Low A M, Lu-Chao H, Wang Y F, Brown R D, Kwan C Y, Daniel E E
Department of Biomedical Sciences, McMaster University, Hamilton, ON, Canada.
J Pharmacol Exp Ther. 1998 May;285(2):894-901.
In this study, the effects of nine alpha-1 adrenoceptor antagonists [prazosin, WB 4101 (WB), chloroethylclonidine (CEC), 5-methylurapidil (5-MU), BMY 7378 (BMY), MDL 73005EF (MDL73), MDL 72832 (MDL72), RS 17053 (RS) and SK&F 105854 (SKF)] were studied on contractile responses to phenylephrine (PE) of the endothelium-denuded dog aorta in vitro. All antagonists, except CEC, 5-MU and RS, produced concentration-dependent competitive inhibition of contractile responses of the aorta to PE. The rightward shift of the concentration-response curves of PE yielded constant pKB values with increasing antagonist concentrations in most cases allowing a single pooled value to be determined: for prazosin, a pKB of 8.99 +/- 0.11 (n = 20, KB of 1.03 nM); for WB, a pKB of 8.75 +/- 0.08 (n = 23, KB of 1.76 nM); for BMY, a pKB of 7.21 +/- 0.13 (n = 13, KB of 62 nM); for MDL72, a pKB of 7.95 +/- 0.15 (n = 12, KB of 11.2 nM); and for SK&F 105854, a pKB of 5.82 +/- 0.08 (n = 15, KB of 1.52 microM). For MDL73, pKB values decreased with antagonist concentration: 7.88 +/- 0.06 at 10 nM, 7.56 +/- 0.28 at 100 nM and 6.92 +/- 0.18 at 1000 nM, which suggests the presence of more than one receptor subtype. CEC (10 and 100 microM) almost completely inhibited responses to PE; lower concentrations had no significant effect. 5-MU (10-300 nM) and RS (3-300 nM) were ineffective antagonists in this tissue. Because WB, a highly selective alpha-1D and alpha-1A adrenoceptor subtypes inhibitor, blocked PE responses (with less affinity than for alpha-1A adrenoceptors), and 5-MU and RS, which are selective blockers for alpha-1A adrenoceptor, were ineffective, we conclude that alpha-1A adrenoceptors are absent in the dog aorta. The effects of the less selective MDL72 were inconsistent with actions at alpha-1B or alpha-1D adrenoceptors. Although WB shifted the PE concentration-response curve to the right, the abilities of BMY, MDL73 and SKF to inhibit competitively PE contraction were of lower affinity compared with expectations for interaction with alpha-1D adrenoceptors; they are not the predominant subtype. The complete inhibition of PE responses by CEC suggests that the dog aorta contains the alpha-1B adrenoceptor subtype. In immunocytochemical studies of the expression of alpha-1B adrenoceptor, all cells apparently expressed this protein. Moreover, Western blot studies of the microsomal fractions confirmed the presence of alpha-1B adrenoceptors. In the dog aorta, the alpha-1 adrenoceptors predominantly resemble alpha-1B rather than alpha-1D adrenoceptors as reported in the rat aorta.
在本研究中，研究了9种α-1肾上腺素能受体拮抗剂[哌唑嗪、WB 4101（WB）、氯乙可乐定（CEC）、5-甲基乌拉地尔（5-MU）、BMY 7378（BMY）、MDL 73005EF（MDL73）、MDL 72832（MDL72）、RS 17053（RS）和SK&F 105854（SKF）]对去内皮犬主动脉对去氧肾上腺素（PE）的收缩反应的影响。除CEC、5-MU和RS外，所有拮抗剂均对主动脉对PE的收缩反应产生浓度依赖性竞争抑制。在大多数情况下，随着拮抗剂浓度增加，PE浓度-反应曲线右移产生恒定的pKB值，从而可以确定单个汇总值：对于哌唑嗪，pKB为8.99±0.11（n = 20，KB为1.03 nM）；对于WB，pKB为8.75±0.08（n = 23，KB为1.76 nM）；对于BMY，pKB为7.21±0.13（n = 13，KB为62 nM）；对于MDL72，pKB为7.95±0.15（n = 12，KB为11.2 nM）；对于SK&F 105854，pKB为5.82±0.08（n = 15，KB为1.52 μM）。对于MDL73，pKB值随拮抗剂浓度降低：10 nM时为7.88±0.06，100 nM时为7.56±0.28，1000 nM时为6.92±0.18，这表明存在不止一种受体亚型。CEC（10和100 μM）几乎完全抑制对PE的反应；较低浓度无显著影响。5-MU（10 - 300 nM）和RS（3 - 300 nM）在该组织中是无效拮抗剂。因为高度选择性的α-1D和α-1A肾上腺素能受体亚型抑制剂WB阻断了PE反应（亲和力低于α-1A肾上腺素能受体），而选择性α-1A肾上腺素能受体阻滞剂5-MU和RS无效，我们得出结论，犬主动脉中不存在α-1A肾上腺素能受体。选择性较低的MDL72的作用与α-1B或α-1D肾上腺素能受体的作用不一致。尽管WB使PE浓度-反应曲线右移，但与预期的与α-1D肾上腺素能受体相互作用相比，BMY、MDL73和SKF竞争性抑制PE收缩的能力亲和力较低；它们不是主要亚型。CEC对PE反应的完全抑制表明犬主动脉含有α-1B肾上腺素能受体亚型。在α-1B肾上腺素能受体表达的免疫细胞化学研究中，所有细胞显然都表达这种蛋白。此外，微粒体部分的蛋白质印迹研究证实了α-1B肾上腺素能受体的存在。在犬主动脉中，α-1肾上腺素能受体主要类似于α-1B而非大鼠主动脉中报道的α-1D肾上腺素能受体。
