Activity of spantide I and II at various tachykinin receptors and NK-2 tachykinin receptor subtypes.

We compared the ability of spantide I and II to antagonize tachykinins in monoreceptor bioassays. Both peptides antagonized the response to substance P methylester in the guinea-pig ileum (NK-1 receptor-mediated) with greater affinity than the responses mediated by NK-2 or NK-3 receptors in other bioassays. Spantide II was about 10 times more potent than spantide I as an NK-1 antagonist and also possessed some selectivity for the NK-2 receptor subtype present in the hamster trachea. Spantide II is a suitable tool to assess the role of NK-1 receptors in the central and peripheral nervous system.