ABSTRACT
Introduction ....................................................................................................................................105 Discovery of Ghrelin......................................................................................................................106 Structure of Ghrelin and Its Functional Receptor, GHS-R...........................................................106 Distribution and Biological Functions of Ghrelin: An Overview.................................................107 Ghrelin and the Control of Appetite: Major Effects and Mechanisms of Action ........................108 Regulation of Ghrelin Levels and Interaction with Leptin System..............................................109 Ghrelin as a Neuroendocrine Integrator Linking Energy Status and Other Key Functions ........111 Major Conclusions and Future Perspectives .................................................................................111 Acknowledgments ..........................................................................................................................112 References ......................................................................................................................................112
Homeostatic control of energy balance is a key biological function essential for the survival of individuals and species. Maintenance of the energy status of an organism critically relies on the dynamic balance between energy expenditure and food intake. In this equation, expression of appetite (defined as the motivational drive toward an energy source) appears as a pivotal, highly regulated phenomenon, based on the complex physiological interaction of afferent signals (which promote or inhibit appetite) and effector mechanisms (which restrain or get into motion the drive toward food intake). Among the former, multiple peripheral factors, arising mostly from the adipose tissue, pancreas, and gastrointestinal tract, have been identified in the last decades as powerful regulators of central circuits at the hypothalamus, as well as in the brainstem and limbic system. At those sites, such factors actively modulate neuropeptide release and, thereby, participate in the control of food intake and energy expenditure [1,2].
