Kinetensin is a neurotensin-like peptide isolated from pepsin-treated human plasma. IC50 & Target: Neurotensin Receptor^[1] In Vitro: The peptide kinetensin isolated from pepsin-treated human plasma induces a dose-dependent release of histamine when exposed to rat peritoneal mast cells. The threshold concentration is around 1 μM, the ED₅₀ is 10 μM, and the optimal concentration of between 100 to 1000 μM released 80% of the total histamine. Kinetensin is 10 to 100 times less potent than neurotensin and equipotent with the opioid peptide dynorphin. The histamine release is clearly temperature-dependent, with no release occurring at 0 or 45 °C and with an optimum around 37 °C. The histamine release is significantly reduced in the absence of extracellular calcium^[2]. In Vivo: Kinetensin also induces a dose-dependent increase in vascular permeability when injected intradermally into rats^[2].