Renouard A, Widdowson P S, Millan M J
Department of Psychopharmacology, Centre de Recherches de Croissy, France.
J Pharmacol Exp Ther. 1994 Sep;270(3):946-57.
In the present study, we examined the binding of the alpha-2 adrenergic receptor (AR) antagonist [3H]-(2-(2-methoxy-1,4-benzodioxan- 2yl)-2-imidazoline ([3H]RX821002) to alpha-2 AR in rat cerebral cortex (CC) and compared the properties of these sites to those of rat alpha-2A (R alpha-2A) AR in submaxillary gland (SMG), human alpha-2A (H alpha-2A) AR in human platelets and alpha-2B AR in neonatal rat lung. In the presence of guanidinium phosphate, [3H]RX821002 bound with high affinity to a large and homogeneous population of sites in CC (Kd = 0.30 +/- 0.03 nM and Bmax = 271 +/- 7 fmol/mg of protein), SMG (Kd = 0.7 and Bmax = 274), human platelets (Kd = 0.6 nM and Bmx = 189) and neonatal rat lung (kd = 0.9 and Bmax = 161). A total of 34 chemically diverse AR ligands monophasically inhibited the binding of [3H]RX821002 from each site with, for the CC, the most potent ligand being atipamezole (Ki = 0.2 nM). For all ligands, and at each site, Hill coefficients did not differ significantly from unity. Although the profiles of inhibition of [3H]RX821002 were virtually identical in rat CC and SMG, these populations revealed several marked differences to human platelets; the alkaloids, rauwolscine and yohimbine, as well as the benzodioxane, [2-(2,6- dimethoxyphenoxyethyl)-aminomethyl-1,4-benzodioxane] (WB 4101), displayed about 10-fold lower affinity for R alpha-2A as compared to H alpha-2A sites, whereas the benzopyrrolidines, fluparoxan and des-fluorofluparoxan, showed about 10-fold greater affinity for R alpha-2A sites. Further, whereas the calculation of potency ratios for selected pairs of ligands, as well as of correlation coefficients, revealed virtual identity between R alpha-2A AR in CC and SMG, these analyses revealed that each of these populations of R alpha-2A AR clearly differed to H alpha-2A AR in human platelets. In addition, both R alpha-2A AR in rat CC and SMG as well as H alpha-2A AR in human platelets markedly differed to alpha-2B AR in neonatal rat lung; thus, they showed 20-fold higher affinity for [2-(2H-(1-methyl-1,3-dihydroisoindole)methyl)-4,5- dihydroimidazoline] (BRL 44408), oxymetazoline, guanfacine and guanabenz yet 10- to 100-fold lower affinity for [2-(2-4-o- methoxyphenyl)piperazine-1-yl)-ethyl)-4,4-dimethyl-1,3-(2H,4H)- isoquinolinedione] (ARC 239) prazosin, chlorpromazine and corynanthine. Similar differences in R alpha-2A and H alpha-2A sites to alpha-2C sites were apparent upon analysis of literature data.(ABSTRACT TRUNCATED AT 400 WORDS)
在本研究中，我们检测了α-2肾上腺素能受体（AR）拮抗剂[3H]-(2-(2-甲氧基-1,4-苯并二恶烷-2-基)-2-咪唑啉（[3H]RX821002）与大鼠大脑皮层（CC）中α-2 AR的结合，并将这些位点的特性与大鼠颌下腺（SMG）中的大鼠α-2A（Rα-2A）AR、人血小板中的人α-2A（Hα-2A）AR以及新生大鼠肺中的α-2B AR的特性进行了比较。在磷酸胍存在的情况下，[3H]RX821002以高亲和力与CC中大量且均一的位点结合（Kd = 0.30±0.03 nM，Bmax = 271±7 fmol/mg蛋白质）、SMG（Kd = 0.7，Bmax = 274）、人血小板（Kd = 0.6 nM，Bmx = 189）和新生大鼠肺（kd = 0.9，Bmax = 161）。总共34种化学结构各异的AR配体单相抑制[3H]RX821002从每个位点的结合，对于CC而言，最有效的配体是阿替美唑（Ki = 0.2 nM）。对于所有配体以及每个位点而言，希尔系数与1无显著差异。尽管[3H]RX821002在大鼠CC和SMG中的抑制曲线几乎相同，但这些群体与人类血小板存在一些显著差异；生物碱、育亨宾碱和利血平，以及苯并二恶烷[2-(2,6-二甲氧基苯氧基乙基)-氨基甲基-1,4-苯并二恶烷]（WB 41）与Hα-2A位点相比，对Rα-2A的亲和力低约10倍，而苯并吡咯烷、氟哌罗生和去氟氟哌罗生对Rα-2A位点的亲和力高约10倍。此外，虽然对选定配体对的效价比以及相关系数的计算显示CC和SMG中的Rα-2A AR之间几乎相同，但这些分析表明这些Rα-2A AR群体中的每一个与人类血小板中的Hα-2A AR明显不同。此外，大鼠CC和SMG中的Rα-2A AR以及人类血小板中的Hα-2A AR与新生大鼠肺中的α-2B AR也有显著差异；因此，它们对[2-(2H-(1-甲基-1,3-二氢异吲哚)甲基)-4,5-二氢咪唑啉]（BRL 44408）、羟甲唑啉、胍法辛和胍那苄的亲和力高20倍，但对[2-(2-4-邻甲氧基苯基)哌嗪-1-基)-乙基)-4,4-二甲基-1,3-(2H,4H)-异喹啉二酮]（ARC 239）、哌唑嗪、氯丙嗪和育亨宾的亲和力低10至100倍。分析文献数据时，Rα-2A和Hα-2A位点与α-2C位点也存在类似差异。（摘要截短至400字）
