Final answer:
Norepinephrine stimulates its own release by agonizing alpha-2 receptors (option c) , which are involved in a negative feedback mechanism that controls neurotransmitter release.
Step-by-step explanation:
The question pertains to the self-stimulation of norepinephrine (NE) release through adrenergic receptors. Norepinephrine can stimulate its own release by agonizing alpha-2 receptors. These receptors, when activated, can inhibit the further release of NE; however, in the context of the autoregulation of NE release, the alpha-2 receptor acts in a feedback mechanism to control the release of NE. This is in contrast to alpha-1, beta-1, and beta-2 receptors, which have different roles in the body's response to catecholamines.
The mechanism by which the alpha-2 receptor works involves coupling to Gi proteins, which results in a decrease of cAMP activity within the cell, ultimately leading to cellular effects such as smooth muscle contraction. The alpha-2 adrenergic receptor has three subtypes - α2A, α2B, and α2C - each with specific actions in different tissues, including the inhibition of insulin release in the pancreas.