Tachykinins: A family of biologically active peptides sharing a common conserved C-terminal sequence, -Phe-X-Gly-Leu-Met-NH2, where X is either an aromatic or a branched aliphatic amino acid. Members of this family have been found in mammals, amphibians, and mollusks. Tachykinins have diverse pharmacological actions in the central nervous system and the cardiovascular, genitourinary, respiratory, and gastrointestinal systems, as well as in glandular tissues. This diversity of activity is due to the existence of three or more subtypes of tachykinin receptors.Receptors, Tachykinin: Cell surface proteins that bind TACHYKININS with high affinity and trigger intracellular changes influencing the behavior of cells. Three classes of tachykinin receptors have been characterized, the NK-1; NK-2; and NK-3; which prefer, respectively, SUBSTANCE P; NEUROKININ A; and NEUROKININ B.Neurokinin A: 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.Receptors, Neurokinin-2: A class of cell surface receptors for tachykinins that prefers neurokinin A; (NKA, substance K, neurokinin alpha, neuromedin L), neuropeptide K; (NPK); or neuropeptide gamma over other tachykinins. Neurokinin-2 (NK-2) receptors have been cloned and are similar to other G-protein coupled receptors.Physalaemin: An oligopeptide isolated from the skin of Physalaemus fuscumaculatus, a South American frog. It is a typical kinin, resembling SUBSTANCE P in structure and action and has been proposed as a sialagogue, antihypertensive, and vasodilator.Neurokinin B: 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 A with the ability to excite neurons, dilate blood vessels, and contract smooth muscles, such as those in the URINARY BLADDER and UTERUS.Substance P: An eleven-amino acid neurotransmitter that appears in both the central and peripheral nervous systems. It is involved in transmission of PAIN, causes rapid contractions of the gastrointestinal smooth muscle, and modulates inflammatory and immune responses.Receptors, Neurokinin-3: A class of cell surface receptors for tachykinins that prefers neurokinin B (neurokinin beta, neuromedin K) over other tachykinins. Neurokinin-3 (NK-3) receptors have been cloned and are members of the G-protein coupled receptor superfamily. They have been found in the central nervous system and in peripheral tissues.Eledoisin: A peptide extracted from the posterior salivary glands of certain small octopi (Eledone spp., Mollusca), or obtained by synthesis. Its actions resemble those of SUBSTANCE P; it is a potent vasodilator and increases capillary permeability. (From Martindale, The Extra Pharmacopoeia, 30th ed, p1364)Neurokinin-1 Receptor Antagonists: Compounds that inhibit or block the activity of NEUROKININ-1 RECEPTORS.Receptors, Neurokinin-1: A class of cell surface receptors for TACHYKININS with a preference for SUBSTANCE P. Neurokinin-1 (NK-1) receptors have been cloned and are members of the G protein coupled receptor superfamily. They are found on many cell types including central and peripheral neurons, smooth muscle cells, acinar cells, endothelial cells, fibroblasts, and immune cells.QuinuclidinesKassinin: Dodecapeptide tachykinin found in the central nervous system of the amphibian Kassina senegalensis. It is similar in structure and action to other tachykinins, but is especially effective in contracting smooth muscle tissue and stimulating the micturition reflex.Receptors, Neurotransmitter: Cell surface receptors that bind signalling molecules released by neurons and convert these signals into intracellular changes influencing the behavior of cells. Neurotransmitter is used here in its most general sense, including not only messengers that act to regulate ion channels, but also those which act on second messenger systems and those which may act at a distance from their release sites. Included are receptors for neuromodulators, neuroregulators, neuromediators, and neurohumors, whether or not located at synapses.Capsaicin: An alkylamide found in CAPSICUM that acts at TRPV CATION CHANNELS.Guinea Pigs: A common name used for the genus Cavia. The most common species is Cavia porcellus which is the