The endocrine function of adipose tissue: an update

Adipose tissue secretes bioactive peptides, termed 'adipokines', which act locally and distally through autocrine, paracrine and endocrine effects. In obesity, increased production of most adipokines impacts on multiple functions such as appetite and energy balance, immunity, insulin sensitivity, angiogenesis, blood pressure, lipid metabolism and haemostasis, all of which are linked with cardiovascular disease. Enhanced activity of the tumour necrosis factor and interleukin 6 are involved in the development of obesity-related insulin resistance. Angiotensinogen has been implicated in hypertension and plasminogen activating inhibitor-1 (PAI-1) in impaired fibrinolysis. Other adipokines like adiponectin and leptin, at least in physiological concentrations, are insulin sparing as they stimulate beta oxidation of fatty acids in skeletal muscle. The role of resistin is less understood. It is implicated in insulin resistance in rats, but probably not in humans. Reducing adipose tissue mass, through weight loss in association with exercise, can lower TNF-alpha and IL-6 levels and increase adiponectin concentrations, whereas drugs such as thiazolinediones increase endogenous adiponectin production. In-depth understanding of the pathophysiology and molecular actions of adipokines may, in the coming years, lead to effective therapeutic strategies designed to protect against atherosclerosis in obese patients.