanical loading on osteoporotic bone.