Effect of pregnancy, lactation and weaning on bone mineral density in rats as determined by dual-energy X-ray absorptiometry.

To elucidate the effect of pregnancy, lactation and weaning on bone mineral density (BMD) in rats, a longitudinal study was done on the same individuals measuring BMD by dual-energy X-ray absorptiometry (DXA) and comparing their profiles with those of nonpregnant controls. Twenty-seven pregnant Wistar rats which had been mated at 11 weeks old (baseline), lactated during the three weeks postpartum period and weaned thereafter. Twenty-four rats of the same age served as nonpregnant controls. BMDs in lumbar spine, distal femur and caudal spine of all rats were measured weekly from 11 to 22 weeks except for the week of parturition (14th week). During pregnancy, BMDs of the three sites increased significantly from the baseline values, but no significant difference was observed in comparison with the control. After parturition and during lactation, BMD of the three sites decreased significantly from the pregnant values and decreased even from baseline values. All the BMD values of the pregnant group were significantly lower than those of the control group. After weaning, BMDs of the three sites increased gradually and caught up to the control group at 22 weeks in the lumbar spine and the femur and at 21 weeks in the caudal spine. In conclusion, pregnancy in itself does not significantly affect maternal BMDs of rats, although the significant bone mineral loss during lactation is not completely restored until at least 5 weeks after weaning.