Objective To evaluate whether active immunization producing β1- or β3-antibodies (β1-ABs and β3-ABs) detected in sera of patients with dilated cardiomyopathies has deleterious effects on vascular reactivity in Lewis rat thoracic aorta (TA) and small mesenteric arteries (SMA). Design and method Lewis rats were immunized for 6months with peptidic sequences corresponding to the second extracellular loop of β1- and β3-adrenoceptors (ARs). During the immunization, systolic blood pressure (SBP) was monitored using the tail cuff method. The vascular reactivity of immunized rats was assessed by ex vivo studies on SMA and TA using various β-AR agonists, phenylephrine and KCl. Results The immunizations producing functional β1-ABs and β3-ABs did not affect the SBP. However, in TA from β1-AR-immunized rats, the relaxations mediated by dobutamine and salbutamol were significantly impaired in comparison with adjuvant rats whereas nebivolol-induced relaxation was not modified. Moreover, phenylephrine and KCl-mediated contractions were enhanced in these rats. In contrast, immunization with β3-AR peptide led to the increase of relaxations induced by dobutamine in TA but did not change those induced by salbutamol and nebivolol. Surprisingly, in SMA from both rats immunized with β1- or β3-peptides, relaxations induced by the various β-agonists were not changed whereas phenylephrine and KCl-mediated contractions were impaired. Conclusions Our study shows that β1- and β3-ABs can affect vascular reactivity. β1-ABs would have a pathogenic action whereas β3-ABs would have a beneficial effect on aorta reactivity. Array( [0] => public://js/js_NhB8QqEMkIRnGegV_fyHSoTNS4QcuYAxmtYDZC610gE.js.gz : fichier présent sur le disque mais absent dans la base de données [1] => public://js/js_YqvqIXMHR_JA_6L7V5VgwgrhCDVtmWC_wCWsaINFQtk.js : fichier présent sur le disque mais absent dans la base de données [2] => public://js/js_YqvqIXMHR_JA_6L7V5VgwgrhCDVtmWC_wCWsaINFQtk.js.gz : fichier présent sur le disque mais absent dans la base de données [3] => public://js/js_NhB8QqEMkIRnGegV_fyHSoTNS4QcuYAxmtYDZC610gE.js : fichier présent sur le disque mais absent dans la base de données)