Findell P R, Torkelson S M, Craig J C, Weiner R I
Reproductive Endocrinology Center, University of California, San Francisco 94143.
Mol Pharmacol. 1988 Jan;33(1):78-83.
The flexible dopamine (DA) molecule exists in one or the other of its two conformational extremes (alpha- or beta-rotamer) and its receptor in the anterior pituitary gland exists in a high and a low affinity state. A series of novel, rigid DA congeners (2-substituted octahydrobenzo[f]quinolines) was synthesized and used to investigate the conformation of DA preferred by its anterior pituitary receptor and the significance of recognition of the two affinity states to the inhibition of prolactin (PRL) secretion. Analysis of competition curves of congeners for [3H]spiperone binding to bovine anterior pituitary membranes was used to calculate affinity constants. Congeners in the beta-rotamer conformation showed a biphasic competition curve as observed for DA. The curves were resolved into high (nM) and low (microM) affinity binding sites. This biphasic binding could be converted to monophasic low affinity binding in the presence of a nonhydrolyzable GTP analog. The congeners in the alpha-rotameric conformation showed monophasic low affinity binding. The potency of congeners to suppress PRL release was evaluated in cell cultures of dispersed bovine anterior pituitary. Congeners recognizing the high affinity binding site were 100-fold more potent in suppressing PRL release than those recognizing only low affinity binding sites. Dihydroxy congeners versus monohydroxy congeners and cyanomethyl group substituted versus methylthiomethyl substituted congeners occupied greater proportions of high affinity binding sites. Increasing proportions of high affinity sites occupied increased the potency of the congener to suppress PRL release. These results suggest that the beta-rotameric conformational extreme of DA is preferred by its receptor in the anterior pituitary gland and that the high affinity state of this receptor is functionally important in mediating the inhibition of PRL secretion.
柔性多巴胺（DA）分子以其两种构象极端形式（α-或β-旋转异构体）之一存在，其在前叶垂体中的受体存在高亲和力和低亲和力两种状态。合成了一系列新型的刚性DA类似物（2-取代八氢苯并[f]喹啉），并用于研究前叶垂体受体偏好的DA构象，以及识别两种亲和力状态对抑制催乳素（PRL）分泌的意义。通过分析类似物与[3H]螺哌隆结合牛前叶垂体膜的竞争曲线来计算亲和力常数。β-旋转异构体构象的类似物显示出与DA观察到的双相竞争曲线。这些曲线可分解为高亲和力（nM）和低亲和力（μM）结合位点。在不可水解的GTP类似物存在下，这种双相结合可转变为单相低亲和力结合。α-旋转异构体构象的类似物显示单相低亲和力结合。在分散的牛前叶垂体细胞培养物中评估类似物抑制PRL释放的效力。识别高亲和力结合位点的类似物在抑制PRL释放方面的效力比仅识别低亲和力结合位点的类似物高100倍。二羟基类似物与单羟基类似物相比，以及氰甲基取代的类似物与甲硫基甲基取代的类似物占据更高比例的高亲和力结合位点。占据的高亲和力位点比例增加会提高类似物抑制PRL释放的效力。这些结果表明，DA的β-旋转异构体构象极端是其在前叶垂体中的受体所偏好的，并且该受体的高亲和力状态在介导PRL分泌的抑制中具有重要功能。
