Increased prolactin response to hyperoxia at rest and during endurance exercise.

Neuroendocrine responses were investigated in 8 male athletes before, during and after 60 min of bicycle ergometry at an intensity corresponding to 1.5 mmol/l blood lactate in an incremental bicycle test. Hyperoxic gas (HE: 100% O2), hypoxic gas (HO: 14% O2, 86% N2) or normoxic gas (NO) were inhaled continuously during exercise as well as for 30 min before and after. During exercise, prolactin (PRL) increased in HO while it did not change significantly in NO. Only HE induced a PRL increase (400%) during 30 min of rest before exercise. PRL decreased in HE during exercise but remained higher than in HO. Growth hormone (GH), ACTH and norepinephrine (NE) did not increase in a similar pattern during HE. In comparison to NO and HE, increase of NE, GH and ACTH was significantly higher in HO, NE declined significantly in HE before exercise. Our results demonstrate that only PRL is affected by acute exposure to hyperoxia. Changes in inhibition of the dopaminergic system might contribute to augmentation of PRL before exercise. The exact underlying mechanisms are yet unknown.