Characterization of subtype of α_1-adrenoceptor mediating vasoconstriction in perfused rat mesenteric vascular bed

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α１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±００２和６０３±０２６,Ｓｃｈｉｌｄ作图斜率值与１０差别无显著性．其ｐＡ２值与α１ＡＡＲ的ｐＫｉ相关系数为０９７,与α１Ｂ和α１ＤＡＲ的相关系数分别为０５２和００４．结论：介导外源性ＮＥ收缩大鼠ＭＶＢ的功能性受体为α１ＡＡＲ     

12月龄与3月龄大鼠心脏α1肾上腺素受体亚型的比较

采用［１２５Ｉ］ＢＥ２２５４放射配体结合实验和离体灌流左心房收缩功能实验，比较１２月龄与３月龄大鼠心脏α１肾上腺素受体（α１－ＡＲ）三种亚型分布及其介导的正性变力效应的差别．结果显示与３月龄大鼠相比，１２月龄大鼠：（１）心脏α１－ＡＲ最大结合容量显著减少；去甲肾上腺素（ＮＥ）通过激动α１－ＡＲ引起的左心房累积浓度－收缩效应曲线显著右移；（２）（＋）尼古地平，ＢＭＹ７３７８和ＷＢ４１０１的高亲和性位点所占百分比显著下降；（３）氯乙基可乐定预处理使ＮＥ引起的左心房最大收缩效应的下降幅度，以及舍吲哚，ＢＭＹ７３７８和ＷＢ４１０１拮抗ＮＥ介导正性变力效应的ｐＡ２值均无显著差异．提示１２月龄大鼠较３月龄大鼠心脏α１－ＡＲ总数减少，且以α１Ａ－和α１Ｄ－ＡＲ亚型更为显著；α１－ＡＲ介导的正性变力效应明显降低，α１Ｂ－ＡＲ的功能效率降低最为明显．     

长期饮用普萘洛尔对大鼠心脏α_1肾上腺素受体亚型数量的影响

采用放射配体结合实验，离体左心房收缩功能实验及逆转录聚合酶链反应等方法观察大鼠长期饮用非选择性β肾上腺素受体拮抗剂普萘洛尔（７０ｍｇ·ｋｇ－１·ｄ－１，８ｗｋ）对心脏α１肾上腺素受体（α１－ＡＲ）亚型分布及其功能的影响．结果表明大鼠饮用普萘洛尔８ｗｋ后心脏α１－ＡＲ总数量无显著变化，ＷＢ４１０１和尼古地平竞争抑制曲线两位点分析结果显示３种亚型受体所占比例发生了明显变化，α１Ａ－ＡＲ数量不变，α１Ｂ－ＡＲ数量减少，α１Ｄ－ＡＲ数量增加，α１－ＡＲ亚型ｍＲＮＡ水平的改变为α１Ａ－ＡＲ和α１Ｄ－ＡＲ显著增加，α１Ｂ－ＡＲ明显减少．但α１－ＡＲ３种亚型介导去甲肾上腺素正性变力效应的作用无显著改变．     

大鼠左心耳三种亚型α_1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,ＲＳ１７０５３（选择性拮抗α１Ａ－ＡＲ）或ＷＢ４１０１（选择性拮抗α１Ａ－和α１Ｄ－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α１Ｄ－ＡＲ）和ＲＳ１７０５３ 存在下,ＮＥ仅激动α１Ｂ－和β－ＡＲ,其ＣＲＣ较单独激动β－ＡＲ 时显著左移;在ＷＢ４１０１ 和去氧肾上腺素（Ｐｈｅ）同时存在下（仅激动α１Ｂ－ＡＲ）,异丙肾上腺素（Ｉｓｏ）的ＣＲＣ较对照显著左移;用ＢＭＹ ７３７８ 阻断α１Ｄ－ＡＲ后,ＮＥ的ＣＲＣ不发生明显的偏移;用ＲＳ１７０５３ 和螺哌隆阻断α１Ａ－和α１Ｂ－ＡＲ,用Ｐｈｅ 仅激动α１Ｄ－ＡＲ 时,对Ｉｓｏ 的ＣＲＣ也无影响． 结果说明在大鼠左心耳α１Ａ－ＡＲ抑制,α１Ｂ－ＡＲ 增强,而α１Ｄ－ＡＲ则不参与对β－ＡＲ 介导正性变力效应的调节．     

