Hormone de croissance et dopage : difficultés du dépistage

Abstract

Growth hormone and doping. Growth hormone (GH) plays a very important role in growth regulation as well as on the metabolism (protein, glucid and lipid). Its effects on cell proliferation and differentiation, essentially on cartilage cells, are mediated by hepatic (endocrine effect) and extra-hepatic (auto-paracrine effect) insulin-like growth factor I (IGF I). IGF I has, like GH, an anabolic action on protein metabolism, but opposite to GH, it has an hypoglycemic effect which is limited by specific binding proteins (IGFBP), including a GH-dependent one (IGFBP3). Whereas it is well-known that GH treatment has beneficial effects on body composition in GH-deficient patients (decrease in fat mass and increase in muscle mass), nothing has been demonstrated on doping effects in trained subjects, excepted perhaps to avoid protein catabolism. GH amounts used for doping might be largely supra-physiological and might potentiate other substances such as anabolic steroids. Adverse effects are not yet well described but seem potentially important at the vascular and tumoral levels. Recombinant human GH (rhGH) abuse in athletes is actually almost undetectable because rhGH has the same sequence than naturally-produced GH, with a very short biological half-life and important fluctuations in its plasma concentration. Moreover, GH secretion is modified by physical exercise. It is therefore needful to analyze GH concentration as well as secondary markers of its action (IGF I, IGFBP3, bone markers…). Reference values should be carefully established, taking into account not only age and gender, but also the type of physical activity and the level of training. Another direction in the detection of doping with GH should consider the measurement of other pituitary forms of GH than the most important GH 22 kD. For example the secretion of GH 20 kD is abolished in case of doping with rhGH.