Fat as an endocrine organ: influence of exercise
Journal of applied physiology
The prevalence of diabetes and obesity continues to increase. It is therefore important to identify the pathophysiology underlying these disorders. An inability of insulin to stimulate glucose uptake, i.e., insulin resistance, appears to be a common link between diabetes and obesity. The identification of various adipocyte-secreted cytokines (adipocytokines) that influence satiety, energy balance, and insulin sensitivity provide a novel target for the treatment of these disorders.
... are differentially expressed with obesity and diabetes, making them a strong candidate for linking insulin resistance to these pathological conditions. This review explores the role of adipocytokines in insulin action and examines the effect of exercise training on adipocytokine content. adipocytokines; insulin sensitivity; metabolism ALTHOUGH ONCE THOUGHT TO BE a mere storage depot of excess energy, it is now apparent that adipose tissue is an endocrine organ and plays a prominent role in energy metabolism. The discovery of leptin, a satiety hormone secreted by adipose tissue, led us to change the way we view the role of adipose tissue in nutrient metabolism. In addition to leptin, other cytokines including tumor necrosis factor (TNF)-␣, interleukin-6 (IL-6), resistin, visfatin, acylation stimulation protein, and adiponectin have been identified as adipose-secreted proteins that are collectively referred to as adipocytokines. Adipocytokines have numerous functions that include regulation of satiety, carbohydrate and lipid metabolism, and insulin sensitivity. They are differentially expressed with obesity and diabetes. Metabolic syndrome is characterized as a cluster of metabolic conditions including excess abdominal fat, hyperglycemia, hyperlipidemia, and hyperinsulinemia (75). Peripheral insulin resistance appears to be the common mediator of altered nutrient metabolism observed in these disorders. Because adipocytokines have been shown to influence insulin signaling, regulation of these cytokines may play a role in the etiology of insulin resistance, obesity, and diabetes by altering or influencing carbohydrate and/or lipid metabolism. The study of these novel proteins is important as the prevalence of metabolic syndrome, diabetes, and obesity are increasing at epidemic rates and represent a large portion of health care costs. Weight reduction and exercise are common nonpharmaceutical interventions for the treatment of insulin resistance. Exercise may improve insulin sensitivity by modulating the plasma content and/or function of adipocytokines. Therefore, this review will focus on the following topics: 1) what are the roles of adipocytokines in skeletal muscle substrate metabolism and 2) what effect does exercise have on circulating levels of adipocytokines? ADIPOCYTOKINES, INSULIN RESISTANCE, DIABETES, AND OBESITY