一种新的α1A肾上腺素受体选择性拮抗剂—Sertindole

本工作分别在稳定表达α_1A,α_1B和α_1D肾上腺素受体(adrenoceptor,AR)的人胚胎肾脏细胞( human embryonic kidney 293,HEK 293)和大鼠离体血管上,用放射配体结合实验和离体血管收缩功能实验方法以确定sertindole对α₁-AR亚型的选择性拮抗作用。结果显示sertindole与克隆α_1A-AR的亲和性分别是与克隆α_1B-AR和克隆α_1D-AR的69倍和132倍。Sertindole拮抗去甲肾上腺素引起的主动脉和肾动脉收缩反应的pA₂值分别与其对α_1D和α_1A亚型的pKI值相符。分别稳定表达3种亚型受体的HEK293细胞膜标本经与sertindole预温育30min后,受体与¹²⁵IBE2254结合的B_max值显著降低,KD值无显著变化;而在 sertindole 存在条件下,α₁-AR3种亚型与¹²⁵IBE2254 结合的KD值显著增大,但B_max值无显著改变。上述结果表明sertindole为不可逆性竞争性α₁-AR拮抗剂,并有α_1A亚型选择性。     

1-(2,6-二甲氧基)-2-(3,4-二甲基苯乙氨基)丙烷盐酸盐(DDPH)拮抗α1肾上腺素受体的特性

目的　研究DDPH对α1 肾上腺素受体 (α1 AR)及其亚型的拮抗作用。方法　放射配体结合实验和离体血管收缩功能实验。结果　DDPH对12 5I BE2 2 5 4与大鼠脑皮质和脾脏α1 AR结合呈竞争性拮抗作用。pKI 值在两者间无显著性差别 ,Hill系数均接近于 1 0。在分别稳定表达α1A,α1B或α1D AR的克隆HEK2 93细胞中 ,其拮抗的pKI 值α1A和α1D比α1B AR高约 2倍 ,Hill系数均接近于 1 0。并拮抗去甲肾上腺素 (NE)介导大鼠主动脉 ,肾动脉和脾脏收缩的 pA2 值 ,在三者间无显著差别 ,斜率接近 1 0。结论　DDPH对α1 AR有竞争性拮抗作用 ,但其作用对α1 AR亚型无选择性。     

四氢原小檗碱同类物对α1肾上腺素受体的拮抗作用

用放射配体结合实验与离体血管收缩功能实验相结合的方法,研究了4种四氢原小檗碱(tetrahydroproberberine,THPB)同类物对α₁-肾上腺素受体(α₁-AR)的作用。结果显示左旋四氢巴马汀(l-THP),左旋千金藤立陡碱(l-SPD),四氢原小檗碱-18(THPB-18)和四氢小檗碱(THB)¹²⁵IBE2254¹²⁵I-2-β(4-hydroxyphenyl)-ethyaminomethyl-tetralone,¹²⁵IBE)与大鼠脑皮质α₁-AR的结合呈竞争性拮抗作用,pK_I值分别为5.54±0.36,5.56±0.47,5.75±0.56和6.01±0.60,Hill系数接近于1.0。并拮抗苯肾上腺素(phenylephrine,PE)介导大鼠主动脉的收缩,pA₂值分别为5.48±0.58,5.66±0.54,5.64±0.34和5.45±0.76,斜率与1.0无显著性差别。结果提示,4种四氢原小檗碱同类物对α₁-AR均有非亚型选择性拮抗效应,且亲和性相同。     

慢性孵育β-淀粉样肽(25-35)对培养大鼠海马神经元外向钾电流的影响

目的　研究慢性孵育β-淀粉样肽_(25-35) (β-AP_25-35)对海马神经元上瞬时外向钾电流(I_A)和延迟整流钾电流(I_K)的影响。方法　在培养的大鼠海马神经元上用膜片钳全细胞记录钾通道电流。结果　β-AP_25-35 3μmol·L^-1 孵育细胞24h ,I_K 电流幅度增加(44.3±5.4)% ,电流密度由(30.4±6.4)pA·PF^-1 增加至(43.8±4.7)pA·PF^-1 ;β-AP_25-3510μmol·L^-1 孵育12h ,I_K 电流幅度增加(69.8±4.1) % ,电流密度增加至(51.6±7.9)pA·PF^-1,呈浓度依赖性;β-AP_25-35引起的I_K 增加对TEA 5mmol·L^-1 敏感;β-AP_25-35上调I_K 的作用主要发生在β-AP_25-355用药后48h内。β-AP_25-35对I_A无显著性影响。结论　β-AP_25-35选择性地增加海马神经元上I_K,这一作用可能与β-AP的神经毒性有关     