长期饮用普萘洛尔对大鼠心脏和血淋巴细胞β肾上腺素受体效应及亚型的影响

采用放射配体结合实验，离体左心房收缩功能实验，逆转录聚合酶链反应及高效液相色谱等方法研究长期饮用普萘洛尔（７０ｍｇｋｇ－１ｄ－１，８ｗｋ）对大鼠心脏β肾上腺素受体（β－ＡＲ）及其亚型，外周血淋巴细胞β２－ＡＲ和血浆儿茶酚胺水平的影响．结果表明长期饮用普萘洛尔后：（１）心脏β－ＡＲ密度从对照组的４１±８ｐｍｏｌｇ－１蛋白上调到６１±９ｐｍｏｌｇ－１蛋白，ＣＧＰ２０７１２Ａ竞争抑制曲线２位点分析结果显示为β１和β２－ＡＲ同等程度上调；（２）心脏β１－ＡＲｍＲ－ＮＡ水平不变而β２－ＡＲｍＲＮＡ水平显著增加；（３）β－ＡＲ及其亚型介导的离体左心房正性变力效应增强，以β２－ＡＲ的功能改变更为显著；（４）血淋巴细胞β２－ＡＲ数目从对照组的１９±７ｐｍｏｌｇ－１蛋白上调至３２±８ｐｍｏｌｇ－１蛋白；（５）血浆去甲肾上腺素水平（０．２１±０．１２μｇＬ－１）明显低于对照组（０．３８±０．１５μｇＬ－１）．     

甲基黄酮醇胺对离体豚鼠气管的作用

本文比较性研究甲基黄酮醇胺盐酸盐（ＭＦＡ），三氟拉嗪（Ｔｒｉ），维拉帕米（Ｖｅｒ），氨茶碱（Ａｍｉ）和异丙肾上腺素（Ｉｓｏ）对豚鼠离体气管的舒张作用．ＭＦＡ（０．１－０．３ｍｍｏｌ·Ｌ－１）时间依赖性舒张ＫＣｌ诱导的气管平滑肌收缩。低于０．１ｍｍｏｌ·Ｌ－１时ＭＦＡ对ＫＣｌ诱导的收缩仅有轻微作用，却使Ｉｓｏ和Ａｍｉ的浓度舒张曲线明显向左上移动。ＭＦＡ，Ｖｅｒ，Ｔｒｉ使ＣａＣｌ２量效曲线向右下移，ｐＤ２值分别为：５．０±ｓ０．５，６．４±ｓ０．８，５．０±ｓ０．６．ＭＦＡ，Ｖｅｒ，Ｔｒｉ，Ａｍｉ剂量依赖性抑制次大量生理激动剂所致的收缩，其作用强度顺序为：Ｔｒｉ＞Ｖｅｒ＝ＭＦＡ＞Ａｍｉ．提示ＭＦＡ具有非竞争性钙拮抗作用，其作用方式与Ｔｒｉ相似。与Ａｍｉ相比、ＭＦＡ是一个较强的主气管扩张剂，并与Ａｍｉ，Ｉｓｏ具有明显的协同舒张支气管作用。     

延髓腹外侧头端注射莫索尼定对大鼠血压,心率和肾交感神经放电…

目的：观察延髓腹外侧头端（ＲＶＬＭ）注射莫索尼定（Ｍｏｘ）对麻醉大鼠血压（ＢＰ）、心率（ＨＲ）及肾交感神经放电（ＲＳＮＡ）的影响。方法：麻醉大鼠ＲＶＬＭ注射１μＬ Ｍｏｘ１，１０，１００μｍｏｌ·Ｌ＾－１，同步记录ＢＰ，ＨＲ及ＲＳＮＡ。结果：Ｍｏｘ１，１０，１００μｍｏｌ·Ｌ＾－１分别使ＢＰ从１３．９±１．０ｋＰａ降至１３．０±１．７ｋＰａ（Ｐ〈０．０５），１３．８±１．８ｋＰａ至１１．４±１．５     

