Erythropoietin Inhibits Basal and Stimulated Corticotropin-Releasing Hormone Release from the Rat Hypothalamus via a Nontranscriptional Mechanism

Abstract

Brain hypoxia-ischemia induces a local increase in the levels of erythropoietin (EPO) and vascular endothelial growth factor (VEGF); this condition is also associated with acute activation of the hypothalamo-pituitary-adrenal (HPA) axis, suggesting that increased levels of EPO and VEGF in the hypothalamus may play a role in the control of HPA function. Thus, in this study we used rat hypothalamic explants to investigate whether EPO and VEGF can directly modulate CRH release; the latter was assessed by RIA measurement of the peptide in the incubation medium and hypothalamic tissue. EPO and VEGF effects were studied in short-term (1-3 h) experiments under basal conditions or after stimulation with 56 mM KCl or 10 microM veratridine. We observed that EPO (1-10 nm) significantly reduced CRH release and, in parallel, increased intrahypothalamic CRH content. VEGF tended to reduce CRH release without reaching statistical significance. Moreover, EPO, but not VEGF, inhibited KCl- and veratridine-stimulated CRH release and counteracted the parallel decrease in intrahypothalamic CRH induced by the two secretagogues. EPO effects were not mediated by modification of CRH gene expression, either in the absence or the presence of KCl or veratridine; in this paradigm, KCl and veratridine per se did not modify CRH gene expression. Our findings suggest that EPO contributes to the regulation of the HPA axis activation; in pathological conditions such as brain ischemia, this growth factor may control the HPA axis function, preventing possible detrimental effects of HPA overactivation.