大鼠左心耳三种亚型α1肾上腺素受体对β肾上腺素受体正性变力效应的不同影响

采用电驱动离体大鼠左心耳收缩功能实验研究三种亚型α₁-肾上腺素受体(AR)激动时对β-AR介导正性变力效应的影响. 结果发现,RS 17053(选择性拮抗α_1A-AR)或WB 4101(选择性拮抗α_1A和α_1D-AR)可使去甲肾上腺素(NE)的累积浓度 收缩效应曲线(CRC)显著左移;在BMY 7378(选择性拮抗α_1D-AR)和RS 17053存在下,NE仅激动α_1B和β-AR,其CRC较单独激动β-AR时显著左移;在WB 4101和去氧肾上腺素(Phe)同时存在下(仅激动α_1B-AR),异丙肾上腺素(Iso)的CRC较对照显著左移;用BMY 7378阻断α_1D-AR后,NE的CRC不发生明显的偏移;用RS 17053和螺哌隆阻断α_1A和α_1B-AR,用Phe仅激动α_1D-AR时,对Iso的CRC也无影响. 结果说明在大鼠左心耳α_1A-AR抑制,α_1B-AR增强,而α_1D-AR则不参与对β-AR介导正性变力效应的调节.     

Activation of recombinant h 5-HT1B and h 5-HT1D receptors stably expressed in C6 glioma cells produces increases in Ca2+-dependent K+ current

The putative coupling between stably expressed recombinant h 5-HT_1B or h 5-HT_1D receptors and K⁺ channels which regulate excitability was investigated in C6 glioma cells. Outward K⁺ currents (I _K) were examined in non-transfected C6 glioma cells and in cells expressing cloned h 5-HT_1B or h 5-HT_1D receptors using the patch-clamp technique in the whole-cell configuration. I _K was elicited by a depolarizing step from a holding potential of –60 mV. In C6 glioma cells expressing either recombinant h 5-HT_1B or h 5-HT_1D receptors, sumatriptan similarly increased I _K in a concentration-dependent manner (maximum increase 19.4±7.2%, n=8, P<0.05 and 25.1±3.9%, n=6, P<0.001, respectively) with EC₅₀ values (geometric mean with 95% confidence intervals in parentheses) of 56.3 nM (7.9–140 nM) and 68.7 nM (16–120 nM), respectively. Sumatriptan failed to elicit increases in I _K in non-transfected cells, confirming a specific involvement of the respective membrane h 5-HT_1B and h 5-HT_1D receptors in transfected C6 cells. In the presence of the mixed 5-HT_1B/D receptor antagonist GR 127935 (0.1 μM), sumatriptan (1 μM) failed to significantly increase I _K in C6 cells expressing h 5-HT_1B receptors (–7.5±3.5%, P=NS, n=6), although a higher concentration of GR 127935 (1 μM) was required to significantly inhibit sumatriptan-evoked increases in I _K in C6 cells expressing h 5-HT_1D receptors (–1.8±3.5%, P=NS, n=6), confirming that sumatriptan-evoked responses were indeed mediated by h 5-HT_1B and h 5-HT_1D receptors, respectively. In C6 cells expressing either cloned h 5-HT_1B or h 5-HT_1D receptors, sumatriptan-induced increases in I _K were prevented by the calcium chelator EGTA (5 mM) when included in the patch pipette (maximum increase 0.57±0.6%, n=3, P=NS and –2.8±1.6%, n=5, P=NS, respectively). In C6 cells expressing cloned h 5-HT_1B receptors, sumatriptan (1 μM) similarly failed to significantly increase I _K in the presence of dibutyryl cAMP (10 μM) or when a nominally Ca²⁺-free medium was included in the patch pipette (–19.4±5.1%, n=5 and –5.2±4.3%, n=5, respectively, P=NS in each case). In addition, the Ca²⁺-dependent K⁺ channel blockers iberiotoxin (0.1 μM) and tetraethylammonium (TEA, 1 mM) abolished sumatriptan-induced increases in I _K (–0.5±1.0%, n=4 and –3.9±3.1%, n=4, respectively, P=NS in each case) in C6 cells expressing h 5-HT_1B receptors, confirming the involvement of Ca²⁺-dependent K⁺ channels. In C6 cells expressing cloned h 5-HT_1B receptors, sumatriptan (1 μM) similarly failed to significantly increase I _k after 30-min incubation with thapsigargin (1 μM) or when heparin (2 mg/ml) was included in the patch pipette (1.1±0.4%, n=5 and 1.2±2.4%, n=5, respectively, P=NS). In conclusion, evidence is provided that both recombinant h 5-HT_1B and h 5-HT_1D receptors stably transfected in C6 glioma cells are positively coupled to Ca²⁺-dependent K⁺ channels, and the outward hyperpolarizing current mediated by these channels is dependent upon IP₃ receptor-mediated intracellular Ca²⁺ release. Received: 15 April 1998 / Accepted: 9 September 1998     