EDRF对NE引起的大鼠主动脉缩血管效应的作用

目的：研究ＥＤＲＦ（ｅｎｄｏｔｈｅｌｉｕｍ－ｄｅｒｉｖｅｄｒｅｌａｘｉｎｇｆａｃｔｏｒ，ＥＤＲＦ）对ＮＥ（ｎｏｒｅｐｉｎｅｐｈｒｉｎｅ，ＮＥ）引起的大鼠主动脉收缩反应的影响。方法：内皮完整和去内皮的大鼠主动脉环悬挂在器官浴槽中，测定血管的张力和收缩速度的变化。所有的实验在吲哚美辛（ｉｎｄｏｍｅｔｈａｃｉｎ，１０μｍｏｌ·Ｌ－１）和普萘洛尔（ｐｒｏｐｒａｎｏｌｏｌ，３μｍｏｌ·Ｌ－１）存在下进行。结果：用甲烯蓝（ｍｅｔｈｙｌｅｎｅｂｌｕｅ，ＭＢ，１０μｍｏｌ·Ｌ－１）和左旋硝基精氨酸（ＮＧ－ｎｉｔｒｏ－Ｌ－ａｒｇｉｎｉｎｅ，Ｌ－ＮＮＡ，３０μｍｏｌ·Ｌ－１）处理内皮完整的大鼠主动脉环，ＮＥ的剂量－收缩曲线明显左移。ＥＣ３０值均降低７倍，最大反应比值分别为１．６±０．３和１．７±０．４。在去内皮的大鼠主动脉环中，经ＭＢ与Ｌ－ＮＮＡ处理后，仍可见ＥＣ３０下降３倍，最大反应比值分别为１．１±０．６和１．１±０．４。后者可能与血管平滑肌产生少量ＥＤＲＦ有关。结论：结果提示，ＮＥ对血管的收缩反应也受血管内皮和平滑肌产生的ＥＤＲＦ的调控。     

α_1肾上腺素受体激动剂的亚型选择性

采用放射配基竞争抑制实验和收缩功能实验相结合的方法，比较几种α１肾上腺素受体（α１－ＡＲ）激动剂对α１－ＡＲ两种亚型亲和性的异同，在放射配基竞争抑制实验中，以氯乙基可乐定预温育的海马粗制细胞膜标本中的α１－ＡＲ代表α１Ａ－ＡＲ亚型，以纯化的肝细胞膜标本中的α１－ＡＲ代表α１Ｂ－ＡＲ亚型，显示去甲肾上腺素，苯福林和Ａ５７２１９对两种α１－ＡＲ亚型的ｐＫｉ值无明显差异，而甲氧明和羟甲唑啉对α１Ａ－ＡＲ亚型的ｐＫｉ值显著大于α１Ｂ－ＡＲ亚型，离体血管收缩实验中，以氯乙基可乐定预温育的肾动脉和硝苯地平存在下的主动脉中，α１－ＡＲ介导的收缩分别代表α１Ａ－和α１Ｂ－ＡＲ亚型介导的生物效应，结果显示，苯福林在两种血管收缩实验中表现解离常数Ｋａｐｐ值无显著性差异，而甲氧明和羟甲唑啉的Ｋａｐｐ值则在肾动脉显著小于主动脉。上述结果提示去甲肾上腺素，苯福林和Ａ５７２１９对α１－ＡＲ的两种亚型没有选择性，而甲氧明与羟甲唑啉对α１Ａ－ＡＲ亚型的亲和性明显大于α１Ｂ－ＡＲ亚型。     

大鼠α1肾上腺素受体及其亚型影响β肾上腺素受体介…

在大鼠心脏上同时激动α１肾上腺素受体（α１－ＡＲ）与β－肾上腺素受体（β－ＡＲ），较单独激动β－ＡＲ时产生的ｃＡＭＰ明显减少，α１Ａ－ＡＲ亚型抑制，而α１Ｂ－ＡＲ亚型增强β－ＡＲ刺激ｃＡＭＰ生成的作用。但α１－ＡＲ及其亚型激动不影响ｆｏｒｓｋｏｌｉｎ引起的ｃＡＭＰ生成，亦不影响β－ＡＲ与〔＾１２５Ｉ〕吲哚洛尔的最大结合容量和解离常数。苯福林激动α１－ＡＲ对三磷酸鸟苷使丙肾上腺素与〔＾１２５Ｉ〕ＫＸ     

Characterization of an alpha 1D-adrenoceptor mediating the contractile response of rat aorta to noradrenaline.

