The role of osteocytes in bone resorption during lactation: morphometric observations.

It has been suggested that osteocytes may resorb bone during the calcium mobilization that occurs during lactation. To test this hypothesis morphometric methods were used to evaluate changes in mature nonmated female rats, 6-day postpartum nonlactating rats, 21-day postpartum nonlactating rats, 6-day lactating rats, 15-day lactating rats, and 21-day lactating rats using femur cross sections in the diaphyseal region. Osteoclast resorption per unit length of periosteal surface, as well as other measures of resorption activity, demonstrated that by 15 days of lactation a significant mobilization of calcium was occurring. The volume density of osteocyte lacunae and individual lacunar volumes from serial section reconstruction showed no increase in the lactating groups. Indeed, the only significant change in lacunae volume was a decrease apparently due to pregnancy. It is concluded from this study that osteocytes do not resorb bone during lactation.