硫酸镁对大鼠海马神经元瞬间外向钾电流和延迟整流钾电流的抑制作用

目的研究硫酸镁(MgSO₄)对大鼠海马神经元瞬间外向钾电流(I_A)和延迟整流钾电流(I_K)的作用。方法 全细胞膜片钳技术。结果MgSO₄可浓度依赖地抑制I_A和I_K,半数抑制浓度IC₅₀分别为6.30和7.60 mmol·L^-1;此外还与电压呈依赖性关系,但不具有频率依赖性。6 mmol·L^-1 MgSO₄非常显著地影响I_A和I_K的激活过程,但不改变二者的斜率因子。另外6 mmol·L^-1 MgSO₄还非常显著地影响I_A的失活过程,但不改变其斜率因子。结论 MgSO₄抑制大鼠海马神经元的I_A和I_K,并改变I_A和I_K的激活过程和失活过程。这可能是其抗缺血缺氧引发的中枢神经系统损伤,具有神经保护作用的机制之一。     

抗疟药青蒿素抗心律失常的作用机制

目的：探讨青蒿素抗心律失常的离子电流基础。方法：用全细胞膜片钳技术和双电极电压钳技术。结果：当细胞超极化到-100 mV时,青蒿素以浓度依赖方式明显抑制家兔心室肌细胞I_k1,50μmol.L^-1青蒿素可使家兔心室肌细胞I_k1从对照组的-2.36±0.39　nA减少到-1.43±0.31nA。给予非洲蛙卵母细胞注射K_{ir 2.1}　cRNA后,用不同浓度青蒿素灌注,可减低K_{ir 2.1}钾通道电流,此作用呈电压和浓度依赖性。青蒿素对K_{ir 2.1}钾通道的阻断作用呈可逆性。结论：青蒿素能有效抑制离体心肌细胞I_k1,其抗心律失常作用机理与其抑制心肌细胞I_k1及阻断K_{ir 2.1}通道电流有关。     

