The Havers-Halberg oscillation and bone metabolism

Introduction Rather than being a passive responder to other body tissues, bone is a dynamic participant in overall homeostasis, with a major impact on how other tissues behave throughout ontogeny. Bones act as endocrine organs to regulate metabolic rate and cell function in cooperation with adipose tissue, the hypothalamus and pituitary, thyroid, pancreas, and a number of other organs besides (e.g., Confavreaux et al., 2009). In an evolutionary sense, this means that the study of bone histology and physiology should give us fundamental information about evolution of energetics (how individual organisms use available calories) and life history (patterns of growth, reproduction, and lifespan). On the flipside, more information about energetics and metabolic physiology will greatly inform our understanding of skeletal growth processes. Following this concept, we have recently advanced a hypothesis that the physiological keystone between the bone/energy complex is a biorhythm centered in the hypothalamus of the brain, known as the Havers-Halberg Oscillation (HHO; Bromage et al., 2009). To summarize, this hypothesis argues that a biological clock within the hypothalamus influences metabolism, cell proliferation, and other life history variables through oscillations in output via sympathetic neurons. This biorhythm impacts the growth of bone, such that we can see recorded signatures of it within bone histology (and within teeth). To date, there has been no synthesis of the major concepts linking the physiology of bone to the physiology of energy homeostasis, with regard to the work of prior researchers that was used to build the HHO model. Likewise, there is no synthesis of the data supporting the HHO model to date, and no evidence published with regard to bone’s tissue-specific metabolic rate in order to discuss how the HHO affects bone specifically within the context of the entire organism. This chapter is intended to (1) provide a review of the bone/energy homeostasis literature in light of the HHO; (2) to summarize the HHO research that has been performed thus far and examine how this mechanism impacts the growth of bone such that we can see recorded signatures of it within bone histology (and within teeth); and (3) present new evidence with regard to bone’s tissue-specific metabolic rate.