Growth Hormone And Cortisol Alterations After Inhibition/stimulation Of Hpa Axis In Healthy Adults.

Abstract

PURPOSE: To examine serum growth hormone (GH) and cortisol (COR) responses to a selected aerobic exercise protocol performed under inhibition or stimulation of the HPA axis in healthy male and female volunteers. METHODS: Twelve healthy volunteers (8 males, 4 females, age: 30.6 ± 4.4 yrs, body mass: 77.3 ± 12.3 kg, height: 1.77 ± 0.07 m), performed a single bout of 30 min aerobic exercise at 70%VO2 max on a treadmill, on three different conditions [control (C), HPA axis inhibition (HPA-I, induced by glucocorticoid administration), HPA axis stimulation (HPA-S, induced by ACTH administration)], following standard diet. Blood samples were collected before (t0), at the end of the exercise bout (t30), and 30 min later (t60) and serum GH and COR were measured. Two-way ANOVA was used for statistics. Data is presented as mean ± SE. RESULTS: In C condition, GH significantly increased (p < 0.001) after exercise and decreased again 30 min after exercise without reaching pre-exercise levels (0.2 ± 0.1; 5.5 ± 1.1; 1.7 ± 0.7 ng/mL; at t0, t30 and t60, respectively). COR significantly decreased 30 min after exercise (p < 0.005) (13.9 ± 1.2; 10.3 ± 1.1; 7.1 ± 1.2 μg/dL; at t0, t30 and t60, respectively). In HPA-I, GH significantly increased at the end of exercise (p < 0.05) while 30 min after exercise it decreased reaching pre-exercise levels (1.1 ± 0.3; 3.0 ± 0.6; 1.0 ± 0.2 ng/mL; at t0, t30 and t60, respectively). COR remained unchanged (p > 0.05) (0.627 ± 0.1; 0.632 ± 0.1; 0.639 ± 0.1 μg/dL; at t0, t30 and t60, respectively). Under HPA-S condition, GH significantly increased 30 min after exercise (p < 0.001) (0.3 ± 0.1; 8.9 ± 1.9; 3.1 ± 0.9 ng/mL; at t0, t30 and t60, respectively. COR significantly increased after exercise (p < 0.001) (14.7 ± 1.1; 30.7 ± 1.3; 34.6 ± 3.7 μg/dL; at t0, t30 and t60, respectively). There were no significant changes in COR between the three conditions, while COR was lower in HPA-I compared to C condition at all time points (p < 0.001). There were no significant differences between male and female participants. CONCLUSIONS: The rapid increase of GH in response to aerobic exercise is not affected by the modification of HPA axis. The specific aerobic exercise regimen influenced circulating COR yet not under exogenous inhibition of the HPA axis. Further studies will characterize how those responses are regulated by the characteristics of exercise.