Characterisation of the Neurokinin Receptors Mediating Contraction of Isolated Tracheal Preparations from a Variety of Species

Abstract

The effects of neurokinin (NK) agonists on isolated tracheal preparations from rat (RT), pig (PT), rabbit (RbT) and guinea-pig (GPT) have been investigated. None of the NKs contracted RT, suggesting that this preparation lacks NK receptors mediating contraction, whereas NKs caused concentration- related contractions of PT, RbT and GPT. In PT, NK1-receptors mediate contraction since only substance P (SP) and the NK1-receptor selective agonists, SP methylester (SPOMe) and GR73632 were highly potent. In contrast, in RbT, only NKA and the selective NK2-receptor agonist, GR64349 were potent, indicating the presence of NK2-receptors. However, in GPT both NK1- and NK2-receptors appear to mediate contraction to NKs since NKA, GR73632 and GR64349 were highly potent and SP and SPOMe moderately potent agonists. This study demonstrates apparent species differences in the NK-receptor populations present in tracheal smooth muscle.