Hormonal Regulation of Energy Balance and Energy Stores

Abstract

Adipose tissue sits at the crossroads of metabolism. It actively participates in the day-to-day regulation of energy balance, and it is the largest reservoir of energy for long-term needs. The human body is designed to sense its current energy status. Fuel sensors are located in the abdominal cavity along the digestive tract but also in adipose tissue. Afferent signals from these sensors reach the central nervous system in the form of neural and hormonal inputs. The brain directs action to maintain a steady intake of nutrients and energy.

An overarching principle is that there are regulatory and counter-regulatory systems which are constantly operating, and the ratio of them is what determines the outcome. An example of this is the ratio of insulin to glucagon in the venous drainage of the pancreas, which determines the response of the liver acutely. Another example is the leptin to adiponectin ratio in the venous drainage of intra-abdominal (visceral) adipose tissue, which signals the liver and brain on the status of energy stores and adipose tissue function.

Constant fuel signaling allows the body access to nutrients. When access to nutrients is not possible, the body engages metabolic pathways to compensate. Long-term derangements of fuel acquisition cause profound alterations in the signaling pathways and allow the body to survive longer. Both anorexic diseases at one extreme and obesity on the other are characterized by changes from normal physiology. In the case of obesity, for example, there is a significant rise in the leptin to adiponectin ratio. This signals the brain that there are excess calories in storage and that adipose tissue function is compromised. Understanding these metabolic relationships allows for the development of targeted treatments for chronic diseases of metabolism.