Description
The ß-adrenergic receptors are linked to G proteins. The ß-receptor has three known subtypes. Beta-1 receptors primarily regulate myocardial tissue and affect the rate of contraction via impulse conduction. Beta-2 receptors regulate smooth muscle tone and influence vascular and bronchiolar relaxation. Beta-3 receptors are less well studied but are thought to primarily affect lypolysis and may have effects on cardiac inotropy (Greene Shepherd，2006). In the human heart, beta (1)- and beta (2)AR are the most powerful physiologic mechanism to acutely increase cardiac performance. Changes in betaAR play an important role in chronic heart failure (CHF). Thus, due to increased sympathetic activity in CHF, betaAR are chronically (over) stimulated, and that results in beta (1) AR desensitization and alterations of down-stream mechanisms (Brodde OE，2006).