Bone status of senescent female rats: Chemical, morphometric, and biomechanical analyses

Abstract

The bone status of female rats, 6, 12, and 24 months of age was examined. Femur Ca, Pi, and osteocalcin contents, as well as biomechanical properties, were measured and correlated to physical indices and serum chemistry. Diaphyseal Ca, Pi, and osteocalcin did not change significantly with increasing age. Serum Ca and Pi concentrations were not altered in the aged rat. Immunoreactive parathyroid hormone (PTH) levels increased significantly with age, when analyzed by linear regression. Serum osteocalcin decreased progressively from 6 to 12 months (-21%) and from 12 to 24 months (-23%). Maximum breaking force required to fracture femurs at midshaft did not change with senescence. Hence, the strength of the femurs as an intact organ was not compromised in aging. However, ultimate stress, a parameter that normalizes for differences in bone geometry and size, decreased 14% from 12 to 24 months. Changes in other biomechanical parameters, including yield and ultimate deformation, strain, and modulus of elasticity, were relatively small, but statistically significant, or were negligible. Morphometric measurements indicated a progressive age-related increase in second moment of area and cortical area. Medullary area did not change with age. Therefore, strength of the intact femur was maintained by architectural compensations, although normalized tissue strength decreased in senescence. The bone status and Ca/Pi homeostasis of the female rat were compared to similar findings, reported previously, for the male animal. The results suggest that bone status and mineral metabolism were compromised in the aged female rat, but the magnitude of change was less than that found for the senescent male rat.

Are skeletally mature female rats a suitable model to study osteoporosis?

“…Kiebzak and cols. (20) did not show agerelated increases in PTH levels of female rats at 24, 48 and 96 weeks of age; however, immunoreactive PTH titers were slightly, but significantly, elevated when the data were analyzed by linear regression. In humans, Sa raiva and cols.…”

“…Kiebzak and cols. (20) did not show agerelated reductions on serum calcium concentration in female rats with 24, 48 and 96 weeks of age, either, using ani mals that were also fed a diet adequate in calcium. In addition, Takada and cols.…”

“…Kiebzak and cols. (20) showed that serum OC decreased progressively from 24 to 48 weeks of age (21%) and from 48 to 96 weeks of age (23%) in female rats; however, these investigators did not show total se rum alkaline phosphatase activity alteration with aging in the same female rats. Iida and Fukuda (28) showed decreased in the total ALP activity up to 36 weeks of age in Wistar female and male rats.…”

Nonproliferative and Proliferative Lesions of the Rat and Mouse Skeletal Tissues (Bones, Joints, and Teeth)

“…Angevine and Clemmons (1957), Benke et al (1972), Ellis and Peart (1971), Kiebzak et al (1988a), Kiebzak et al (1988b), Leininger and Riley (1990), Long et al (1996), Thompson (1973)…”

Classical Models of Senile Osteoporosis

“…[30][31][32][33][34][35] Like C57BL/6 mice, the rat strain F344 has often been used for aging research, although Sprague-Dawley and Wistar rats have also been analyzed. Trabecular bone volume of the vertebra of rats reportedly does not exhibit a decrease at 12 months of age, in contrast to mice 31,32,34,35 ; however, although the time course and structural changes in bone aging phenotypes differ between these rodents, both experience age-related bone loss. As a system, mice are advantageous because of the availability of genetic manipulation techniques, but because of their larger size rats represent a more appropriate system to study alterations in the vascular system.…”