The Emerging Role of the Endocannabinoid System in Endocrine Regulation and Energy Balance

The Emerging Role of the Endocannabinoid System in  Endocrine Regulation and Energy Balance

Uberto Pagotto, Giovanni Marsicano, Daniela Cota, Beat Lutz, and Renato Pasquali

Endocrinology Unit, Department of Internal Medicine and Gastroenterology, and Center for Applied Biomedical Research (U.P., R.P.), Sant’ Orsola-Malpighi Hospital, 40138 Bologna, Italy; Department of Physiological Chemistry (G.M., B.L.), Johannes Gutenberg-University Mainz, 55099 Mainz, Germany; and University of Cincinnati, Department of Psychiatry, Obesity Research Center, Genome Research Institute (D.C.), Cincinnati, Ohio 45237

Abstract:
 
During the last few years, the endocannabinoid system has emerged as a highly relevant topic in the scientific community. Many different regulatory actions have been attributed to endocannabinoids, and their involvement in several pathophysiological conditions is under intense scrutiny. Cannabinoid receptors, named CB1 receptor and CB2 receptor, first discovered as the molecular targets of the psychotropic component of the plant Cannabis sativa, participate in the physiological modulation of many central and peripheral functions. CB2 receptor is mainly expressed in immune cells, whereas CB1 receptor is the most abundant G protein-coupled receptor expressed in the brain. CB1 receptor is expressed in the hypothalamus and the pituitary gland, and its activation is known to modulate all the endocrine hypothalamic-peripheral endocrine axes. An increasing amount of data highlights the role of the system in the stress response by influencing the hypothalamic-pituitary-adrenal axis and in the control of reproduction by modifying gonadotropin release, fertility, and sexual behavior.

The ability of the endocannabinoid system to control appetite, food intake, and energy balance has recently received great attention, particularly in the light of the different modes of action underlying these functions. The endocannabinoid system modulates rewarding properties of food by acting at specific mesolimbic areas in the brain. In the hypothalamus, CB1 receptor and endocannabinoids are integrated components of the networks controlling appetite and food intake.

Interestingly, the endocannabinoid system was recently shown to control metabolic functions by acting on peripheral tissues, such as adipocytes, hepatocytes, the gastrointestinal tract, and, possibly, skeletal muscle. The relevance of the system is further strenghtened by the notion that drugs interfering with the activity of the endocannabinoid system are considered as promising candidates for the treatment of various diseases, including obesity. 
 
 
Introduction

THE FIRST STEPS in the discovery of the endocannabinoid system date back almost 4000 yr, when the therapeutic and psychotropic actions of the plant Cannabis sativa were first documented in India (1). Over the last 40 yr, after Gaoni and Mechoulam (2) purified the psychoactive component from hemp, a stunning amount of research has revealed the endocannabinoid system as a central modulatory system in animal physiology. Elements of the endocannabinoid system comprise the cannabinoid receptors, the endogenous lipid ligands (endocannabinoids), and the machinery for their biosynthesis and metabolism (3, 4). Despite public concern related to the abuse of marijuana and its derivatives, the research on the endocannabinoid system has recently aroused enormous interest not only for the physiological functions, but also for the promising therapeutic potentials of drugs interfering with the activity of cannabinoid receptors. This review aims to provide an overview on the pivotal role of the endocannabinoid system in the modulation of the neuroendocrine and peripheral endocrine systems. Moreover, in the context of the recently proposed therapeutic applications of cannabinoid receptor antagonists in the treatment of obesity, the key role of the endocannabinoid system in the control of eating behavior, food intake, and energy metabolism will be discussed in the light of the recent data obtained from human and animal studies.
 
 
Endocrine Reviews is published by The Endocrine Society (http://www.endo-society.org), the foremost professional society serving the endocrine community.