Heart ventricles specific stress-induced changes in β-adrenoceptors and muscarinic receptors

The left and right ventricles fulfill different role in heart function. Here we compare chamber specific changes in local catecholamine concentrations; gene expression and the receptor protein amount of all three beta-adrenoceptors (beta-AR) in rat right heart ventricles exposed to acute (1 session) and repeated (7 sessions) immobilization stress (IMMO) vs. previously observed changes in left ventricles. Density of muscarinic receptors as main cardio-inhibitive receptors was also measured. In the right ventricles, noradrenaline and adrenaline were increased. No beta(1)-AR changes were observed, in spite of the increased sympathetic activity. On the other hand, we have found a decrease of beta(2)-AR gene expression (reduction to 30%) after 7 IMMO and protein (to 59%) after 1 IMMO. beta(3)-AR gene expression was increased after 7 IMMO. Muscarinic receptor density was not changed. When comparing correlation in left and right ventricles, there was strong correlation between adrenaline and beta(2)-AR gene expression, protein and beta(3)-AR gene expression in the left ventricles while only correlation between adrenaline and beta(2)-AR mRNA and protein in the right ventricles was found. Our results show that maintenance of cardiac homeostasis under stress conditions are to a great extent achieved by a balance between different receptors and also by a balanced receptor changes in left vs. right ventricles. Taken together, decrease of cardio-stimulating beta(2)-AR represents a new important mechanism by which beta(2)-AR contributes to the heart physiology.