Nolpitantium Free Base is a highly selective nonpeptide antagonist of neurokinin-1 (NK1) receptor. Nolpitantium potently, selectively and competitively inhibited substance P binding to NK1 receptors from various animal species, including humans. In vitro, it was a potent antagonist in functional assays for NK1 receptors such as [Sar9, Met(O2)11]substance P-induced endothelium-dependent relaxation of rabbit pulmonary artery and contraction of guinea-pig ileum. Up to 1 mkM, Nolpitantium had no effect in bioassays for NK2 and NK3 receptors. The antagonism exerted by Nolpitantium toward NK1 receptors was apparently non-competitive, with pD2' values between 9.65 and 10.16 in the different assays. Nolpitantium also blocked in vitro [Sar9, Met(O2)11]substance P-induced release of acetylcholine from rat striatum. In vivo, Nolpitantium exerted highly potent antagonism toward [Sar9, Met(O2)11]substance P-induced hypotension in dogs, bronchoconstriction in guinea-pig) and plasma extrava......