A scanning electron microscopic and photon absorptiometric study of the development, prolongation, and pattern of...

Measurements by scanning electron microscopy (SEM) of femoral hemisections confirmed and amplified results by single-photon absorptiometry that had shown a marked increase in lactation osteopenia in rats fed a low-calcium diet (LCD, 0.04% Ca) as compared with a medium-(adequate) calcium diet (ACD, 0.4% Ca). SEM of bones from rats at the end of lactation on either diet showed a large loss of trabecular bone, increased porosity of endosteal surfaces, and cortical thinning. These changes were much more striking in LCD rats than in ACD rats. Backscattered electron imaging of cross sections of the femora revealed marked cortical thinning at midshaft after lactation, especially in rats on the LCD; this method also showed a marked increase in newly formed, less dense diaphyseal bone on the endosteal surface when dietary calcium had been made available to the LCD rats after lactation ceased. Unlike the rats fed the ACD after lactation, the rats continued on the LCD for the first 3 weeks postlactation failed to recover bone mineral, even though there was a marked decrease in resorbing surfaces of the femora as revealed by morphologic examination. When the diet was changed from the LCD to the ACD for the second 3 weeks postlactation (week 4-6), the bone mineral increased substantially. Overall, these results demonstrate the marked loss of bone during lactation, especially severe in rats fed a low-calcium diet, and the rapid postlactational recovery of bone when adequate dietary calcium was made available, even if the recovery had been delayed for the first 3 weeks by feeding a diet very low in calcium.