Changes in the Osteoblastic and Mitochondrial Population of Aging Periosteum

Abstract

EARLY investigators^1–4 interested in the physiology of bone have described filamentous, rod- and granular-shaped mitochondria in osteoblasts from a variety of animals both in vivo and in vitro. An apparent relation between the number of mitochondria and osteoblastic activity was also pointed out. Pritchard⁵ arrived at the same conclusion. Within the past decade numerous biochemists have revealed a good many of the substrates and enzymes involved with intermediary metabolism associated with mitochondria. More recently, cytochrome oxidase and succinic dehydrogenase activity of the periosteum was studied in normal and traumatized rat femora from birth to old age^6,7. The results showed high levels of activity of respiration becoming more elevated at the period of maximum rate of bone formation. Following this period of intense activity (5 weeks of age), a sharp drop occurred to a low level, which was maintained throughout the life of the animal. Trauma to the femora stimulated a response of respiratory activity, however, the response becoming progressively less with increasing age. Changes in respiratory enzyme-levels are fundamental to the activity of cells in general, because these enzymes are part of the aerobic hydrogen transport system from which rich-energy-bond phosphate is generated.