Effects of Growth Hormone Receptor Antagonist Treatment on Metabolic Response and Performance in Young Men

Abstract

PURPOSE: We examined the effects of growth hormone receptor (GHR) antagonist treatment on metabolic response and performance. METHODS: Twenty healthy young men were assigned to either GHR antagonist treatment (n=10, 25 + 1 yrs, 184 + 2 cm, 80 + 5 kg) or placebo treatment group (n=10, 23 + 1 yrs, 182 + 2 cm, 81 + 5 kg). The subjects received either GHR antagonist (somavert, 10 mg daily by sc injection) or placebo for 16 days (every second day). After the treatment period, they performed 60 min of submaximal bicycling (55-70% of VO2max) followed by all-out exercise at 90% of VO2max. Blood and respiratory gas were collected at rest, during exercise and post-exercise. RESULTS: Baseline data showed no difference in VO2max between the groups (Treatment: 43 + 2, Placebo: 43 + 2 ml/min/kg). After the treatment period, the VO2max and maximal heart rate did not change in both groups. Oxygen uptake, and fat oxidation pattern (estimated by respiratory exchange ratio) showed no significant change after the treatment period in both groups. On the other hand, the ratings of perceived exertion (RPE) during the exercise were significantly higher in the treatment group compared to in the placebo group (P < 0.05). The treatment group showed higher lactate concentration during the last 30-min of exercise. In the placebo group, all subjects completed the 60-min of submaximal exercise. However four subjects in the treatment group could not finish the whole exercise protocol. Time to exhaustion during the all-out exercise was shorter in the treatment group (67 + 33 s) compared to in the placebo group (131 + 33 s) although no statistical difference was observed. CONCLUSIONS: These results indicate that GHR antagonist treatment exaggerates fatigue during exercise and reduces time to exhaustion, suggesting a possible role of GH in exercise performance.