beta-adrenoceptor

Beta-adrenoceptors are the other main family that responds to adrenaline and norepinephrine. As a rough rule of thumb, they tell the heart to work harder and tell smooth muscle in the airways and elsewhere to relax, which is almost the opposite of what alpha receptors do to vessels.

All beta receptors are G-protein-coupled receptors that couple to Gs and raise cyclic AMP inside the cell. Beta-1 receptors dominate in the heart, increasing rate and force; beta-2 receptors relax bronchial and vascular smooth muscle and the uterus; beta-3 receptors act on fat tissue and the bladder. A simple memory aid is that you have one heart (beta-1) and two lungs (beta-2).

These receptors anchor two enormous drug groups. Beta-2 agonists are the mainstay of asthma relievers, while beta blockers (beta antagonists) slow and protect the heart in angina, hypertension, arrhythmias, and heart failure. Selectivity matters: a beta-1-selective blocker is safer in a patient who also has asthma.