Determination of inter-day variations in hGH markers in athletes

Code: T04B8AK

Human growth hormone (hGH) is assumed to be abused as an anabolic hormone among athletes to enhance their physical performance. Several methods to detect hGH doping are under development, among others the “Marker approach”. Application of hGH effectuates a number of processes in the organism, which can lead to changes in the concentration of peptides and proteins. Some of these parameters measurable in serum are insulin-like growth factor I (IGF-I), acid labile subunit (ALS), IGF-binding protein-3, N-terminal propeptide of the type III procollagen (PIIINP), crosslinks (ICTP) and osteocalcin. The concentration of these markers vary inter-individually. Therefore it is impossible to discriminate between treated and untreated athletes using only one of these markers. As a consequence, it is necessary to calculate a discriminant function combining some of these parameters. As a result of our hGH application study with 15 athletes, we published recently a discriminant function which separated hGH-treated and placebo-treated subjects clearly. On the other hand there are indications that some markers are influenced by physical activities. As shown in some studies, acute physical stress influences the levels of these markers not very strong and only temporarily, but there are no data concerning the effects on long-term variation in physical stress (e.g. changes in intensity, category of physical activity, intermission and restart of training) on the parameters until now. The proposed study will give information about the long-term intra-individual variations of hGH markers and about the effects of long-term changes in physical activities on the hGH marker level.

Main Findings

For more than ten years intensive efforts have been made to develop the “marker approach” for detecting hGH doping. Due to the fact that exogenous and endogenous hGH are nearly identical and the metabolic half live of hGH is only 20 – 30 min, the search for a marker based method is reasonable.

From the vast number of GH-dependent peptides the insulin-like growth factor I (IGF-I) and the N-terminal pro-peptide of type III procollagen (PIIINP) seem to be the most promising markers for usage in doping analysis at the moment. Both markers are mainly GH-regulated and less sensitive to the acute effects of exercise. On the other hand in both markers the magnitude of the response to exogenous hGH and the concentration at baseline vary widely inter-individually.

Factors influencing these markers have been investigated in extensive studies (e.g. acute physical stress, differences between normal subjects and athletes, illnesses, injuries, different sports, medication, ethnicity).

Several studies tried to define age-dependent cut-off levels for the marker concentrations in athletes; however the ranges of these limits are very wide because of the enormous inter-individual variation.

Congruously, it seems to be reasonable to establish profiles of athletes including the marker concentrations of each subject to reveal possible manipulations. However for the evaluation of such profiles a thorough knowledge concerning the actual intra-individual fluctuation ranges and possible influences to these markers are indispensable.

It is known that both IGF-I and PIIINP show no diurnal variation and have a good long-term stability of their concentrations in normal subjects. However, only few investigations exist concerning the effects of deep changes in the intensity or category of heavy physical stress.

In this context the aim of the present study was to evaluate the long-term stability of IGF-I and PIIINP concentrations in high level athletes with special respect to changes in the intensity of the training workload.

Fifty male and female athletes (all Caucasians; 31 f; 19 m, 19,3 +/- 3,2y) were included in the study performing at least six intensive training sessions per week in different sports. Eight blood samples were taken from each subject over a period of 18 months with an interval of at least 4 weeks between each sampling, with special respect to changes in the training intensity and overall physical strain of the athletes.

IGF-I and PIIINP concentrations were determined in all serum samples using immunoassays.

About fifteen percent of the samples had IGF-I and PIIINP concentrations above the upper limits of the 95 % age dependent reference ranges specified by the manufacturer. The IGF-I concentrations did not differ significantly between male and female athletes; PIIINP levels in male subjects were significantly higher than in females.

As expected, there was a wide variation of the IGF-I and PIIINP levels between the athletes independent from age, reflecting the inter-individual variability of the marker.

The intra-individual variability of the IGF-I and PIIINP concentration was in female considerably higher than in male subjects. Partly, the fluctuations exceeded significantly the expected level. In single cases changes in the marker concentrations could be associated with changes in the workload level. The influence of the performed sport discipline couldn’t be proven, as the sports were not uniformly distributed among the gender.

Summarizing the study revealed unexpected high fluctuations in the hGH marker concentrations in high level athletes. The adaptation of the body to heavy physical stress caused by strong changes in intensity and category of the training workload can be observed in alterations of the marker levels.