The Mechanisms and Physiological Consequences of Diurnal Hepatic Cell Size Fluctuations: A Brief Review.

Liver size in mammals fluctuates throughout the day and correlates with changes in hepatocyte size. However, the role of these daily changes in liver and hepatocyte size and the underlying molecular mechanisms remain largely unknown. In this review, we highlight the view that hepatocyte size, and thus, overall organ size, is subject to regulation by the circadian clock and feeding/fasting cycles. To that end, we provide an overview of the current literature dealing with this phenomenon and elaborate the role of feeding and nutrients in this process. We will discuss the role of hepatic protein content and synthesis, which are both subject to diurnal regulation, in daily hepatocyte and liver size fluctuations. Although there is evidence that changes in hepatocyte and liver size are associated with daily variations in macromolecule content, there is also evidence that these changes in size may be actively regulated by modifications of the cells' osmotic environment. Future research will need to examine the intriguing possibility that hepatocyte and liver size fluctuations may be required for normal liver function and to reveal the underlying molecular mechanisms behind this process.