As an endocrine organ, the fatty tissue secretes a variety of hormones, which are called adipokines. In severely overweight individuals, the adipocyte function is deregulated and the production of adipokines changes with regard to their amount. Adiponectin and leptin are the most common adipokines and represent the link at the level of signal transduction between adipositas and metabolic disorders.
Adiponectin is present in the plasma in high concentrations. The adiponectin expression is downregulated in the fatty tissue of obese persons; the values in obese humans (fat and serum) are lower than in persons of normal weight. Adiponectin is insulin-sensitising and anti-inflammatory, and protects from atherosclerosis.
Leptin suppresses the appetite and increases the energy usage and weight loss under normal physiological conditions. The leptin level in the blood correlates with the amount of fat and increases in adipositas, which suggests that obese persons have a leptin resistance. Its concentration is decreased in hunger and malnutrition. Leptin is a pro-inflammatory adipokine.
A connection between insulin and leptin levels has been observed in patients with diabetes mellitus type 2 (DMT2). Low adiponectin and increased leptin levels in adipositas cause a chronic weak inflammatory status, which promotes the development of insulin resistance and DMT2, high blood pressure, atherosclerosis and other cardiovascular diseases.
Low adiponectin and increased leptin are independent risk factor for the metabolic syndrome.