吲哚哌啶-哌嗪类衍生物在α1肾上腺素受体介导的收缩反应中的生物学活性

目的 检测一批新合成的α₁-肾上腺素受体(α₁-AR)拮抗剂对α₁-AR的选择性拮抗活性。方法 1 通过吲哚哌啶与哌嗪分子耦合衍生,得到一系列α₁-肾上腺素受体拮抗剂分子,化合物B1~B9,分别具有吲哚哌啶基和不同的取代基团。2 应用离体大鼠左心耳收缩功能实验,检测IPD, 化合物B1~B9对PE刺激下离体大鼠左心耳上α₁-AR的拮抗活性。3 采用Western印迹法检测IPD, 化合物B1~B9对PE刺激下293细胞内细胞外信号调节激酶(ERK)磷酸化水平的影响。结果 1 成功合成了具有吲哚哌啶基和不同取代基团的潜在 α₁-AR拮抗剂。2 提前孵育α₁-AR 拮抗剂酚妥拉明或IPD, 化合物B1, B3, B4, B7, B8, B9, PE引起的离体大鼠左心耳的收缩反应均被有效抑制;其中IPD, 化合物B4和B8引起收缩曲线的明显右移,IPD, 化合物B4和 B8的pA₂值分别是6.72±0.21, 6.86±0.29 和 6.67±0.19。3 在稳定表达α_1A-AR的HEK293细胞内,化合物B1, B2, B3, B5, B6, B7, B8, B9或 IPD均较明显地抑制PE引起的ERK1/2的磷酸化增强;在稳定表达α_1B-AR 的HEK293细胞内,化合物B2, B4, B7或B8较明显地抑制PE引起的ERK1/2的磷酸化增强。 结论 化合物B4能够选择性地拮抗α_1B-AR的活性;化合物B1, B3, B5, B6, B9和 IPD能够选择性地拮抗α_1A-AR的活性。     

1-(2,6-二甲基苯氧基)-2-(3,4-二甲氧基苯乙胺基)丙烷盐酸盐对心脏成纤维细胞胶原I,III型mRNA表达的影响

目的：研究去甲肾上腺素（NE）引起心肌肥厚与胶原I,III型mRNA表达水平之间的关系,及兼具α₁受体阻断作用及钙离子拮抗作用的1-（2,6-二甲基苯氧基）-2-（3,4-二甲氧基苯乙胺基）丙烷盐酸盐（DDPH）的影响。方法：培养的新生鼠心肌成纤维细胞,加NE孵育,胶原I,III型mRNA表达水平用RT-PCR方法测定。结果：心肌成纤维细胞,加1 μmol．L^-1 NE孵育24 h,导致胶原I,III型表达水平分别增加10, 3.1倍,但DDPH可使其表达水平显著降低。 结论：DDPH可抑制心肌成纤维细胞胶原I,III型mRNA的表达。     

Functional α1-adrenergic receptor subtypes in human right gastroepiploic artery

AIM: To study the functional alpha1-adrenergic receptor (alpha1-AR) subtypes in human right gastroepiploic artery (RGA). METHODS: The effects of alpha2-AR, alpha1-AR, and alpha1-AR subtype selective antagonists on norepinephrine (NE)-induced vasoconstriction in isolated human RGA were observed by contractile function experiment. RESULTS: Cumulative concentration-response curves for NE were competitively antagonized in RGA by alpha2-AR selective antagonist yohimbine (pA2 6.82+/-0.28, slope 1.12+/-0.40),alpha1-AR selective antagonist prazosin (pA2 9.77+/-0.22, slope 0.90+/-0.22),alpha1A-AR selective antagonists RS17053 (pA2 8.42+/-0.20, slope 0.93+/-0.20) and 5-MU (pA2 8.42+/-0.22, slope 0.88+/-0.18),alpha1D-AR selective antagonist BMY7378 (pA2 6.84+/-0.32, slope 1.05+/-0.17), and alpha1A-,alpha1B-AR selective antagonist WB4101 (pA2 8.88+/-0.20, slope 1.15+/-0.16). The correlation coefficients between these pA2 values of alpha1-AR selective antagonists with pKi values of which obtained from alpha1A-, alpha1B- and alpha1D-AR cloned cells are 0.95, 0.82, and 0.42. After the vessels were pretreated by chlorethylclonidine (CEC), an alpha1B- and alpha1D-AR irreversible alkylating agent, the pD2 values were changed from 5.9+/-0.5 to 5.6+/-0.6 and the maximal contraction was changed from (8.9+/-3.2) g to (8.0+/-3.2) g, respectively. The difference was not significant. CONCLUSION: In human RGA, the contraction response is mainly mediated by alpha1-AR, of which alpha1A-AR plays an important role, whereas alpha1B- and alpha1D-AR are not involved in the contraction response.     

