Cardiovascular Pharmacology Function of cardiac β 1 - and β 2 -adrenoceptors of newborn piglets: Role of phosphodiesterases PDE3 and PDE4 Alejandro Galindo-Tovar a , Maria Luisa Vargas a , Alberto J. Kaumann b, ⁎ a Department of Pharmacology, Medical School, University of Murcia, and Research Unit of the University Hospital Virgen de la Arrixaca, Murcia 30100, Spain b Department of Physiology, Development & Neuroscience, University of Cambridge, Downing Street, Physiology Building, Cambridge CB2 3EG, UK abstract article info Article history: Received 1 December 2009 Received in revised form 19 March 2010 Accepted 12 April 2010 Available online 18 April 2010 Keywords: Piglet heart β 1 -adrenoceptor β 2 -adrenoceptor Noradrenaline and adrenaline Sinoatrial tachycardia and contractile force cAMP (cyclic adenosine monophosphate) Phosphodiesterase3 Phosphodiesterase4 The structures of porcine and human β 2 -adrenoceptors differ but the repercussions for porcine cardiac function are unknown. We investigated the function of porcine β 2 -adrenoceptors in 3 cardiac regions, sinoatrial node, left atrium and right ventricle of newborn piglets. Both (-)-noradrenaline and (-)-adrenaline caused sinoatrial tachycardia: 60 ± 10% and 62 ± 7% of the maximum response (E max ) to (-)-noradrenaline (-logEC 50 = 9.0) and (-)-adrenaline (-logEC 50 = 7.5) respectively, were resistant to antagonism by the β 1 -selective CGP20712A (2-hydroxy-5-[2- [[2-hydroxy-3-[4-[1-methyl-4-(trifluoromethyl)-1H-imidazol-2-yl]phenoxy]propyl]amino]ethoxy]-benzamide) (300 nM) but antagonized by β 2 -selective ICI118551 (erythro(±)-[1-(2,3-dihydro-7-methyl-1H-inden-4-yl)oxy]- 3-[(1-methylethyl)amino]-2-butanol) (50 nM), consistent with mediation through β 2 -adrenoceptors. The phosphodiesterase3-selective inhibitor cilostamide and phosphodiesterase4-selective inhibitor rolipram did not affect catecholamine chronotropic potencies. Only small CGP20712A-resistant positive inotropic effects of (-)- adrenaline were detected in the left atria (13 ± 2% of E max ) and ventricular trabeculae (14 ± 5% of E max ). The atrial inotropic responses to (-)-noradrenaline and (-)-adrenaline faded; fades were prevented by rolipram but not cilostamide or concurrent cilostamide + rolipram respectively. (-)-Noradrenaline (ICI118551 present) increased left atrial cAMP levels through β 1 -adrenoceptors that were markedly enhanced by rolipram but unaffected by cilostamide. Concurrent cilostamide + rolipram uncovered inotropic and cAMP responses to (-)-adrenaline (CGP20712A present). We conclude that sinoatrial β 2 -adrenoceptors are more important than β 1 -adrenoceptors in the mediation of tachycardia caused by both (-)-noradrenaline and (-)-adrenaline in the newborn piglet. β 2 - adrenoceptors have only a minor role in the mediation of left atrial and ventricular inotropic effects of (-)- adrenaline. Catecholamine-evoked tachycardia is not controlled by PDE3 or PDE4. PDE4, but not PDE3, controls the atrial inotropic and cAMP β 1 -adrenoceptor-mediated responses to (-)-noradrenaline. Both PDE3 and PDE4 blunt left atrial inotropic and cAMP responses to (-)-adrenaline through β 2 -adrenoceptors. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The porcine heart has been used as a model for the study of human 5-HT 4 receptor function in different cardiac regions (Kaumann, 1990; Parker et al., 1995; Brattelid et al., 2004; Galindo-Tovar et al., 2009a). In contrast, although some biochemical information exists about β-adreno- ceptor subtypes in porcine heart, little is known, however, about the function of these receptors in different cardiac regions, particularly in the heart from newborn piglets. Receptor-binding studies in the right atrium from newborn piglet showed 89% β 1 - and 11% β 2 -adrenoceptors (Kaumann et al., 1995), consistent with mRNA detected for these receptors in porcine heart (McNeel and Mersmann, 1999). The lack of functional evidence about porcine cardiac β-adrenoceptor subtypes may in part be related to the structural differences between porcine and human β 2 -adrenoceptors (Liang et al., 1997)(Fig. 1). In particular, unlike other species, the affinity of the β 2 -selective antagonist ICI118551 for recombinant porcine β 2 -adrenoceptors appears to be notoriously low (Liang and Mills, 2001; Sillence et al., 2005), rendering difficult the analysis of these receptors in porcine tissues, including the heart. Cyclic AMP, generated through activation of cardiac Gs protein- coupled receptors, is mainly hydrolysed by phosphodiesterases (PDE) isoenzymes PDE3 and PDE4 (Fischmeister et al., 2006; Nikolaev et al., 2006; Houslay, 2009). We recently found that both PDE3 and PDE4 jointly reduce the 5-HT-evoked cAMP and inotropic signals through left atrial 5-HT 4 receptors of newborn piglets. In contrast, the (-)-isopren- aline-evoked cAMP signal is markedly reduced by PDE4, unaffected by PDE3 but it is unknown whether β 1 - and/or β 2 -adrenoceptors are involved (Galindo-Tovar et al., 2009a). To address this question we designed conditions of selective activation of β 1 - and β 2 -adrenoceptors by (-)-noradrenaline and (-)-adrenaline respectively. Since the function of coexisting β 1 - and β 2 -adrenoceptors in different cardiac regions of newborn piglet is virtually unknown, we first sought to investigate their relative importance in mediating catecholamine-evoked sinoatrial tachycardia and positive inotropic European Journal of Pharmacology 638 (2010) 99–107 ⁎ Corresponding author. Tel.: + 44 1223 333810; fax: + 44 1223 333840. E-mail address: ajk41@hermes.cam.ac.uk (A.J. Kaumann). 0014-2999/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ejphar.2010.04.013 Contents lists available at ScienceDirect European Journal of Pharmacology journal homepage: www.elsevier.com/locate/ejphar