The Ghrelin Response to Exercise before and after Growth Hormone Administration

Abstract

Abstract Context: We have previously shown that exercise-induced GH release is not mediated by ghrelin, but it remains to be studied whether the increase in GH may suppress postexercise ghrelin levels. Objective: The objective of this study was to characterize systemic ghrelin levels after exercise with and without concomitant GH administration. Design, Participants, and Intervention: Group A: Twenty-nine elite athletes (age, 18–37 yr) were studied after a maximal exercise test. Group B: In a double blind, placebo-controlled, parallel study, 32 healthy subjects (age, 18–33 yr) were randomized to placebo, GH 0.1 IU/kg per day, or GH 0.2 IU/kg per day for 4 wk. These subjects performed a multistage fitness test to assess maximum oxygen uptake at baseline and after 4 wk. We measured total circulating ghrelin levels before and immediately after exercise and at 15, 30, 60, 90, and 120 min after exercise. Results: Group A: Serum ghrelin levels after exercise decreased significantly (P < 0.01). Group B: Exercise at baseline was associated with a significant lowering of ghrelin levels after exercise (P < 0.0001). In addition, 4 wk of high-dose GH were followed by a further approximately 20% reduction in basal and after exercise serum ghrelin (micrograms per liter): 0.78 (range 0.52–1.17) vs. 0.63 (range 0.50–0.91), P < 0.05. Conclusions: 1) Ghrelin levels decrease significantly after exercise in elite athletes and healthy subjects. 2) High-dose GH suppresses ghrelin levels. 3) These data support the hypothesis that GH feedback inhibits ghrelin secretion.