Does segmental difference in alpha 1-adrenoceptor subtype explain contractile difference in rat abdominal and thoracic aortae?

The cyclooxygenase inhibitor, indomethacin, depresses adrenergic agonist constriction of endothelium-denuded rat abdominal, but not thoracic, aorta. In order to explain this finding, we explored the possibility of segmental differences in the population of alpha 1-adrenoceptor (AR) subtypes. In endothelium-denuded tissues, phenylephrine elicited concentration-dependent contractions in the thoracic and abdominal aortic rings with potencies and maximal effects that, respectively, did not differ significantly (P > .05). Indomethacin (1 x 10(-5) M) inhibited phenylephrine-induced contractions only in abdominal aorta. The subtype-selective alpha 1D-AR antagonist, BMY 7378, was found to antagonize contractions to phenylephrine competitively in abdominal (pA2 8.44) and thoracic (pA2 8.56) aortic rings. These data are consistent with published alpha 1D-AR functional potency and clonal alpha 1D-AR binding affinity. In addition, cumulative concentration-contraction curves for phenylephrine were competitively antagonized in the rat abdominal and thoracic aortae by prazosin, 5-methylurapidil and WB 4101, with pA2 values of 9.39 and 9.61, 7.64 and 7.85, and 9.43 and 9.58, respectively. These compounds with varying degrees of subtype selectivity inhibited contractions of the thoracic and abdominal aortae with affinities consistent with those determined at the alpha 1D-AR subtype. The results of this study suggest that the contraction to phenylephrine of the rat abdominal and thoracic aorta is mediated via the same alpha 1D-AR subtype.     

In vitro alpha1-adrenoceptor pharmacology of Ro 70-0004 and RS-100329, novel alpha1A-adrenoceptor selective antagonists.

It has been hypothesized that in patients with benign prostatic hyperplasia, selective antagonism of the alpha1A-adrenoceptor-mediated contraction of lower urinary tract tissues may, via a selective relief of outlet obstruction, lead to an improvement in symptoms. The present study describes the alpha1-adrenoceptor (alpha1-AR) subtype selectivities of two novel alpha1-AR antagonists, Ro 70-0004 (aka RS-100975) and a structurally-related compound RS-100329, and compares them with those of prazosin and tamsulosin. Radioligand binding and second-messenger studies in intact CHO-K1 cells expressing human cloned alpha1A-, alpha1B- and alpha1D-AR showed nanomolar affinity and significant alpha1A-AR subtype selectivity for both Ro 70-0004 (pKi 8.9: 60 and 50 fold selectivity) and RS-100329 (pKi 9.6: 126 and 50 fold selectivity) over the alpha1B- and alpha1D-AR subtypes respectively. In contrast, prazosin and tamsulosin showed little subtype selectivity. Noradrenaline-induced contractions of human lower urinary tract (LUT) tissues or rabbit bladder neck were competitively antagonized by Ro 70-0004 (pA2 8.8 and 8.9), RS-100329 (pA2 9.2 and 9.2), tamsulosin (pA2 10.4 and 9.8) and prazosin (pA2 8.7 and 8.3 respectively). Affinity estimates for tamsulosin and prazosin in antagonizing alpha1-AR-mediated contractions of human renal artery (HRA) and rat aorta (RA) were similar to those observed in LUT tissues, whereas Ro 70-0004 and RS-100329 were approximately 100 fold less potent (pA2 values of 6.8/6.8 and 7.3/7.9 in HRA/RA respectively). The alpha1A-AR subtype selectivity of Ro 70-0004 and RS-100329, demonstrated in both cloned and native systems, should allow for an evaluation of the clinical utility of a 'uroselective' agent for the treatment of symptoms associated with benign prostatic hyperplasia.     

