ASSESSMENT OF SKELETAL AGING USING H-3-PROLINE TOPOGRAPHIC LABELING METHOD

Abstract

3H-proline was administered in multiple time-spaced doses and the animals were serially killed between 6 and 14 days later. Whole femora sectioned in longitudinal and 3 cross-sectional planes were prepared for autoradiography and subsequent grain count and micrometric analysis of the silver topographic bands which form over mineralizing surfaces. These bands, coincidental with the cellular uptake and turnover of radiotracer, allowed for the assessment of cellular rates of labeled matrical precursor production and deposition from which the processes of bone growth and remodeling and the effects of aging on the skeletal system can be evaluated. In addition, composite tracings of topographic data derived from multiple sections prepared at different geometric planes allowed for 3-dimensional mapping of skeletal events. The matrical rates of bone production in micrometers per day varied considerably from one surface to the next and decreased significantly with decreasing age. The rates of periosteal surfaces were twice those observed at the anterior periosteal surfaces of 5 wk old mice. By 26 wk the rates decreased to 1/8 times, respectively. Between 52-104 wk of age, no significant matrix production occurred at the periosteal surfaces. Endosteal activity was greater than twice the posterior periosteal rate at 5 wk, 1/4 times at 26 wk, and 1/8 times at 104 wk of age. Apparently, endosteal matrix production continued throughout life via active remodeling processes, but periosteal activity was turned-off by 52 wk. In old animals, subendosteal bone formation exhibiting hematopoietic activity is probably activated at 52 wk in focal areas. By 104 wk, subendosteal activity was distributed more extensively along the shaft. Continued metaphyseal remodeling resulted in removal of the residual epiphyseal plate structure and extension of the limits of the medullary canal.