ABSTRACT
In porcine coronary arteries (PCAs), celiprolol, a selective ß(1)-adrenoceptors antagonist, induces vasodilatation by an endothelium- and nitric oxide (NO)-dependent pathway. However, the mechanisms of that vascular effect have not been precisely established. ß(3)-Adrenoceptors have been shown to be involved in the relaxation per se of various vascular beds, including coronary vessels. Thus, we evaluated (i) the presence of ß(3)-adrenoceptors in the PCA and (ii) their role in celiprolol-induced vasodilatation. PCA rings were placed in organ baths and preconstricted with KCl. All experiments were performed in the presence of nadolol (a ß(1)/ß(2)-adrenoceptor antagonist). Cumulative concentration-response curves to SR 58611A and ICI 215001 (2 ß(3)-adrenoceptor agonists) and to celiprolol were constructed. We also used semiquantitative reverse transcription - polymerase chain reaction, which clearly showed the presence of ß(3)-adrenoceptor transcripts. SR 58611A, ICI 215001, and celiprolol induced concentration-dependent relaxations in PCA rings. SR 58611A-induced relaxation was almost abolished after removal of endothelium or pretreatment with L-NAME (a NO synthase inhibitor). The vasorelaxations induced by SR 58611A and celiprolol were inhibited in the presence of SR 59230A and L-748337 (2 selective ß(3)-adrenoceptor antagonists). We showed (i) that PCAs possess functional ß(3)-adrenoceptors mediating endothelium- and NO-dependent relaxation, and (ii) that celiprolol exerts a ß(3)-adrenoceptor agonistic activity in this vascular bed.
Subject(s)
Adrenergic beta-3 Receptor Agonists/pharmacology , Celiprolol/pharmacology , Coronary Vessels/drug effects , Receptors, Adrenergic, beta-3/drug effects , Vasodilation/drug effects , Vasodilator Agents/pharmacology , Adrenergic beta-3 Receptor Antagonists/pharmacology , Animals , Coronary Vessels/metabolism , Dose-Response Relationship, Drug , Endothelium, Vascular/drug effects , Endothelium, Vascular/metabolism , Enzyme Inhibitors/pharmacology , Nitric Oxide/metabolism , Nitric Oxide Synthase/antagonists & inhibitors , Nitric Oxide Synthase/metabolism , RNA, Messenger/metabolism , Receptors, Adrenergic, beta-3/genetics , Receptors, Adrenergic, beta-3/metabolism , SwineABSTRACT
Circulating autoantibodies directed against the 2nd extracellular loop (EL-2) of ß(1)-adrenoceptors (ß(1)-AABs) have been detected in the serum of patients with various cardiovascular pathologies. ß(1)-AABs induce agonistic, positive inotropic effects via ß(1)-adrenoceptors (ß(1)ARs). In the mammalian heart, ß(1)-AR can exist in 2 distinct activated configurations (the so-called high- and low-affinity states). The aim of the present study was to investigate whether the action of ß(1)-AAB is dependent on the affinity state of ß(1)AR in isolated ventricular cardiomyocytes of adult Wistar rats. Immunoglobulin G (IgG) containing ß(1)-AAB obtained from animals immunized with a peptide corresponding to the EL-2 of human ß(1)-AR, caused a dose-dependent increase in cell shortening. Isoproterenol-induced inotropy was significantly reduced in cardiomyocytes that had been preincubated with IgG containing ß(1)-AAB and in cardiomyocytes isolated from immunized rats. The negative effects of preincubation with IgG containing ß(1)-AAB on the response to isoproterenol was inhibited in the presence of bisoprolol. CGP 12177A and pindolol-induced inotropy was not affected by IgG preincubation or immunization. No detectable inotropic effect of cell shortening was obtained with IgG containing ß(1)-AAB in the presence of propranolol and 3-isobutyl-1-methylxanthine. The present study demonstrates that ß(1)-AABs have no agonist/antagonist-like effects upon low-affinity state ß(1)-ARs. This result indicates that ß(1)-AABs recognize and stabilize the high-affinity state, but are unable to stabilize and (or) induce the low-affinity state receptor.
