A given adrenergic agent induces lipolysis, release of renin, and increases myocardial contractility. These effects are attributed to which receptor type?

• A. α1 Receptors
• B. α2 Receptors
• C. β1 Receptors
• D. β3 Receptors

Answer: (A)

β1-adrenergic receptors are responsible. They are Gs-coupled, so when activated they raise cAMP inside cells. In the heart, this boosts calcium influx and strengthens contraction. In juxtaglomerular cells of the kidney, higher cAMP promotes renin release. In adipocytes, cAMP activates hormone-sensitive lipase, driving lipolysis. While other receptor types can influence some of these processes (α1 mainly causes vasoconstriction, and β3 handles adipose lipolysis with less effect on heart and renin), none tie together all three effects as clearly as β1 receptors do.