The Ghrelin Response to Exercise before and after Growth Hormone Administration

Abstract

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. The objective of this study was to characterize systemic ghrelin levels after exercise with and without concomitant GH administration. 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. 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. 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.