Proenkephalin-A is a secreted protein that belongs to the opioid neuropeptide precursor family. Proenkephalin-A is an endogenous opioid polypeptide hormone which, via proteolyic cleavage, produces the enkephalin peptides [Met]enkephalin, and to a lesser extent, [Leu]enkephalin. Met- and Leu-enkephalins compete with and mimic the effects of opiate drugs. They play a role in a number of physiologic functions, including pain perception and responses to stress. Proenkephalin-A (114-133) and Proenkephalin-A (237-258) increase glutamate release in the striatum. Proenkephalin-A (114-133) decreases GABA concentration in the striatum.