介导大鼠肠系膜动脉血管床收缩反应的α1—肾上腺素受体亚型特征

目的：研究去甲肾上腺素（ＮＥ）介导大鼠肠系膜血管床（ＭＶＢ）收缩的α在－肾上腺素受体（α１－ＡＲ）亚型,方法：用灌流大鼠ＭＶＢ标本收缩功能实验和克隆细胞放射配体结合实验测定α１－ＡＲ亚型选择性拮抗剂ｐＡ２和ｐＫｉ,并作相关分析。结果：α１Ａ－ＡＲ选择性拮抗剂ＲＳ－１７０５３,ＷＢ４１０１,５－ＭＵ及α１Ｄ－ＡＲ选择性拮抗剂ＢＭＹ７３７８的ｐＡ２分别为８．９８±０．２８,９．１６±０．２０,８．６９     

Glycogen phosphorylase activation by two different alpha 1-adrenergic receptor subtypes: methoxamine selectively stimulates a putative alpha 1-adrenergic receptor subtype (alpha 1a) that couples with Ca2+ influx

We compared the effects of methoxamine on alpha 1-adrenergic receptor-mediated phosphorylase activation in rat hepatocytes and rabbit aorta. Although methoxamine is a potent agonist in activating phosphorylase of rabbit aorta, it had little effect in rat hepatocytes. Using the phenoxybenzamine inactivation method, we found that the quantitative relationship between 125I-BE2254 (125I-BE) binding capacity and maximal norepinephrine-stimulated phosphorylase activation was nonlinear in rabbit aorta, whereas it was linear in rat hepatocytes. The potency of methoxamine in inhibiting specific 125I-BE binding is significantly (p less than 0.05) higher in rabbit aorta (Kd, 96.4 +/- 7.7 microM), compared with rat hepatocytes (Kd, 283 +/- 16 microM). However, these quantitative differences could not fully explain the blunted [Ca2+]c and phosphorylase responses to methoxamine in rat hepatocytes. Treatment with chlorethylclonidine dose dependently suppressed 125I-BE binding sites and norepinephrine-induced phosphorylase activation in rat hepatocytes, whereas in rabbit aorta it resulted in only a 31% decrease in 125I-BE binding sites, with little effect on phosphorylase activation. Furthermore, alpha 1-adrenergic receptor-mediated cellular events of phosphatidylinositol (PI) hydrolysis and phosphorylase activation were unaffected by the removal of extracellular Ca2+ in rat hepatocytes, whereas both responses were markedly attenuated in rabbit aorta. The results indicate that two different alpha 1-adrenergic receptor subtypes activate glycogen phosphorylase, through different mechanisms for increasing [Ca2+]c in the two systems. In rat hepatocytes, alpha 1 receptors are closely linked to PI hydrolysis and Ca2+ release from intracellular stores and cause phosphorylase activation. In rabbit aorta, on the other hand, activation of alpha 1 receptors increases [Ca2+]c by Ca2+ influx from the extracellular fluid as well as by Ca2+ release, and both PI hydrolysis and phosphorylase activation are caused mainly by the Ca2+ entry. Methoxamine interacts with both chlorethylclonidine-sensitive and -insensitive alpha 1 receptor subtypes but selectively stimulates the alpha 1 receptor subtype that closely couples with the Ca2+ influx.     

1-(2,6-二甲基苯氧基)-2-(3,4-二甲氧基苯乙氨基)丙烷盐酸盐对大鼠心脏α_1受体的影响

DDPH 3 mg/kg对毁脊髓大鼠有拮抗甲氧胺升高左心室压力及室内压最大变化速率(±dP/dt_(max))、左室舒张末期压、血压和心率的作用;在大鼠离体工作心脏上,有普萘洛尔存在时,DDPH 1～10μmol/L有阻断苯福林升高左心室压力及dP/dt_(max)、主动脉流量和心率的作用;DDPH60μmol/L灌流大鼠在体心肺,有取消甲氧明提高左心室压力和心输出量的作用。DDPH尚可显著减慢大鼠工作心脏和在体心肺装置的心率。上述结果提示DDPH对血管平滑肌及心肌的α_1受体有阻断作用。     

1-(2,6-二甲基苯氧基)-2-(3，4-二甲氧基苯乙氨基)丙烷盐酸盐对心肌肥厚大鼠左心室N- ras, P53 mRNA表达的影响

为研究1-(2，6-二甲基苯氧基)-2-(3，4-二甲氧基苯乙氨基)丙烷盐酸盐(DDPH)对心肌肥厚的逆转作用，用部分狭窄腹主动脉方法造成大鼠心肌肥厚模型，从术后wk 4开始，ig DDPH 25和50 mg·kg^-1·d^-1，持续8 wk. 术后12 wk，各组大鼠体重无显著性差异，但模型组心重/体重，左心室重/全心重明显高于对照组. 模型组心肌组织N-ras mRNA表达比对照组高，而抑癌基因P53 mRNA表达明显低于对照组，DDPH可逆转上述变化. 表明DDPH可逆转腹主动脉狭窄所致心肌肥厚.     