1. The affinities of a number of alpha 1-adrenoceptor antagonists were determined by displacement of [3H]-prazosin binding from cloned human alpha 1A-adrenoceptors (previously designated cloned alpha 1c subtype), alpha 1B alpha 1D and rat alpha 1D-adrenoceptors, stably expressed in rat-1 fibroblasts. Functional affinity estimates for these compounds were also determined from noradrenaline-mediated contractions of rat aorta. 2. BMY 7378 displayed high affinity for cloned human alpha 1D-adrenoceptors (pKi = 8.2 +/- 0.10) and was selective over alpha 1A (pKi = 6.2 +/- 0.10) and alpha 1B subtypes (6.7 +/- 0.11). WB 4101, benoxathian and phentolamine displayed high affinity for alpha 1A and alpha 1D adrenoceptors compared to the alpha 1B subtype. Spiperone displayed high affinity and selectivity for alpha 1B adrenoceptors (pKi 8.8 +/- 0.16). 5-Methyl-urapidil was selective for cloned alpha 1A adrenoceptors. 3. Comparative binding affinities (pKi) for compounds at cloned human and rat1D adrenoceptors were almost identical (r = 0.99, slope = 1.08). 4. Prazosin, doxazosin and 5-methyl-urapidil were potent, competitive antagonists of noradrenaline-mediated contractions of rat aorta (pA2 values of 9.8, 8.8 and 7.8 respectively). The selective alpha 1D antagonist BMY 7378 was also a potent antagonist on rat aorta (pKB = 8.3 +/- 0.1) but the interaction of this compound was not consistent with competitive antagonism at a single population of receptors. 5. Functional affinities for compounds determined against noradrenaline-mediated contractions of rat aorta correlated well with binding affinities at cloned alpha 1D-adrenoceptors (r = 0.96), but not with alpha 1A (r = 0.61) or alpha 1B (r = 0.46) subtypes.(ABSTRACT TRUNCATED AT 250 WORDS)     

The alpha-adrenoceptor antagonist, zolertine, inhibits alpha1D- and alpha1A-adrenoceptor-mediated vasoconstriction in vitro

1. The antagonist effect of zolertine (4-phenyl-1-[2-(5-tetrazolyl)ethyl]piperazine trihydrochloride), on vascular contraction elicited by noradrenaline in aorta, carotid (alpha1D-adrenoceptors), mesenteric (alpha1A/D-adrenoceptors) and caudal arteries (alpha1A-adrenoceptors) from Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats and rabbit aorta (alpha1B-adrenoceptors), was investigated in endothelium-denuded arterial rings. 2. The selective alpha1D-adrenoceptor agonist, noradrenaline, elicited concentration-dependent contractions in all arterial rings from both species. Noradrenaline selectivity was: carotid = aorta > mesenteric = rabbit aorta > caudal arteries. 3. The contractile responses induced by noradrenaline were competitively antagonized by zolertine in rat carotid and aorta arteries, yielding pA2 values of WKY, 7.48 +/- 0.18; SHR, 7.43 +/- 0.13 and WKY, 7.57 +/- 0.24; SHR, 7.40 +/- 0.08, respectively. Zolertine was a non-competitive antagonist in some blood vessels as Schild plot slopes were lower than unity. The pKb estimates for zolertine were WKY, 6.98 +/- 0.16; SHR, 6.81 +/- 0.18 in the mesenteric artery, WKY, 5.73 +/- 0.11; SHR, 5.87 +/- 0.25 in the caudal artery and 6.65 +/- 0.09 in rabbit aorta. 4. Competition binding experiments using the alpha1-adrenoceptor antagonist [3H]prazosin showed a zolertine pKi of 6.81 +/- 0.02 in rat liver (alpha1B-adrenoceptors) and 6.35 +/- 0.04 in rabbit liver (alpha1A-adrenoceptors) membranes. 5. Zolertine showed higher affinity for alpha1D-adrenoceptors compared to alpha1A-adrenoceptors, while it had an intermediate affinity for alpha1B-adrenoceptors. The ability of the alpha1-adrenoceptor antagonist zolertine to block alpha1D-adrenoceptor-mediated constriction in different vessels of WKY and SHR rats may explain its antihypertensive efficacy despite its low order of potency.     

The adrenoceptor agonist, SDZ NVI 085, discriminates between alpha 1A- and alpha 1B-adrenoceptor subtypes in vas deferens, kidney and aorta of the rat.

The potency of the alpha 1-adrenoceptor agonist (-)-(4aR, 10aR)-3,4,4a,5,10,10a-hexahydro-6-methoxy-4-methyl-9-methylthio-2H -naphth [2,3-b]-1,4-oxazine (SDZ NVI 085) was investigated both in isolated vas deferens and perfused kidney of the rat, two tissues with alpha 1A-adrenoceptor subtype characteristics, and in the rat thoracic aorta, in which the contribution of different alpha 1-adrenoceptor subtypes mediating contraction is controversial. In vas deferens and kidney, SDZ NVI 085 evoked smooth muscle contraction and vascular constriction and was of similar potency to L-phenylephrine. Contractions of vas deferens in response to (-)-noradrenaline and SDZ NVI 085 were resistant to chloroethylclonidine treatment (3 x 10(-5) M), sensitive to (+/-)-isradipine (10(-8) M) and competitively antagonized by 5-methyl-urapidil (pA2 = 9.04 and 8.82, respectively). The potencies of a number of alpha 1A-/alpha 1B-adrenoceptor-discriminating antagonists to reverse renal vasoconstriction due to either (-)-noradrenaline or SDZ NVI 085, and their affinities in vas deferens correlated significantly with their pKi values at alpha 1A binding sites in rat cortex. In rat aorta, SDZ NVI 085 up to 5 x 10(-4) M failed to evoke contraction. The affinities of subtype-selective antagonists determined in aorta correlated significantly with the pKi values at alpha 1B binding sites but differed from pKi values at alpha 1A sites in rat cortex. Thus, the contractile alpha 1-adrenoceptor in rat aorta can be best characterized as B subtype. SDZ NVI 085 might be a selective alpha 1A-adrenoceptor agonist and thus be used as a new tool either to detect (rat vas deferens and kidney) or exclude (rat aorta) a contribution of alpha 1A-adrenoceptors functionally involved in smooth muscle contraction.     

