Fig. 3. Peripheral clock output.

The core clock machinery has been identified in most peripheral tissues. In addition, rhythmic gene expression appears to be regulated in a tissue-specific manner, enabling each tissue to appropriately calibrate local physiological processes within the appropriate overall temporal schedule. However, circadian disruption either within or amongst individual tissues may lead to organ dysfunction. Indeed, recent studies suggest that peripheral clock alteration is involved in body weight gain as well as abnormalities in glucose homeostasis and blood pressure regulation, thereby contributing to the development of the metabolic syndrome. These alterations may be initiated by disruptions in circadian behavioral and/or environmental factors such as high-fat diet. Circadian and physiological systems are interconnected through reciprocal feedback loops within each tissue locale.