Leptin (Lept; Greek: leptos = thin) is a satiety hormone synthesized (produced) mainly by adipocytes (“fat cells”). Serum leptin levels correlate positively with body fat mass (KFM) and BMI (body mass index – also called body mass index (BMI)). It is also produced in small amounts in the placenta (placenta) the mammary epithelium, bone marrow, skeletal muscle, pituitary gland (pituitary gland) and hypothalamus (section of the diencephalon).
Leptin transmits a satiety signal, centrally down-regulating food intake (hunger) and increasing energy expenditure. It has an antagonistic function to ghrelin (acronym for Growth Hormone Release Inducing). Ghrelin is synthesized in the gastric mucosa and is an appetite-stimulating hormone. It regulates food intake and also the secretion of growth hormone. During periods of hunger, the level of ghrelin in the blood increases, and after eating it decreases. Lack of sleep leads to increased ghrelin secretion.
In the case of leptin deficiency (lack of leptin) or leptin resistance (“reduced response to leptin”), the effect of the central satiety signal is disturbed, i.e. food intake is increased. As a result, endocrine-induced obesity (hormone-induced overweight) develops with insulin resistance (reduced response of the body’s cells to the hormone insulin).
Another function of leptin is the regulation of glucose homeostasis (maintenance of a state of equilibrium of the glucose serum level; here: Glucose-lowering effect) and improving insulin sensitivity in muscle tissue and the liver.
The procedure
Material needed
- Serum
Normal values
| BMI | Women | Men |
| 18-25 | ≤ 24.0 ng/ml | ≤ 10.0 ng/ml |
| 26-29 | 6.0-50.0 ng/ml | 1.00-23.0 ng/ml |
| 30-35 | 11.0-121 ng/ml | 3.00-70.0 ng/ml |
| 36-37 | 25.0-141 ng/ml | 12.0-135 ng/ml |
Reference values differ depending on the radioimmunoassay (RIA) used.
Indications
- Early and severe obesity (overweight).
Interpretation
Interpretation of increased values
- Obesity with hyperleptinemia (elevated leptin levels) with central and/ or peripheral leptin resistance → hyperphagia (binge eating) [typical circumstance].
Interpretation of decreased values
- Leptin deficiency (leptin deficiency) → hyperphagia → morbid obesity (obesity per magna; BMI ≥ 40) and hyperglycemia (hyperglycemia) [very rare!].
Further notes
- In case of extreme obesity in childhood, a mutation of the leptin receptor must be considered.
- Reducing body weight (or body fat weight) or therapy with glitazones (“insulin sensitizers”) will lower serum leptin levels.
