Which adrenergic receptors are classified under the alpha category?

The classification of adrenergic receptors is fundamental to understanding their functions in the sympathetic nervous system. Alpha adrenergic receptors are divided into two main subtypes: Alpha 1 and Alpha 2.

Alpha 1 receptors are primarily responsible for mediating vasoconstriction, increased peripheral resistance, and other actions that elevate blood pressure. They achieve this by activating a Gq protein, which results in the activation of phospholipase C, leading to increased levels of inositol trisphosphate and diacylglycerol. This in turn causes an increase in intracellular calcium and smooth muscle contraction.

Alpha 2 receptors, on the other hand, act primarily as inhibitory receptors that can reduce neurotransmitter release in both the central and peripheral nervous systems. They are linked to Gi proteins, which inhibit adenylate cyclase, decreasing cAMP levels and leading to various downstream effects, including decreased sympathetic outflow.

The presence of both Alpha 1 and Alpha 2 receptors under the alpha category integrates their distinct but complementary roles within the adrenergic system. Recognizing this classification is essential for understanding how these receptors mediate physiological responses, such as blood pressure regulation and sedation during sympathetic activation.