title: Erythropoietin potentiates EDHF-mediated dilations in rat middle cerebral arteries.
abstract: The neuroprotective effects of exogenous erythropoietin (EPO) in animals and humans after brain injury may be afforded, in part, by the influence of EPO on cerebral arteries. We tested (1) if EPO itself is vasoactive and (2) if EPO enhances endothelium-mediated dilations, specifically those mediated by endothelium-derived hyperpolarizing factor (EDHF). Immunoblotting and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to detect EPO receptor. Rat middle cerebral arteries (MCAs) were isolated, pressurized, and perfused in vitro. EPO was directly applied to MCAs to test its vasoactivity. Endothelium-mediated dilations were elicited by UTP, whereas EDHF-mediated dilations were elicited by UTP after inhibition of endothelial nitric oxide synthase and cyclooxygenase. mRNA and protein for EPO receptor was found in rat MCA. Abluminal application of 0.001-10 U/mL EPO, which is selective for vascular smooth muscle, did not alter vessel diameter. In contrast, luminal application of EPO, which is selective for endothelium, resulted in concentration-dependent dilations of up to 39 +/- 16% at 10 U/mL (p = 0.0018), though responses were variable. A single dose of EPO (1,000 U/kg) administered to rats 24 h prior to examining vascular function potentiated dilations to UTP 2.6-fold (p < 0.0001). EDHF-mediated dilations were potentiated 2.1-fold following in vivo EPO treatment (p = 0.0034). This study demonstrates that EPO can directly dilate rat MCAs via the endothelium, though not all vessels are responsive. Additionally, pre-treatment with EPO for 24 h in vivo potentiates endothelium-mediated dilations, specifically those mediated by EDHF. Thus, enhanced endothelium-mediated dilations may partially underlie the neuroprotective effects of EPO after brain injury.
authors: Section of Pediatric Critical Care Medicine, Baylor College of Medicine, Houston, Texas, USA.
authors: Nadeem I
authors: NI
authors: Shafi
authors: Jon
authors: J
authors: Andresen
authors: Sean P
authors: SP
authors: Marrelli
authors: Robert M
authors: RM
authors: Bryan
mesh_terms: D000818:Animals; D001685:Biological Factors / Q000378:metabolism / Q000494:pharmacology*; D001930:Brain Injuries / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000187:drug effects* / Q000502:physiology; D019610:Cytoprotection / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D004921:Erythropoietin / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D020768:Middle Cerebral Artery / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D020318:Rats, Long-Evans; D017467:Receptors, Erythropoietin / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D016896:Treatment Outcome; D014544:Uridine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology; D014665:Vasodilator Agents / Q000378:metabolism / Q000494:pharmacology
chemical_list: D001685:Biological Factors; D017467:Receptors, Erythropoietin; D014665:Vasodilator Agents; C067410:endothelium-dependent hyperpolarization factor; D004921:Erythropoietin; D014544:Uridine Triphosphate