Measurement of free IGF-I saliva levels: Perspectives in the detection of GH/IGF axis in athletes

Objectives: To examine an immunoassay for measuring free IGF-I in a saliva specimen (free sIGF-I) and to study the levels in relation to the training conditions comparing young athletes and sedentary females. Design and methods: The analysis was carried out by modifying a commercial kit for plasma matrix to measure the free sIGF-I. The plasma free and total IGF-I fractions, hGH and salivary total proteins were also measured. Saliva and blood specimens were collected from 15 well-trained young female volleyball athletes and from a control group of 14 young sedentary females. Results: The calibration curve to assay free sIGF-I covered the range 0.05–5.00 μg/L. The detection limit was 0.07 μg/L. The within-run and between-run imprecision CVs were 10% and 13% respectively. The average recovery was 88%. Free sIGF-I, measured in 15 athletes and in 14 young sedentary females, was 0.10 ± 0.03 and 0.20 ± 0.05 μg/L respectively (p < 0.001). Conclusions: There were decreased levels of free sIGF-I in well-trained athletes, compared with sedentary females. This decrease could be related to a greater tissue requirement by the active muscle subjected to intense exercise for several days.