Desensitization and resensitization of β1- and putative β4-adrenoceptor mediated responses occur in parallel in a rat model of cardiac failure

Abstract

1. Cardiostimulant effects of the non-conventional partial agonist, CGP 12177A, are mediated by a receptor distinct from the β3-adrenoceptor and termed the putative β4-adrenoceptor. Using a rat model of cardiac failure, induced by myocardial infarction (MI), we compared the desensitization and resensitization of responses to CGP 12177A with those to isoprenaline and RO 363 in left (LA) and right atria (RA). We also examined the ability of β-adrenoceptor antagonists to block responses to CGP 12177A. 2. MI reduced the maximum inotropic response to isoprenaline by 48% (sham 4.1 ± 0.6 mN, n = 10; MI 2.1 ± 0.4 mN, n = 8, P < 0.02), RO 363 by 61% (sham 4.2 ± 0.5 mN, n = 10 MI 1.8 ± 0.3 mN, n = 8, ..