Neurokinin A is a member of the tachykinin family of neuropeptide neurotransmitters. It is produced from the same preprotachykinin A gene as the neuropeptide substance P. It has various roles in the body of humans and other animals. One specific example is mediating contraction of the rat colon and bronchoconstriction through the non-adrenergic non-cholinergic nervous system . A mammalian neuropeptide of 10 amino acids that belongs to the tachykinin family. It is similar in structure and action to SUBSTANCE P and NEUROKININ B with the ability to excite neurons, dilate blood vessels, and contract smooth muscles, such as those in the BRONCHI.

Neuropeptide K (which has also been called neurokinin K)and neuropeptide gamma are N-terminally longer versions of neurokinin A, produced from the same splice forms of the same gene, which appear to be final peptide products in some tissues.