Tachykinin receptors mediating contraction of guinea pig lung strips

The aim of this study was to determine which tachykinin receptors mediate contraction in guinea pig lung parenchymal strips in vitro. Contraction caused by selective neurokinin-1 (NK-1), neurokinin-2 (NK-2), and neurokinin-3 (NK-3) receptor agonists and the natural agonists substance P (SP) and neurokinin A (NKA) was measured in the absence or presence of the NK-1 antagonist CP-96,345 and/or the NK-2 antagonist SR 48968. The NK-1 agonist [Sar9, Met(O2)11]-substance P and the NK-2 agonist [Nle10]-neurokinin A 4-10 caused similar concentration-dependent contractions that were inhibited by CP-96,345 and SR 48968, respectively. The NK-3 agonist [MePhe7]-neurokinin B also caused contraction, albeit at 10-fold higher concentrations, and this contraction was unaffected by either the NK-1 or NK-2 antagonist or the combination of both antagonists. Either CP-96,345 or SR 48968 alone had little effect on NKA-mediated contraction but administration of both antagonists virtually eliminated force generation. SP-induced tension was partially inhibited by SR 48968 and unaffected by CP-96,345. A second NK-1 receptor antagonist CP-99,994 also had no effect on SP-mediated tension. Therefore, NK-1, NK-2, and NK-3 agonists can all cause contraction in guinea pig lung strips, NKA-induced tension is mediated by both NK-1 and NK-2 receptors, and SP-induced contraction is mediated in part by NK-2 receptors. Both the SP and the [MePhe7]-neurokinin B data suggest that activation of a third neurokinin receptor subtype that is unaffected by an NK-1 receptor antagonist or an NK-2 receptor antagonist can cause contraction in guinea pig lung strips.