A comparative study of postsynaptic α2-adrenoceptors of the dog mesenteric and rat femoral veins

The aim of the present study was to compare the subtype of postjunctional alpha2-adrenoceptors of canine mesenteric and rat femoral veins. To check whether the presence of alpha1-adrenoceptors in both tissues might interfere with alpha2-adrenoceptor-mediated effects, the experiments were carried out under two experimental conditions: without and with alpha1-adrenoceptor blockade. The selective and irreversible alpha1-adrenoceptor antagonist phenoxybenzamine (30 nM) was used to eliminate alpha1-adrenoceptors. The pA2 values for the antagonism exerted by eight alpha-adrenoceptor antagonists (rauwolscine, yohimbine, RX821002, WB4101, idazoxan, phentolamine, spiroxatrine and prazosin) against the highly selective alpha2-adrenoceptor agonist UK-14,304 were determined under these two experimental conditions and correlated with pKi values of the same antagonists at cloned human alpha2A-, alpha2B- and alpha2C-adrenoceptors expressed in Chinese hamster lung cells and at the alpha2D-adrenoceptors in the rat submaxillary gland or the bovine pineal gland. In most of the experiments carried out in the canine mesenteric vein, the concentration-response curves for UK-14,304 were biphasic; the first phase was antagonized by low concentrations (2-50 nM) of the antagonists used except prazosin, while the second one was antagonized by 30 nM of either prazosin or phenoxybenzamine. In the rat femoral vein, the concentration-response curves to UK-14,304 were monophasic. In either tissue, the pA2 values obtained in untreated preparations and in preparations pretreated with phenoxybenzamine were not significantly different, showing that effects resulting from the activation of alpha1-adrenoceptors can be avoided simply by using low concentrations of the highly selective alpha2-adrenoceptor agonist UK-14,304. The correlation between pA2 and pKi values showed that, while in the canine mesenteric vein the postjunctional alpha2-adrenoceptors resemble alpha2A-adrenoceptors more closely, in the rat femoral vein they are more closely related to alpha2D-adrenoceptors. In either species, therefore, they belong to the genetic alpha2A/D type of alpha2-adrenoceptor.     

Analysis of alpha1-adrenoceptor subtypes in rabbit aorta and arteries: regional difference and co-existence.

This study was done to determine the alpha1-adrenoceptor subtypes and to characterize the functional role of alpha1D-adrenoceptors in the following rabbit arteries: thoracic and abdominal aorta, mesenteric, renal and iliac arteries. In all arteries, selective alpha1D-adrenoceptor antagonist BMY 7378 (8-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-8-azaspirol(4,5) decane-7,9-dione dihydrochloride) dose dependently shifted the concentration-response curves for norepinephrine to the right. Schild plots of the results obtained from the inhibition by BMY 7378 for norepinephrine yielded a straight line with a slope of unity in thoracic (pA2 6.54+/-0.02) and abdominal (pA2 6.73+/-0.03) aorta. Slopes of Schild plots obtained from the inhibition by BMY 7378 for norepinephrine were significantly different from unity in mesenteric, renal and iliac arteries. Slopes of Schild plots for BMY 7378 were not different from unity in chloroethylclonidine-treated thoracic (pA2 6.49+/-0.14) and abdominal (pA2 6.61+/-0.11) aorta. Slopes of Schild plots for BMY 7378 were significantly different from unity in chloroethylclonidine-treated mesenteric, renal and iliac arteries. On the other hand, in Ca2+-free physiological saline solution (Ca2+-free PSS) slopes obtained from Schild plots for BMY 7378 were not different from unity in thoracic (pA2 6.41+/-0.09) and abdominal (pA2 6.28+/-0.07) aorta and mesenteric (pA2 6.55+/-0.06), renal (pA2 6.24+/-0.10) and iliac (pA2 6.64+/-0.13) arteries. BMY 7378 inhibited [3H]prazosin binding to thoracic (pKi 6.44+/-0.08) and abdominal (pKi 6.59+/-0.02) aorta with low potency, and mesenteric (pKi High 8.66+/-0.28, pKi Low 6.34+/-0.14), renal (pKi High 8.71+/-0.33, pKi Low 6.45+/-0.03) and iliac artery (pKi High 8.60+/-0.24, pKi Low 6.56+/-0.13). These results suggest that alpha1D-adrenoceptors play a significant role for contractile responses in renal and iliac artery, but play virtually no role in thoracic and abdominal aorta and that an alpha1-adrenoceptor subtype, which is pharmacologically distinguishable from the alpha1A-, alpha1B- and alpha1D-adrenoceptor subtype, may co-exist in mesenteric artery.     