(-)-Discretamine, a selective alpha 1D-adrenoceptor antagonist, isolated from Fissistigma glaucescens.

1. The selectivity of (-)-discretamine for alpha 1-adrenoceptor subtypes was investigated by use of functional and binding studies in rat vas deferens, spleen and aorta, and in cultured DDT1MF-2 and A10 cells. 2. In prostatic portions of rat vas deferens, the competitive antagonists (-)-discretamine, 5-methylurapidil (5-MU) and prazosin inhibited contractions to noradrenaline (NA) with pA2 values of 6.21, 8.71 and 9.27, respectively. The irreversible antagonist, chloroethylclonidine (CEC, 100 microM) failed to affect contractions to NA while nifedipine (1 microM) blocked them almost completely. 3. In rat spleen, the competitive antagonists (-)-discretamine, 5-MU and prazosin inhibited contractions to phenylephrine with pA2 values of 6.44, 7.19 and 9.45, respectively. CEC (100 microM) significantly reduced the maximum contraction to phenylephrine while nifedipine (1 microM) did not affect it. 4. In rat aorta, the competitive antagonists (-)-discretamine, 5-MU and prazosin inhibited contractions to NA with pA2 values of 7.60, 8.00 and 9.40, respectively. CEC also antagonized the contractions to NA in a competitive manner with a pA2 value of 6.10. 5. The specific binding of [3H]-prazosin to DDT1MF-2 and A10 cells was concentration-dependent and saturated at 3-5 nM with KD values of 0.24 +/- 0.02 and 0.20 +/- 0.02 nM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

ABT-866, a novel alpha(1A)-adrenoceptor agonist with antagonist properties at the alpha(1B)- and alpha(1D)-adrenoceptor subtypes

N-[3-(1H-Imidazol-4-ylmethyl)phenyl]ethanesulfonamide, maleate (ABT-866) is a novel alpha(1)-adrenoceptor agent with mixed pharmacological properties in vitro. Compared to phenylephrine, ABT-866 demonstrates intrinsic activity at the alpha(1A)-adrenoceptor subtype present in the rabbit urethra (pD(2) = 6.22, with 80% of the phenylephrine response), reduced intrinsic activity at the alpha(1B)-adrenoceptor subtype in the rat spleen (pD(2)= 6.16, with 11% of the phenylephrine response), and no intrinsic activity at the rat aorta alpha(1D)-adrenoceptor subtype. ABT-866 also demonstrated antagonism at the rat spleen alpha(1B)-adrenoceptor (pA(2) = 5.39 +/- 0.08, slope = 1.20 +/- 0.12), and the rat aorta alpha(1D)-adrenoceptor (pA(2)= 6.18 +/- 0.09, slope = 0.96 +/- 0.13). This is in contrast to the weak non-selective activity seen with the alpha(1)-adrenoceptor agonist, phenylpropanolamine (2-amino-1-phenyl-1-propanol hydrochloride), and the alpha(1A/D)-adrenoceptor selective agonist 1-(2',5'-dimethoxyphenyl)-2-aminoethanol hydrochloride (ST-1059), the active metabolite of midodrine, that has been used clinically for the treatment of stress urinary incontinence. This study identifies a unique agent that may prove to be a valuable in vivo tool in testing the hypothesis that the alpha(1A)-adrenoceptor can be stimulated to contract the smooth muscle present in the urethra without evoking blood pressure elevations presumably caused by alpha(1B)- and alpha(1D)-adrenoceptor subtype involvements in the vasculature.