Distinct role of adrenoceptor subtypes in cardiac adaptation to chronic pressure overload

1. With the generation of gene knockout (KO) or transgenic overexpression (TG) mouse models targeting adrenoceptors (AR), recent studies in vivo have investigated the role of AR subtypes in pressure overload-induced left ventricular (LV) hypertrophy and remodelling. 2. Although subjecting alpha(1B)-KO mice to transverse aortic constriction (TAC) did not reveal significant phenotype differences compared with controls, mice deficient in both alpha(1A)- and alpha(1B)-AR responded to TAC with poor survival, increased cardiomyocyte apoptosis, more severe fibrosis and dysfunction, but a similar degree of LV hypertrophy, compared with wild-type littermates. Following TAC, alpha(1B)-TG mice developed more severe hypertrophy, interstitial fibrosis and LV dysfunction. In contrast, overexpression of alpha(1A)-AR preserved cardiac function and reduced death from heart failure without affecting the degree of LV hypertrophy. Thus, alpha(1A)- and alpha(1B)-adrenoceptor signalling impacts differently on myocardial adaptation to pressure overload. 3. The absence of both beta(1)- and beta(2)-AR significantly suppressed pressure overload-evoked hypertrophy, fibrosis and expression of inflammatory or fibrogenic genes. Conversely, studies on beta(2)-TG mice with TAC revealed adverse consequences, including accelerated development of heart failure, poor survival and more severe interstitial fibrosis, but a comparable degree of hypertrophy compared with wild-type littermates. 4. Collectively, these findings suggest that the effect of ARs on pressure overload-induced myocardial adaptation is subtype specific. Whereas activation of alpha(1B)-AR or beta(2)-AR contributes to maladaptation and the onset of heart failure, activation of alpha(1A)-AR or inactivation of beta(2)-AR is beneficial in the setting of chronic pressure overload.