Growth Hormone Concentrations in Different Body Fluids Before and After Moderate Exercise

Growth hormone (GH) has many direct and indirect actions and roles including substrate regulation and priming of some cells of the immune system, and the expected aspects of growth and repair. Different concentrations in human body fluids reflect the exercise-induced growth hormone response (EIGR) after exercise. In populations such as elite athletes, the invasive nature of venous sampling is poorly accepted. Thus, this study examines possible viable alternatives such as urine and saliva samples and the GH concentration.

A heterogeneous group of 11 males (age 26.0 ± 5.0 years; body mass 76.5 ± 9.3 kg; VO_2peak 57.0 ± 6.0 mL kg^-1 min^-1) ran for 40 min on a treadmill at 5 % below their individually indentified lactate threshold pace. Samples of urine, saliva and blood were collected immediately pre- and post-test and at 30 and 60 min post-test.

Salivary GH was correlated with serum pre- and post-exercise (p < 0.001); urinary GH was correlated with serum (p < 0.05). However, despite being significantly correlated, it is clear from the large differences in absolute concentration in the three media that the appearance of serum GH due to exercise is different from that of the appearance of salivary and urinary GH. This aspect of compartmental exchanges is very difficult to define and to investigate. Differences in any analyte concentration in different compartments are to be expected between different media, and hence the same medium should be used where the same 'pattern of response' can be tracked.

The results suggest that urinary and saliva sampling cannot substitute for venous sampling with respect to exercise-induced changes in GH concentration. The use of the analyses in these three areas may be appropriate for further investigation.