CHAPTER 34 – Adrenergic Receptors in the Cardiovascular System

This chapter focuses on adrenergic receptors, which mediate important cardiovascular effects, including regulation of blood pressure, myocardial contractile rate (chronotropy), myocardial force (inotropy), and myocardial relaxation (lusitropism). The nine individual subtypes of ARs belong to three distinct receptor families: α1, α2, and β ARs. Each receptor has its own unique structural, biochemical, pharmacolgical, and physiological properties. In the cardiovascular system, α1-ARs are an important regulator of vascular tone and hence, blood pressure. They may also have effects on atrial conduction and play a role in the development of cardiac arrythmias. Hormone or agonist binding to members of the three families of adrenergic receptor α1, α2, and β initiates a cascade of molecular events, which includes coupling of the receptor with a heterotrimeric guanine nucleotide regulatory protein (G-protein) and subsequent interaction of the G-protein with various effector molecules. This signaling pathway is itself regulated dynamically, resulting in a dampening of agonist responses over time, a process referred to as desensitization. A family of G-protein receptor kinases plays an important role in uncoupling the receptor from the G-protein, resulting in desensitization.