Evaluation of the pharmacological selectivity profile of alpha 1 adrenoceptor antagonists at prostatic alpha 1 adrenoceptors: binding, functional and in vivo studies.

1. The profile of a range of alpha 1 adrenoceptor antagonists was determined in vitro against cloned human alpha 1A, alpha 1B and alpha 1D adrenoceptors and against noradrenaline-mediated contractions of rat aorta and human prostate. The in vivo profile of compounds was determined in an anaesthetized dog model which allowed the simultaneous assessment of antagonist potency against phenylephrine-mediated increases in blood pressure and prostatic pressure. 2. The quinazoline antagonists, prazosin, doxazosin and alfuzosin displayed high affinity but were non selective for the three cloned human alpha 1 adrenoceptors. Indoramin and SNAP 1069 showed selectivity for alpha 1A and alpha 1B adrenoceptors relative to the alpha 1D subtype. Rec 15/2739, WB 4101, SL 89,0591, (+)- and (-)- tamsulosin showed selectivity for alpha 1A and alpha 1D adrenoceptors relative to the alpha 1B subtype. RS 17053 showed high affinity and selectivity for alpha 1A adrenoceptors (pKi 8.6) relative to alpha 1B (pKi = 7.3) and alpha 1D (pKi = 7.1) subtypes. 3. (+)-Tamsulosin, (-)-tamsulosin, SL 89,0591, Rec 15/2739, SNAP 1069 and RS 17053 appeared to act as competitive antagonists of noradrenaline-mediated contractions of rat aorta yielding pA2 affinity estimates which were similar to binding affinities at cloned human alpha 1D adrenoceptors. The following rank order was obtained: prazosin = (-)-tamsulosin > doxazosin > SL 89,0591 = (+)-tamsulosin > Rec 15/2739 > RS 17053 = SNAP 1069. 4. (-)-Tamsulosin was a very potent, insurmountable antagonist of noradrenaline-mediated contractions of human prostate, yielding an approximate pA2 estimate of 9.8 at 1 nM. The corresponding (+)-enantiomer was 30 fold weaker. SL 89,0591, SNAP 1069 and Rec 15/2739 yielded pA2 estimates which compared well with their alpha 1A binding affinities. The affinity estimate for prazosin on human prostate was lower than the corresponding binding affinity determined at alpha 1A adrenoceptors and RS 17053 was a very weak antagonist on human prostate (pA2 = 6.0) relative to the high affinity (pKi = 8.6) determined at cloned human alpha 1A adrenoceptors. 5. In the anaesthetized dog, in vivo pseudo "pA2' values showed that doxazosin, (+)- and (-)-tamsulosin inhibited phenylephrine-induced increases in prostatic and blood pressure with similar affinity, implying that these agents show little or no selectivity for prostatic responses in this model. SL 89,0591 and SNAP 1069 were moderately selective (3 and 6 fold respectively) for prostatic pressure relative to blood pressure. Rec 15/2739 was a more potent antagonist of phenylephrine-mediated increases in prostatic pressure ("pA2' = 8.74) compared to blood pressure ("pA2' = 7.51). 6. Data in this study suggest that the alpha 1 adrenoceptor mediating noradrenaline-induced contractions of human prostate, whilst having some of the characteristics of an alpha 1A adrenoceptor, cannot be satisfactorily aligned with cloned alpha 1A, alpha 1B or alpha 1D adrenoceptors. In addition, studies in the anaesthetized dog have shown that agents having high affinity and selectivity for prostatic alpha 1 adrenoceptors, particularly over the alpha 1D subtype, appear to inhibit phenylephrine-induced increases in prostatic pressure selectively compared to blood pressure.     

Analysis of alpha 1L-adrenoceptor pharmacology in rat small mesenteric artery.

