Distribution of myocardial beta-adrenoceptor subtypes and coupling to the adenylate cyclase in children with congenital heart disease and implications for treatment.

In congestive heart failure, down-regulation of myocardial beta-adrenoceptors (beta-AR) due to an elevated sympathetic tone is well known. In infancy and childhood, heart failure is usually related to congenital heart disease (CHD). Therefore, 71 samples of right atrial tissue of infants and children with CHD undergoing cardiac surgery were studied for beta-adrenoceptor density and distribution of the beta 1-/beta 2-AR subtypes. In 49 cases, the coupling of the beta-AR to the adenylate cyclase (AC) was examined. In a further study of 19 myocardial samples, AC was selectively stimulated with beta 1- or beta 2-AR whereas the other subtype was blocked by an antagonist. The following results were obtained: (1) Infants and children with severe acyanotic or cyanotic CHD had severely reduced beta-AR densities. (2) In most of the cases, the beta-AR down regulation is beta 1-subtype selective, but in critically ill newborns with congenital aortic valve stenosis or transposition of the great arteries, there is additional significant beta 2-AR down-regulation. In Fallot patients treated with the beta-antagonist propranolol, a significant increased beta-AR number compared with untreated Fallot patients was found. (3) beta-Adrenoceptor reduction in CHD is correlated with elevated noradrenaline plasma levels, thus proving a sympathetic dysregulation. (4) In CHD with moderate hemodynamic load, beta 2-AR coupling to AC was markedly more efficient than beta 1-AR coupling. The small number of myocardial beta 2-AR produced most of the cyclic adenosine monophosphate. (5) In severe acyanotic and cyanotic CHD, a partial decoupling of the beta 2-AR to the AC occurred.(ABSTRACT TRUNCATED AT 250 WORDS)