Thomas Graves, DVM, PhD, Diplomate ACVIM & Debra L. Zoran, DVM, PhD, Diplomate ACVIM (Small Animal Internal Medicine)
Tuesday, January 20 • 9:00-9:50, Gaylord
Adipocytes secrete over 50 adipokines that act to control various metabolic and endocrine functions. Adiponectin and leptin, 2 of the many adipokines secreted, are extremely important hormones that have both central and peripheral effects on metabolism and energy balance. Adiponectin enhances insulin sensitivity in both muscle and liver tissues and increases oxidation of free fatty acids (FFAs) in several tissues, including muscle. In normal lean mice, adiponectin also decreases serum FFAs, glucose, and triglyceride concentrations. Leptin influences food intake and energy expenditure. In the normal lean animal, increased leptin secretion from adipocytes is a key satiety signal that reduces intake after meals. As adipocytes enlarge due to increasing obesity, the adipose tissue itself undergoes molecular and cellular alterations that affect the adipokines themselves as well as their influence on metabolism. First, with increasing obesity, there is an increase in whole-body FFA levels and glycerol release from adipocytes, which is known to promote insulin resistance. Second, with increasing adiposity, a number of proinflammatory cytokines are produced in white adipose tissue. These proinflammatory cytokines, which include tumor-necrosis factor α, interleukin 6, nitric oxide synthetase, transforming growth factor, plasminogen-activator inhibitor, and monocyte chemotactic protein, are not present in normal adipose tissue but increase steadily with increasing adiposity. Numerous diseases in dogs and cats are reported to be associated with obesity, including orthopedic diseases, diabetes, heart disease, abnormal circulating lipids, certain types of cancer, urethral sphincter mechanism incompetence, dyspnea due to compromised ability to breathe, heat intolerance, decreased immune function, and dystocia. In dogs and cats, neutering affects levels of leptin, progestins, and other hormones, resulting in an increased appetite and reduced energy metabolism and metabolic rate. The key factors for prevention of obesity in neutered animals appears to be careful control of intake immediately after neutering and close monitoring of body weight and body condition score to allow adjustments in intake if needed.
COMMENTARY: Obesity has long been recognized as a contributor to increased risk for morbidity in dogs and cats. However, as this presentation highlights, only recently have we come to understand the extensive endocrine role of white adipose tissue. This article presents an overview of metabolic, physiologic, and endocrine changes that occur in obesity, providing an even more compelling rationale for addressing this condition in companion animals.