title: Chronic peripheral ouabain treatment affects the brain endothelin system of rats.
abstract: BACKGROUND
  Chronically administered ouabain increases the content of ouabain in several brain areas that are closely related to central cardiovascular regulation. However, the pattern of central changes induced by chronic infusion of ouabain is not completely understood.
  
  
  OBJECTIVE
  To investigate whether chronic peripheral ouabain treatment affects the brain endothelin system.
  
  
  METHODS
  By enzyme immunoassay, reverse transcription-polymerase chain reaction and autoradiography, we assessed brain endothelin and endothelin receptors contents following chronic (4 weeks) subcutaneous treatment of normotensive Sprague-Dawley rats with ouabain (OUA) (14 microg/kg per day). We also investigated the involvement of central endothelin receptors in increased sympathetic activity and hypertension induced by chronic OUA. Sympathetic activity was indirectly evaluated by recording changes in renal vascular resistance (RVR).
  
  
  RESULTS
  Brains of Sprague-Dawley rats collected following OUA treatment showed increased levels of the endothelin-1, and a decrease in ET(A) receptor mRNA and receptor levels. These, following chronic treatment with the submaximal dose of 14 microg/kg per day OUA, were a three-fold augmentation (P < 0.05) of the endothelin-1 peptide and a 38% decrease in ET(A) receptor mRNA. In addition, dose-dependent increases in RVR and in the basal mean arterial blood pressure (MABP) were found when compared with the vehicle (saline)-treated blood pressure (i.e. RVR, 14 microg/kg per day OUA, +161 +/- 15%). Total renal blood flows were consequently decreased (14 microg/kg per day OUA, P < 0.01). Interestingly, increases in RVR and MABP elicited by the submaximal dose of 14 microg/kg per day chronic OUA were significantly (P < 0.01) reduced by intra-periaqueductal gray (PAG) microinjections of FR139317 (selective ET(A) receptor antagonist, 5 nmol) and SB209670 (ET(A)/ET(B) non-selective antagonist, 3 nmol), but not by BQ 788 (selective ET(B) receptor antagonist, 5 nmol).
  
  
  CONCLUSIONS
  These data indicate that chronic treatment with OUA increases central endogenous synthesis/release of endothelin. This contributes to the peripheral OUA actions. As an example, an antagonism at the PAG endothelin receptors, mainly of the ET(A) type, reduced the effects of chronic OUA on both MABP and RVR.
authors.affiliation: Department of Experimental Medicine, Section of Pharmacology 'Leonardo Donatelli', Research Centre for Cardiovascular Diseases, Faculty of Medicine and Surgery, 2nd University of Naples, Italy.
authors.forename: Clara
authors.initials: C
authors.lastname: Di Filippo
authors.forename: Amelia
authors.initials: A
authors.lastname: Filippelli
authors.forename: Barbara
authors.initials: B
authors.lastname: Rinaldi
authors.forename: Elena
authors.initials: E
authors.lastname: Piegari
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Esposito
authors.forename: Francesco
authors.initials: F
authors.lastname: Rossi
authors.forename: Michele
authors.initials: M
authors.lastname: D'Amico
mesh_terms: D000818:Animals; D001345:Autoradiography; D001381:Azepines / Q000378:metabolism / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D002316:Cardiotonic Agents / Q000494:pharmacology*; D065130:Endothelin A Receptor Antagonists; D019332:Endothelin-1 / Q000378:metabolism*; D007211:Indoles / Q000494:pharmacology; D008297:Male; D009842:Oligopeptides / Q000378:metabolism / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology*; D010487:Periaqueductal Gray / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044022:Receptor, Endothelin A / Q000235:genetics / Q000378:metabolism; D012077:Renal Artery / Q000502:physiology; D014655:Vascular Resistance / Q000187:drug effects
chemical_list: D001381:Azepines; D002316:Cardiotonic Agents; D065130:Endothelin A Receptor Antagonists; D019332:Endothelin-1; D007211:Indoles; D009842:Oligopeptides; D044022:Receptor, Endothelin A; C079574:FR 139317; C087850:PD 151242; D010042:Ouabain