The effects of docosahexaenoic acid supplementation and exercise on growth hormone and insulin-like growth factor I serum levels during chronic hypoxia in rats

Abstract

In this study we examined the effects of docosahexaenoic acid (DHA) on growth hormone (GH), insulin-like growth factor I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) in response to chronic hypoxia and exercise training in hypoxic conditions. Thirty-five rats were divided into five groups; control group (C), hypoxia group (H), hypoxia-exercise group (HE), hypoxia-docosahexaenoic acid group (HD), hypoxia-exercise-docosahexaenoic acid group (HED). A treadmill exercise was performed as 30 m/min for 20 min/day, 5 days per week for 28 days at level grade for the exercising groups (HE and HED). DHA was given to the HD and HED groups every day orally (36 mg/kg). The animals, except for the C group, were exposed to hypoxia for 28 days. Serum levels of GH and IGF-I in the H group decreased after chronic hypoxia (p<0.001). GH and IGF-I in the HD group also decreased compared with the C group (p<0.05, p<0.01, respectively). GH in C group did not show significant difference compared with the HE and HED groups. Decreased serum level of IGF-I was observed for the HED group (p<0.05). According to our findings, chronic hypoxia exposure decreases serum levels of GH, and IGF-I and exercise training have a slightly positive effect on GH/IGF-I axis during hypoxia. In addition, DHA supplementation slightly increases GH and IGF-I serum levels in hypoxic conditions. However, this effect on GH/IGF-I axis during hypoxia is not strong compared with exercise. Therefore, we concluded that exercise and/or DHA supplementation does not have additional positive effect on these hormones in hypoxic conditions.