[Leptin, insulin and proinsulin--their relationship]

Leptin is protein produced by mature adipocytes into the system circulation and gives information to hypothalamic centers about fat amount in the organism. Leptin is supposed to play a causal role in energy output of the organism and influences the appetite (antiobese effect). Obese individuals were proved to have frequently hyperleptinemia. This disease is caused by a postreceptor disorder (however, several obese families had also normoleptinemia or even hypoleptinemia which is caused by polymorphism of Ob-gene). It was also found that leptin administration in animals leads to reduced appetite and decreased body weight. Interpretation of leptinemia in human is very complicated because leptinemia is influenced by many independent regulations (hormones, stress, food intake, motor activity atc.). Obesity is often associated with hyperinsulinemia and insulin resistance (a frequent cause of human mortality) so that correlations between insulin and leptin are intensively studied. Experimental models and animal studies revealed the existence of adipoinsular axis and it was found that insulin and leptin are contrahormones. In human studies, the majority of authors did not find correlation between leptinemia and markers of insulin secretion. Similar conclusions were drawn out in our previous paper [118]. This may be due to complex regulations of leptinemia in the organism and the use of biochemical markers with limited validity (insulin, C-peptide in fasting state and after stimulation). Therefore we decided to study correlation between leptinemia and intact proinsulin in the serum which is now considered to be the most valid marker of insulin secretion and provides information about an average "daily" insulinemia. This study was stimulated by the fact that increased leptinemia is found also in persons with prolonged hyperinsulinemia (a short-term hyperinsulinemia does not affect leptin concentration so that no available marker of insulin secretion is valid). We examined the group of 31 probands, patients of the Metabolic and Diabetologic Center at the hospital in Sternberk. They were diabetic patients of type 2 who were treated by peroral antidiabetics and insulin and who met criteria of good compensation. However, no correlation between leptinemia and proinsulinemia was found. We suppose that this failure was due to complicated fine regulations affecting leptinemia and also to the fact that intact proinsulin is not an "ideal" marker of a long-term hyperinsulinemia (correlation between insulin and leptin at euglycemic clamp indicates that there exist correlation between these parameters in human).