Urinary insulin-like growth factor-I measurement in an actual sport competition, an additional approach in laboratory antidoping tests

Abstract

Background The insulin-like growth factor hormone (IGF-I) is an important protein hormone under investigation with physical exercise and for doping detection. Urinary IGF-I level in fact represents a relevant measurement when the postexercise proteinuria is under analysis. To verify the IGF-I level variation in the circulation and in urinary excretion in the occasion of a competition, the plasma and urine IGF-I in athletes before and after an actual competitive event were measured. Methods Twenty well-trained cyclists took part in a competition (102 km) and concluded the intense physical exercise in approximately 2 1/2 h. Urine and blood samples were collected from each athlete 10–20 min before and at the end of the competition. Plasma and urine total IGF-I (pIGF, uIGF), total urinary proteins (uPr), and creatinine (uCr) concentrations were measured. Results The uIGF [from 76.2±15.8 to 256.9±29.1 ng/l ( p<0.001)], uPr [from 29.4±6.7 to 325.9±95.1 mg/l ( p<0.005)], and uCr [from 6.3±1.0 to 10.0±0.8 mmol/l ( p<0.005)] significantly increased. The pIGF was 262.6±14.3 and 247.3±11.8 μg/l before and end-exercise, respectively. A statistical correlation between uIGF and uPr was demonstrated ( p<0.001). The pIGF/uIGF ratio was significantly ( p<0.05) decreased comparing the end with before the competition. Conclusions The pIGF/uIGF significantly decreased at the end, compared with before the competition, suggesting a changed uIGF excretion. This increment appeared to be increased, although not significantly, considering the ratio with uCr.