1. To illuminate the controversy on alpha 1A- or alpha 1L-adrenoceptor involvement in noradrenaline-mediated contractions of rat small mesenteric artery (SMA), we have studied the effects of subtype-selective alpha 1-adrenoceptor agonists and antagonists under different experimental conditions. 2. The agonist potency order in rat SMA was: A61603 > SKF89748-A > cirazoline > noradrenaline > ST-587 > methoxamine. Prazosin antagonized all agonists with a low potency (pA2: 8.29-8.80) indicating the involvement of alpha 1L-rather than alpha 1A-adrenoceptors. 3. The putative alpha 1L-adrenoceptor antagonist JTH-601, but not the alpha 1B-adrenoceptor antagonist chloroethylclonidine (10 microM) antagonized noradrenaline-induced contractions of SMA. The potency of the selective alpha 1D-adrenoceptor antagonist BMY 7378 against noradrenaline (pA2 = 6.16 +/- 0.13) and of the selective alpha 1A-adrenoceptor antagonist RS-17053 against noradrenaline (pKB = 8.35 +/- 0.10) and against the selective alpha 1A-adrenoceptor agonist A-61603 (pKB = 8.40 +/- 0.09) were too low to account for alpha 1D- and alpha 1A-adrenoceptor involvement. 4. The potency of RS-17053 (pKB/pA2's = 7.72-8.46) was not affected by lowering temperature, changing experimental protocol or inducing myogenic tone via KCl or U46619. 5. Selective protection of a putative alpha 1A-adrenoceptor population against the irreversible action of phenoxybenzamine also failed to increase the potency of RS-17053 (pA2 = 8.25 +/- 0.06 against A61603). 6. Combined concentration-ratio analysis demonstrated that tamsulosin, which does not discriminate between alpha 1A- and alpha 1L-adrenoceptors, and RS-17053 competed for binding at the same site in the SMA. 7. In summary, data obtained in our experiments in rat SMA indicate that the alpha 1-adrenoceptor mediating noradrenaline-induced contraction displays a distinct alpha 1L-adrenoceptor pharmacology. This study does not provide evidence for the hypothesis that alpha 1L-adrenoceptors represent an affinity state of the alpha 1A-adrenoceptor in functional assays. Furthermore, there is no co-existing alpha 1A-adrenoceptor in the SMA.     

Vasodilatation elicited by 5-HT1A receptor agonists in constant-pressure-perfused rat kidney is mediated by blockade of alpha 1A-adrenoceptors.

The vasodilator mechanism of the putative serotonin1A (5-HT) receptor agonists, urapidil, 5-methyl-urapidil, ipsapirone, flesinoxan and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) was investigated in constant-pressure perfused rat kidneys. The compounds (10(-12)-10(-7) mol bolus injection) neither enhanced basal flow nor evoked vasodilatation in kidneys preconstricted by 27 mM KCl, 1.5 mM BaCl2 or 10(-6) M prostaglandin (PG)F2 alpha, but evoked a dose-dependent, reversible and spiroxatrine-resistant increase in vasodilatation of organs preconstricted by 6 x 10(-7) M noradrenaline. 5-Carboxamidotryptamine and sumatriptan did not reverse the vasoconstriction induced by all stimuli or that induced by noradrenaline in the presence of 5-HT2 plus 5-HT3 receptor blockade. No correlation for the vasorelaxant drugs was found between their -log ED50 in rat kidney and pKi values at 5-HT1A binding sites in pig cortex as determined in radioligand experiments. The relaxation in rat kidney induced by 5-HT1A receptor agonists and alpha 1A-adrenoceptor-selective antagonists (WB 4101 and (+)-niguldipine) was significantly correlated with pKi values at alpha 1A binding sites in rat cortex and the pA2 values derived from contraction studies for competitive antagonism at alpha 1-adrenoceptors in prostatic portions of the rat vas deferens, but differed from pKi values for alpha 1B binding sites in rat cortex. Thus, the vasodilator effect of the 5-HT1A receptor agonists urapidil, 5-methyl-urapidil, ipsapirone, flesinoxan and 8-OH-DPAT in the noradrenaline-perfused rat kidney appears to be mediated by their concomitant alpha 1A-adrenoceptor blockade. No evidence for a vasodilator effect mediated through 5-HT1A receptors was found under our experimental conditions.     

Characterization of alpha 1-adrenoceptors mediating vasoconstriction to noradrenaline and nerve stimulation in the isolated perfused mesentery of rat.

