Substance P is an undecapeptide member of the tachykinin neuropeptide family mainly secreted by neurons and is involved in many biological processes, including nociception and inflammation. The endogenous receptor for substance P is neurokinin 1 receptor although it also activates neurokinin 2 and neurokinin 3. Substance P is involved in the axon reflex-mediated vasodilatation to local heating and wheal and flare reaction. It has been shown that vasodilatation to substance P is dependent on the NK1 receptor located on the endothelium. In contrast to other neuropeptides studied in human skin, substance P-induced vasodilatation has been found to decline during continuous infusion. Preclinical data support the notion that Substance P is an important element in pain perception. The sensory function of substance P is thought to be related to the transmission of pain information into the central nervous system. Substance P coexists with the excitatory neurotransmitter glutamate in primary afferents that respond to painful stimulation. Substance P and other sensory neuropeptides can be released from the peripheral terminals of sensory nerve fibers in the skin, muscle, and joints. It is proposed that this release is involved in neurogenic inflammation, which is a local inflammatory response to certain types of infection or injury. Substance P appears to have an important role in nausea and vomiting. In 2004, the NK1 antagonist aprepitant (brand name Emend) was approved by the U.S. FDA for the treatment of chemotherapy-induced nausea and vomiting

Bradykinin, a pro-inflammatory mediator is also a neuromediator and regulator of several vascular and renal functions. Bradykinin can act as a vasoactive substance along with histamine in inflammation and swelling as it is a potent vasodilator. In addition, it triggers the release of other mediators such as nitric oxide in inflammatory and cancer tissues. Bradykinin acts via specific cell surface receptors: bradykinin receptor, B1 and B2 that are G-protein coupled receptors of the seven-transmembrane domain family. It was shown that increased plasma levels of bradykinin lead to the angioedema as the common major clinical manifestation. Bradykinin was also studied in heart transplant recipients and in obesity patients, but these studies were terminated or withdrawn for different reasons. Bradykinin is also an important growth factor for many cancers. Bradykinin antagonists showed higher potency than standard anti-cancer drugs, without evident toxicity to the hosts, that is why they have great promise for the development of new anti-cancer drugs.