Bone Abstracts

Lactation in both humans and mice is associated with a substantial bone loss, in mice this bone loss is recovered within 4 weeks after weaning. This recovery is considered to be the most rapid physiological bone formation in adult life. The aim of the study was to investigate the effect of the post-lactational anabolic response on a disuse bone loss induced by Botulinum toxin (BTX).

Forty-eight NMRI mice were divided into the following groups: pregnant, lactation, recovery+saline, recovery+BTX, and a virgin control group. The lactation period was 12 days with a subsequent recovery period of 21 days. On day 1 of recovery, 2 IU of BTX/100 g body weight was injected into the right hind limb. The experiment was approved by the Danish Animal Experiments Inspectorate.

The lactation resulted in a substantial loss of bone strength (femoral neck: –63%, P<0.001 and femoral mid-diaphysis: –37%, P<0.001 vs pregnant) as well as a substantial loss of bone density (BV/TV: –47%, P<0.001, vBMD: –45%, P<0.001, Tb.Th: –24% P<0.001 vs pregnant). In the saline injected animals a close to complete recovery was observed, at the end of the recovery period. In the BTX injected recovery animals no additional decrease in bone strength or Tb.Th was observed compared to lactation. However, a decrease in bone density was observed (BV/TV: –49%, P<0.001, vBMD: –53%, P<0.001, vs lactation), but, interestingly, bone formation was increased (BFR/BS: 46% P=0.002 vs virgin control).

The post-lactational anabolic response prevented an immobilization induced loss of bone strength and Tb.Th, but did not mitigate the loss of BV/TV and vBMD, although an increased bone formation rate was found in BTX injected recovery animals.