1. The objective of this study was to investigate the alpha 1-adrenoceptor subtype(s) mediating vasoconstrictor responses to perfused and neuronally-released noradrenaline (NA) in the isolated perfused mesentery preparation of rat. 2. Isolated mesenteric preparations (with gut attached) from male Sprague Dawley rats (250-300g) were perfused via the superior mesenteric artery with oxygenated Krebs solution at approximately 6 ml min-1. The effects of antagonists on vasoconstrictor responses to either perfused (+/-)-NA or periarterial nerve stimulation (70 V, 2 ms pulse width, 10 s train) were determined. 3. Vasoconstrictor responses to perfused NA were antagonized by prazosin (pA2 = 9.3 +/- 0.1), WB4101 (pA2 = 9.6 +/- 0.1), 5-methyl urapidil (5-MU: pA2 = 9.0 +/- 0.1), (+)-niguldipine (insurmountable) and spiperone (pA2 = 7.7 +/- 0.1). The insurmountable nature of the antagonism by (+)-niguldipine (0.1 nM) was greatly reduced by co-perfusion with prazosin (10 nM). Chloroethylclonidine (CEC: 100 microM for 20 min, followed by 40 min washout) caused an approximate twofold increase in the EC50 for (+/-)-NA and reduced the maximum response by approximately 25%. Pre-treatment of tissues with CEC (100 microM as above) did not significantly alter affinity estimates for prazosin (pA2 = 9.2 +/- 0.1), WB4101 (pA2 = 9.3 +/- 0.1) or 5-MU (pA2 = 8.7 +/- 0.2). Vasoconstrictor responses to periarterial nerve stimulation were antagonized by WB4101 > 5-MU > prazosin >> spiperone. CEC (100 microM as above) reduced nerve-stimulated responses by approximately 50%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Buspirone functionally discriminates tissues endowed with alpha1-adrenoceptor subtypes A, B, D and L.

The affinity for functional alpha1-adrenoceptor subtypes of buspirone in comparison with its close structural analogs and selective alpha1D-adrenoceptor antagonists, BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]dec ane-7,9-dione) and MDL 73005EF (8-[2-(1,4-benzodioxan-2-ylmethylamino)ethyl]-8-azaspiro+ ++[4.5]decane-7,9-dione), was determined, namely at subtype A in rat vas deferens and perfused kidney, at subtype B in guinea-pig and mouse spleen, at subtype L in rabbit spleen, and at subtype D in rat aorta and pulmonary artery against noradrenaline-evoked contractions. BMY 7378 and MDL 73005EF were confirmed as 30- and 20-fold selective antagonists, respectively, for alpha1D- over both alpha1A- and alpha1B-adrenoceptors. Buspirone was a weak antagonist without intrinsic activity at alpha1A-adrenoceptors in rat vas deferens (pA2 = 6.12), at alpha1B-adrenoceptors in guinea-pig and mouse spleen (pA2 = 5.54 and 5.59) and at alpha1L-adrenoceptors in rabbit spleen (pA2 = 4.99), but caused partial vasoconstriction in rat kidney that was attenuable by the subtype D-selective adrenoceptor antagonist BMY 7378, but hardly by the subtype A-selective adrenoceptor antagonist B8805-033 ((+/-)-1,3,5-trimethyl-6-[[3-[4-((2,3-dihydro-2-hydroxymethyl)-1,4-be nzodioxin-5-yl)-1-piperazinyl]propyl]amino]-2,4(1H,3H)-pyrimidinedion e), confirming the additional presence of alpha1D-adrenoceptors mediating rat renal vasoconstriction. Buspirone behaved as a partial agonist at alpha1D-adrenoceptors in rat aorta (pD2 = 6.77, intrinsic activity (i.a.)= 0.40) and pulmonary artery (pD2 = 7.16, i.a. = 0.59). With buspirone as agonist in these tissues, the pA2 values of subtype-discriminating antagonists were consistent with their alpha1D-adrenoceptor affinity determined in rat aorta against noradrenaline and with published binding data on cloned alpha1d-adrenoceptors. The results provide pharmacological evidence that (1) in functional preparations for the A subtype, like rat vas deferens and perfused kidney, for the B subtype, like guinea-pig and mouse spleen, and for the L subtype, like rabbit spleen, buspirone is a weak antagonist without intrinsic activity, but (2) behaves as a partial agonist in rat aorta and pulmonary artery as models for the D subtype and (3) detects an additional vasoconstrictor alpha1D-adrenoceptor in rat kidney. Buspirone, like its close analogs BMY 7378 and MDL 73005EF, thus might also be a useful tool for functionally discriminating alpha1D- from alpha1A-, alpha1B- and alpha1L-adrenoceptors in various tissues.