Responses of the growth hormone (GH) and insulin-like growth factor axis to exercise, GH administration, and GH withdrawal in trained adult males: A potential test for GH abuse in sport

GH abuse by elite athletes is currently undetectable. To define suitable ma rkers of GH doping, we assessed the effects of acute exercise, GH administr ation, and GH withdrawal on the GH/insulin-like growth factor (IGF) axis in athletic adult males. Acute endurance-type exercise increased serum GH, GH binding protein (GHBP), total IGF-I, IGF-binding protein (IGFBP)-3, and ac id-labile subunit (ALS), each peaking at the end of exercise. IGFBP-1 incre ased after exercise was completed. Free IGF-I did not change with exercise. Recombinant human GH treatment (0.15 IU/kg.day) for 1 week increased serum total IGF-I, IGFBP-3, and ALS, exaggerating the responses to exercise. IGF BP-2 and IGFBP-1 were trivially suppressed. After GH withdrawal, the GH res ponse to identical exercise was suppressed. Total IGF-I, IGFBP-3, and ALS r eturned to baseline over 3-4 days. In summary, 1) acute exercise transientl y increased all components of the IGF-I ternary complex, possibly due to mo bilization of preformed intact complexes; 2) GH pretreatment augmented the exercise-induced changes in ternary complexes; 3) postexercise IGFBP-1 incr ements may protect against delayed onset hypoglycemia; 4) serum total IGF-I , IGFBP-3, and ALS may be suitable markers of GH abuse; and 5) differences in disappearance times altered the sensitivity of each marker for detecting GH abuse.