Reductions in plasma prolactin during acute erythropoietin administration.

OBJECTIVES The presence of erythropoietin (EPO) and its receptors in several central nervous system regions indicates additional functions beside its hematopoietic role. Preclinical data suggest that it may slow down the process of neuronal loss, and that EPO may cause dopamine release, and thus influence hormone release, especially prolactin. This possibility has not yet been studied in humans. METHODS During a clinical trial on possible protective effects in patients with amyotrophic lateral sclerosis (ALS), we studied the acute effects of EPO administration on prolactin, the release of which is under tonic inhibition of hypothalamic-pituitary dopaminergic activity. Prolactin as well as EPO levels were estimated in blood samples taken every 30 min over 2 hours after administration of 3000 IU EPO i.v. in seven male and four female patients with ALS. RESULTS The baseline PRL levels of the 11 patients were all within normal range (4.5-10.5 ng/ml). EPO administration caused a significant reduction in prolactin levels, maximal at 60 min after administration. Reductions in PRL were not related to EPO dose (IU per kg body weight), or to duration of illness. CONCLUSIONS The findings indicate that EPO promotes dopamine release in humans, and is consistent with preclinical data showing that EPO releases dopamine from rat striatal slices. Previous reports showed that dopaminergic neurons express EPO receptors, which exert a facilitating action on dopamine release, and the present data indicate that this may hold true in humans.