Penbutolol

Penbutolol is a non-selective β-blocker. The β₁, β₂, and β₃ receptors are all Gs protein-coupled receptors. Once activated, they stimulate adenylyl cyclase, increase cAMP concentration, and subsequently activate protein kinase A, leading to downstream cellular responses. Penbutolol blocks β₁ receptors on cardiomyocytes, suppressing Gs-cAMP signaling, reducing myocardial contractility, and thereby lowering cardiac output and blood pressure. In addition, Penbutolol also blocks β₂ receptors on peripheral blood vessels and bronchial smooth muscle, lowering cAMP levels and weakening smooth muscle relaxation, which may cause bronchoconstriction and increased peripheral vascular resistance.