What receptors and receptor subtypes mediate sympathetic nervous system effects on the heart and vasculature?

• A. Adrenergic receptors; alpha1/alpha2 and beta1/beta2 (beta3); heart effects mainly via beta1; vascular tone via alpha1
• B. Cholinergic muscarinic receptors
• C. Dopaminergic receptors
• D. Serotonergic receptors

Answer: (A)

Sympathetic effects on the heart and vessels are produced by adrenergic receptors. The heart mainly responds through beta1 receptors, so their activation increases heart rate, contractility, and conduction velocity via higher cAMP and calcium availability. In the vasculature, alpha1 receptors on vascular smooth muscle cause vasoconstriction, raising vascular resistance and blood pressure. Beta2 receptors can cause vasodilation in certain beds (like skeletal muscle), but overall vascular tone is dominated by alpha1 activity. The other receptor types listed don’t mediate these sympathetic cardiovascular actions: muscarinic receptors are part of parasympathetic signaling, while dopaminergic and serotonergic receptors are not the primary mediators here.