Alves-Rodrigues A, Timmerman H, Willems E, Lemstra S, Zuiderveld O P, Leurs R
Leiden/Amsterdam Center for Drug Research, Division of Medicinal Chemistry, Department of Pharmacochemistry, Faculty of Chemistry, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, Netherlands.
Brain Res. 1998 Mar 30;788(1-2):179-86. doi: 10.1016/s0006-8993(97)01537-0.
The purpose of this report was to pharmacologically characterise the histamine H3 in the rat hippocampus using radioligand binding studies with the H3 receptor antagonist [125I]iodophenpropit and the H3 receptor mediated inhibition of [3H]noradrenaline release. A dissociation constant of 0.33 nM and a maximal number of binding sites of 125 fmol/mg protein were found for [125I]iodophenpropit. Competition studies showed stereoselectivity for the (R) and (S) enantiomers of alpha-methylhistamine and 10 microM of GTPgammaS shifted the curve of (R)-alpha-methylhistamine rightwards. Up to 1 microM, (R)-alpha-methylhistamine displaced only 30% whereas the tested H3-antagonists displaced 50-60% of the total [125I]iodophenpropit bound. This indicates the presence of an additional non-H3 receptor binding site(s) for [125I]iodophenpropit in the rat hippocampus. This secondary site shows low affinity for H3 agonists, but high affinity for the tested H3 antagonists. Electrically evoked [3H]acetylcholine release was shown in slices of rat hippocampus. No H3 receptor modulation of [3H]acetylcholine release from hippocampal slices was detectable. However, H3 receptor activation inhibited 42% of the electrically-evoked [3H]noradrenaline release in rat hippocampal slices. The inhibition of [3H]noradrenaline release was effectively antagonized by the H3 antagonists thioperamide and burimamide. We describe the pharmacological identification of the histamine H3 receptor in the rat hippocampus and its similarities and differences from the cortical H3 receptor. These studies enable us to investigate changes in density and functionality of the hippocampal H3 receptor under (patho)physiological conditions.
本报告的目的是通过使用H3受体拮抗剂[125I]碘苯丙哌嗪进行放射性配体结合研究以及H3受体介导的[3H]去甲肾上腺素释放抑制，从药理学角度对大鼠海马体中的组胺H3进行表征。发现[125I]碘苯丙哌嗪的解离常数为0.33 nM，最大结合位点数为125 fmol/mg蛋白质。竞争研究表明，α-甲基组胺的（R）和（S）对映体具有立体选择性，10 μM的GTPγS使（R）-α-甲基组胺的曲线向右移动。高达1 μM时，（R）-α-甲基组胺仅取代了30%，而测试的H3拮抗剂取代了50 - 60%的总结合[125I]碘苯丙哌嗪。这表明大鼠海马体中存在[125I]碘苯丙哌嗪的额外非H3受体结合位点。该次要位点对H3激动剂亲和力低，但对测试的H3拮抗剂亲和力高。在大鼠海马体切片中显示了电诱发的[3H]乙酰胆碱释放。未检测到海马体切片中[3H]乙酰胆碱释放的H3受体调节。然而，H3受体激活抑制了大鼠海马体切片中42%的电诱发[3H]去甲肾上腺素释放。[3H]去甲肾上腺素释放的抑制被H3拮抗剂硫代哌啶和布立马胺有效拮抗。我们描述了大鼠海马体中组胺H3受体的药理学鉴定及其与皮质H3受体的异同。这些研究使我们能够研究在（病理）生理条件下海马体H3受体密度和功能的变化。
