Regoli D, Drapeau G, Dion S, D'Orléans-Juste P
Department of Pharmacology, Medical School, University of Sherbrooke, Canada.
Pharmacology. 1989;38(1):1-15. doi: 10.1159/000138512.
The most widely used smooth muscle preparations for neurokinin bioassays have been critically analyzed in order to determine whether neurokinins act directly or by the intermediary of other natural agents. Indeed, part of the contraction of the GPI in response to neurokinins appears to be mediated by acetylcholine and possibly prostaglandins. Active metabolites of the arachidonic acid cascade also intervene in the response of the HUB. Neurokinins produce relaxation of the DCA by stimulating the release of a vascular smooth muscle relaxing factor from the endothelium. In the other preparations (the RD, the RPA without endothelium and the RPV) neurokinins may act directly on the smooth muscle fibers. Neurokinins produce their biological effects by activating specific receptors. Three different receptor types, one for each mammalian neurokinin, have been identified by using four groups of natural peptide sequences and some selective agonists. The receptor for SP is particularly sensitive to SP and physalaemin and shows higher affinity for the whole natural peptides (SP, NKA) than for their C-terminal fragments. The receptor for neurokinin A is highly sensitive to NKA and eledoisin: it shows high affinity for heptapeptide fragments such as NKA4-10 and SP5-11. The receptor for NKB is sensitive to NKB and kassinin more than to the other natural peptides and their fragments. The natural peptides show however little selectivity. Synthetic analogues active on a single receptor type (selective agonists) have been used to find out whether the responses of the isolated organs are due to the activation of one or more than one receptor. It has been found that the GPI, the RD and the HUB contain all three or at least two receptors, while the DCA has only the NK1, the RPA has only the NK2 and the RPV only the NK3 type. Binding sites specific for each neurokinin have been identified in brain and peripheral organs with accurate biochemical assays, using labeled neurokinins. Competitive displacement assays have been performed with a variety of neurokinin-related peptides, and their Ki have been determined. By plotting Ki values against the ED50, estimated from biological assays, positive significant correlations have been found for the monoreceptor (DCA, RPA, RPV) but not for the multiple receptor systems (GPI, RD, HUB). This suggests that pharmacological receptors may be identical with the recognition sites which bind the labeled neurokinins. The availability of monoreceptor systems and of selective agonists opens the way for the identification of potential antagonists and accurate estimation of their affinities.(ABSTRACT TRUNCATED AT 250 WORDS)
为了确定神经激肽是直接起作用还是通过其他天然介质起作用，对神经激肽生物测定中最广泛使用的平滑肌制剂进行了严格分析。实际上，豚鼠回肠纵肌（GPI）对神经激肽反应的部分收缩似乎是由乙酰胆碱和可能的前列腺素介导的。花生四烯酸级联反应的活性代谢产物也参与了豚鼠膀胱（HUB）的反应。神经激肽通过刺激内皮细胞释放一种血管平滑肌舒张因子，使去甲肾上腺素能结肠（DCA）舒张。在其他制剂（兔十二指肠（RD）、无内皮的兔肺动脉（RPA）和兔门静脉（RPV））中，神经激肽可能直接作用于平滑肌纤维。神经激肽通过激活特定受体产生生物学效应。通过使用四组天然肽序列和一些选择性激动剂，已鉴定出三种不同的受体类型，每种哺乳动物神经激肽对应一种。P物质（SP）受体对SP和蛙皮素特别敏感，对整个天然肽（SP、神经激肽A（NKA））的亲和力高于对其C末端片段的亲和力。神经激肽A受体对NKA和eledoisin高度敏感：它对七肽片段如NKA4 - 10和SP5 - 11显示出高亲和力。神经激肽B（NKB）受体对NKB和蛙皮缩胆囊素比对其他天然肽及其片段更敏感。然而，天然肽的选择性很小。已使用对单一受体类型有活性的合成类似物（选择性激动剂）来确定离体器官的反应是由于一种还是多种受体的激活。已发现GPI、RD和HUB含有所有三种或至少两种受体，而DCA仅含有NK1受体，RPA仅含有NK2受体，RPV仅含有NK3受体。使用标记的神经激肽，通过精确的生化测定在脑和外周器官中鉴定了每种神经激肽的特异性结合位点。已用多种与神经激肽相关的肽进行了竞争性置换测定，并确定了它们的抑制常数（Ki）。通过将Ki值与从生物学测定估计的半数有效剂量（ED50）作图，发现单受体（DCA、RPA、RPV）有显著正相关，而多受体系统（GPI、RD、HUB）则没有。这表明药理学受体可能与结合标记神经激肽的识别位点相同。单受体系统和选择性激动剂的可用性为鉴定潜在拮抗剂及其亲和力的准确估计开辟了道路。（摘要截短于250字）
