Age-dependent morphometric change in the lumbar vertebrae of male and female rats: comparison with the femur.

The morphological parameters, bone area, marrow area, bone-to-bone+marrow ratio, periosteal-to-total bone surface ratio, and surface-to-volume ratio, were studied in the fourth and fifth lumbar vertebrae of male and female rats (Heiligenberg strain) between birth and the end of lifespan. With increasing age, the bone area and marrow area increased for all ages, whereas the bone-to-bone + marrow ratio, periosteal-to-total bone surface ratio, and surface-to volume ratio decreased during the first 150 days. Afterwards, the bone-to-bone + marrow ratio decreased, whereas the periosteal-to-total bone surface ratio and surface-to-volume ratio were nearly constant. Modelling data were measured by use of the vital labeling technique with calcein. From the stained bone area the bone formation and the bone resorption rates were calculated. The bone formation rate, about 8300%/year, was highest after birth and decreases continuously with increasing age to 14%/year. The bone resorption rate, about 1100%/year, was highest after birth and decreased continuously with increasing age to 9%/year, whereas for all ages the bone formation rate was higher than the bone resorption rate, which led to an increase in bone area. The values obtained for the lumbar vertebra are compared with literature data and with the corresponding data for the distal femur obtained under identical conditions.