Leptyna
Leptin is a 167 amino acid protein encoded by the ob gene. The leptin molecule is structurally similar to the pro-inflammatory molecules – cytokines. Leptin is produced and secreted mainly by mature cells of adipose tissue. Its production in small amounts also occurs in the stomach, skeletal muscles, liver and brain. Leptin acts in the body through specific receptors located in the hypothalamus and in peripheral tissues. Peripheral leptin receptors are ubiquitous and soluble leptin receptor circulating in serum has been identified. In lean people, most of the circulating leptin is in the form bound to a soluble receptor, while in obese people free leptin predominates. Leptin concentration is directly proportional to the body mass index (BMI) and the size of fat cells. Since leptin levels are clearly elevated in obese people, leptin can be considered a marker of obesity and obesity-related diseases. Leptin is essential for maintaining the body’s energy homeostasis, but its correct or even increased concentration does not always ensure proper functioning due to the phenomenon of leptin resistance, which may underlie many disorders. Under physiological conditions, a reduced concentration of leptin seems to play a more important role as a signal needed to save energy in the conditions of a negative balance and reduced energy reserves, and not increased concentrations of this adipokine as a mechanism preventing obesity, signaling a positive energy balance and increased reserves. For this reason, it is believed that low leptin levels are one of the signals that stop menstrual cycles in women with anorexia nervosa, or in athletes with a very low body fat content. At the same time, it is believed that stopping the menstrual cycles may constitute a specific protective mechanism that turns off reproductive activities when the content of energy reserves (adipose tissue) in the body of a potential mother is too low. Insulin resistance is accompanied by low concentrations of the soluble leptin receptor (which acts as the binding protein for free leptin) and low values of the ratio between bound and free leptin. This phenomenon has also been observed in patients with metabolic syndrome. There are also reports that the administration of leptin may reduce insulin resistance and improve the lipid profile in a mechanism independent of the reduction of body weight, associated with the reduction of lipid accumulation in muscle cells, with the intensification of fatty acid oxidation in skeletal muscles, and with a decrease in gluconeogenesis and hepatic insulin resistance.
Source: A. Cajdler-Łuba, S. Mikosiński, A. Sobieszczańska-Jabłońska, I. Nadel, I. Salata, A. Lewiński: “FUNCTIONAL DIAGNOSTICS OF HORMONAL DISORDERS WITH ELEMENTS OF DIFFERENTIAL DIAGNOSTICS; Czelej Publishing House