domesticated guinea pig used for pets and biomedical research.Eliminative Behavior, Animal: Behavior associated with the elimination of feces and urine from the body.Isoindoles: Benzopyrroles with the nitrogen at the number two carbon, in contrast to INDOLES which have the nitrogen adjacent to the six-membered ring.Piperidines: A family of hexahydropyridines.Thiorphan: A potent inhibitor of membrane metalloendopeptidase (ENKEPHALINASE). Thiorphan potentiates morphine-induced ANALGESIA and attenuates naloxone-precipitated withdrawal symptoms.Kinins: A generic term used to describe a group of polypeptides with related chemical structures and pharmacological properties that are widely distributed in nature. These peptides are AUTACOIDS that act locally to produce pain, vasodilatation, increased vascular permeability, and the synthesis of prostaglandins. Thus, they comprise a subset of the large number of mediators that contribute to the inflammatory response. (From Goodman and Gilman's The Pharmacologic Basis of Therapeutics, 8th ed, p588)Trachea: The cartilaginous and membranous tube descending from the larynx and branching into the right and left main bronchi.Neprilysin: Enzyme that is a major constituent of kidney brush-border membranes and is also present to a lesser degree in the brain and other tissues. It preferentially catalyzes cleavage at the amino group of hydrophobic residues of the B-chain of insulin as well as opioid peptides and other biologically active peptides. The enzyme is inhibited primarily by EDTA, phosphoramidon, and thiorphan and is reactivated by zinc. Neprilysin is identical to common acute lymphoblastic leukemia antigen (CALLA Antigen), an important marker in the diagnosis of human acute lymphocytic leukemia. There is no relationship with CALLA PLANT.Neuropeptides: Peptides released by NEURONS as intercellular messengers. Many neuropeptides are also hormones released by non-neuronal cells.Peptides, Cyclic: Peptides whose amino and carboxy ends are linked together with a peptide bond forming a circular chain. Some of them are ANTI-INFECTIVE AGENTS. Some of them are biosynthesized non-ribosomally (PEPTIDE BIOSYNTHESIS, NON-RIBOSOMAL).Muscle Contraction: A process leading to shortening and/or development of tension in muscle tissue. Muscle contraction occurs by a sliding filament mechanism whereby actin filaments slide inward among the myosin filaments.Benzamides: BENZOIC ACID amides.Pyrrolidonecarboxylic Acid: A cyclized derivative of L-GLUTAMIC ACID. Elevated blood levels may be associated with problems of GLUTAMINE or GLUTATHIONE metabolism.Atropine: An alkaloid, originally from Atropa belladonna, but found in other plants, mainly SOLANACEAE. Hyoscyamine is the 3(S)-endo isomer of atropine.Bronchoconstriction: Narrowing of the caliber of the BRONCHI, physiologically or as a result of pharmacological intervention.Muscle, Smooth: Unstriated and unstriped muscle, one of the muscles of the internal organs, blood vessels, hair follicles, etc. Contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei. Smooth muscle fibers are bound together into sheets or bundles by reticular fibers and frequently elastic nets are also abundant. (From Stedman, 25th ed)Calcitonin Gene-Related Peptide: Calcitonin gene-related peptide. A 37-amino acid peptide derived from the calcitonin gene. It occurs as a result of alternative processing of mRNA from the calcitonin gene. The neuropeptide is widely distributed in neural tissue of the brain, gut, perivascular nerves, and other tissue. The peptide produces multiple biological effects and has both circulatory and neurotransmitter modes of action. In particular, it is a potent endogenous vasodilator.Peptide Fragments: Partial proteins formed by partial hydrolysis of complete proteins or generated through PROTEIN ENGINEERING techniques.Evans Blue: An azo dye used in blood volume and cardiac output measurement by the dye dilution method. It is very soluble, strongly bound to plasma albumin, and disappears very slowly.Ileum: The distal and narrowest portion of the SMALL INTESTINE, between the JEJUNUM and the ILEOCECAL VALVE of the LARGE INTESTINE.