Increased3H-uridine levels in osteocytes following a single short period of dynamic bone loadingin vivo

Abstract

Both ulnas of skeletally mature roosters (Gallus domesticus) were deprived of functional load bearing by proximal and distal submetaphyseal osteotomies. Twenty-four hours later the animals were injected with 1.5 mCi of 3H-uridine and the ulna on one side was subjected to a single period of a cyclical load engendering physiological strain levels at 1 Hz for 6 min. Twenty-four hours after loading the animals were killed. Autoradiographic examination of comparable regions of cortex in sections from the bone's midshafts showed that in the loaded bones, 72 +/- 2.7% of osteocytes were labeled compared with 12 +/- 3.5% in the corresponding areas of their contralateral nonloaded pair (P less than 0.001). The number of grains per labeled osteocyte was also higher in the loaded side (6 +/- 0.5 compared with 4 +/- 0.5, P less than 0.01). There was no obvious correlation between the longitudinal strain distribution during artificial loading and the distribution of labeled osteocytes throughout the bone cross-section. However, previous long-term experiments using a similar loading preparation had consistently shown the site of most periosteal new bone formation to also not be directly related to the local strain magnitude. Perhaps it is significant that the greatest percentage of labeled cells were found in the cortex where the long-term experiments had shown most new bone formation to subsequently occur.

Exercise: A Prevention and Treatment for Osteoporosis and Injurious Falls in the Older Adult

“…Six hours after loading, radioactive osteocyte RNA was significantly increased in the loaded cores compared to unloaded cores. Pead, Suswillo, Skeny, and Lanyon (1988) showed that a single period of loading resulted in the transformation of quiescent lining cells into active osteoblasts within 5 days of the load stimulus.…”

Mechanosensory responses of osteocytes to physiological forces occur along processes and not cell body and require α V β 3 integrin

“…intracellular calcium | cell process attachment | fluid flow activation | purinergic signaling A dynamic and complex structure such as bone has the ability to adapt and to adjust to changes in its functional environment. Emerging evidence suggests that osteocytes play an important role in regulating bone mechanoadaptation and in adjusting and maintaining bone mass (1)(2)(3)(4)(5)(6). Osteocytes, which account for ∼90% of the entire bone cell population, are viewed as the main mechanosensing cells that detect whole tissue mechanical loading due to their unique distribution throughout the mineralized matrix and to their connection to the neighboring osteocytes and osteoblasts via gap junctions (7).…”

“…The authors declare no conflict of interest. 1 To whom correspondence may be addressed. E-mail: weinbaum@ccny.cuny.edu or mia.thi@einstein.yu.edu.…”

Endogenous mediators of growth

“…What is not clear at present is the mechanism of response to loading, although recent evidence suggests a possible role for the osteocyte (Pead et al 1988). …”

“…This remodelling process is also important in intramembranous (skull growth) and endochondral bone formation during bone development and growth. The osteocyte, which is an osteoblast embedded in the matrix, is probably responsible for sensing the changes in mechanical demand (Pead et al 1988). …”