Substance P was found in the gut as well as in the brain. It is responsible for a number of excitatory effects on both central and peripheral neurons. Substance P contracts smooth muscle, constricts bronchioles and increases capillary permeability. When released from afferent nerves, Substance P causes a neurogenic inflammatory response, including mast cell degranulation. NK-1 agonist; potent vasodilator and hypotensive agent; induces salivation; putative neurotransmitter in sensory (pain) afferents. [Nle11]-Substance P is a Substance P analog that avoids methionine oxidation problems.