Final answer:
The Adrenergic β2 receptors are activated by low concentrations of epinephrine and cause vasodilation by increasing intracellular cAMP, leading to smooth muscle relaxation.
Step-by-step explanation:
The autonomic receptor activated by low concentrations of epinephrine released from the adrenal medulla that causes vasodilation is the Adrenergic β2 receptors (Option C). Epinephrine is capable of acting on both α-adrenergic and β-adrenergic receptors. At lower concentrations, the effect on the β-adrenergic receptors is dominant, specifically the β2 subtype, resulting in vasodilation. The β2-adrenergic receptors are coupled to Gs proteins, which leads to an increase in intracellular cAMP activity. This action typically results in smooth muscle relaxation.
In comparison, α-adrenergic receptors, notably the α1 subtype, are more associated with vasoconstriction effects. High levels of epinephrine preferentially activate these receptors over β2 receptors, which leads to blood vessel constriction. It's important to note that the adrenergic receptors are part of a broader system of autonomic regulation involving cholinergic receptors as well, although they are not the focus in the context of this question.