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In our study, we tried to determine the role of tachykinins (TKs) in the non-adrenergic non-cholinergic (NANC) nervous system responses obtained with electrical field stimulation (EFS) in isolated rat, guinea pig and mouse ileum. The Neurokinin1 (NK1) receptor antagonist, RP 67580, the Neurokinin 2 (NK2) receptor antagonist, GR 159897, and the Neurokinin 3 (NK3) receptor antagonist, SB 222200, were applied in the concentration range of 10-8-10-6M. RP 67580 partially decreased the contraction components of the NANC nervous system responses in the isolated rat, guinea pig and mouse ileums in a dose-dependent manner. While GR 159897 partially decreased the contraction components of the NANC nervous system responses in the isolated rat ileums in a dose-dependent manner, it was ineffective in isolated guinea-pig ileum. SB 222200 minimally reduced the contraction components of the NANC nervous system responses in the isolated rat ileum at 10-6M. It was ineffective on the contraction components of the isolated guinea pig and mouse ileums. As a conclusion, in our study while NK1 receptors are effective in 3 animal species, NK2 receptors are only effective in rats and NK3 receptors are ineffective in all 3 animal species for the contraction components of the NANC responses which are obtained with EFS in isolated rat, guinea-pig and mouse ileums. The possible reasons for the TK antagonists to have different effects in different animal species may be the difference between animal species, TK receptors' being localized in different places of ileum, species-dependent differences in receptor affinity between antagonists and different antagonists' being effective on different sub-types of NK1 and NK2 receptors.
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