Physiology of the Adrenal and Liver Circadian Clocks

In most organisms, various aspects of physiology and behavior, including metabolic, endocrine and immune functions, show circadian rhythms that are governed by endogenous molecular clocks. The hypothalamic suprachiasmatic nuclei (SCN) are considered as a central circadian pacemaker that receives light input directly from a specific subpopulation of photosensitive ganglion cells in retina and transmits this information downstream to synchronize single cell oscillators in various tissues. The recent development of genetic tools allowing tissue-specific deletion of clock genes has provided new insight into the contribution of peripheral clocks to the regulation of physiological rhythms. This chapter describes the circadian physiology of two organs involved in metabolic regulation and energy homeostasis: liver and adrenal gland. Both tissues harbor robust circadian clocks that possess partial autonomy from SCN. The chapter discusses the functions of these oscillators, potential communication routes between them and the SCN, and how their disturbance may promote development of diseases.