Adrenaline and noradrenaline increase contractile force of human ventricle through both beta 1- and beta...

Several paradoxical findings have come to light with regard to the function of beta 1- and beta 2-adrenoceptors that coexist in human ventricular myocardium. Although a predominance of beta 1 (greater than 2/3) was found in membrane particles, stimulation of the adenylate cyclase was mostly through beta 2 (5/6 adrenaline and 2/3 noradrenaline). One beta 2-adrenoceptor generates 4-12 times more cAMP.s-1 than one beta 1-adrenoceptor. Both adrenaline and noradrenaline can enhance maximally contractile strength through beta 1. Low adrenaline concentrations and high noradrenaline concentrations can increase contractile strength by up to 50% of maximum through beta 2. The question as to whether beta 1- or beta 2 augment contractile strength at a different oxygen cost still needs elucidation.