抄録
We characterized the pharmacological nature of the tachykinin receptor subtype mediating the contractile response to electrical transmural stimulation (ETS) in the isolated rabbit iris sphincter muscle preparation by using selective NK1-receptor antagonists, spantide and L-668, 169, and a selective NK2-receptor antagonist, L-659, 877. ETS caused a biphasic contraction in this preparation: a rapidly developing cholinergic component followed by a slowly decaying tachykininergic component. The tachykininergic contractile response to ETS was effectively attenuated by spantide and L-668, 169, but only slightly by L-659, 877, indicating that the tachykinin receptors mediating ETS-induced contraction are of the NK1 type. In the same preparation, the contractile activity of substance P (SP) was slightly more potent than that of neurokinin A (NKA). Unlike in other tissues rich in NK1-receptor subtypes, spantide and L-668, 169 antagonized the contractile response to NKA more effectively than that to SP, and the reverse was observed for L-659, 877. These results strongly suggest that the tachykininergic contraction induced by ETS in the rabbit iris sphincter preparation is mediated by NK1-receptors which are activated by endogenously released NKA.
