Beta-adrenergic signalling

Noradrenaline and adrenaline stimulate beta receptors. Beta-1 receptors, concentrated in cardiac tissue, raise cAMP and increase heart rate, conduction velocity, and contractility, and stimulate renin release. Beta-2 receptors, concentrated in airway and vascular smooth muscle, raise cAMP and relax the muscle, dilating airways. Beta blockers antagonize beta-1 (selectively or not): rate, conduction, contractility, and renin all fall. Beta-2 agonists like salbutamol activate airway beta-2: bronchodilation. Selectivity is relative on both sides. Cardioselective blockers reach beta-2 at higher doses (bronchospasm risk in asthma), and beta-2 agonists reach beta-1 at higher doses (tremor, tachycardia).