Tamsulosin potently and selectively antagonizes human recombinant α(1A/1D)-adrenoceptors: slow dissociation from the α(1A)-adrenoceptor may account for selectivity for α(1A)-adrenoceptor over α(1B)-adrenoceptor subtype

We determined the binding affinity of tamsulosin, a selective α(1)-adrenoceptor antagonist, for human α(1)-adrenoceptor subtypes in comparison with those of other α(1)-adrenoceptor antagonists including silodosin, prazosin, 5-methylurapidil, terazosin, alfuzosin, nafopidil, urapidil and BMY7378. The association and dissociation kinetics of [(3)H]tamsulosin for recombinant human α(1)-adrenoceptor subtypes were compared with those of [(3)H]prazosin. Tamsulosin competitively inhibited [(3)H]prazosin binding to human α(1A)-, α(1B)- and α(1D)-adrenoceptors (pK(i) values were 10.38, 9.33, 9.85) indicating 11 and 3.4-fold higher affinities for human α(1A)-adrenoceptor than those for α(1B)- and α(1D)-adrenoceptors, respectively. The affinity of tamsulosin for the human α(1A)-adrenoceptor was, respectively, 5, 9.9, 38, 120, 280, 400, 1200 and 10000 fold higher than those of silodosin, prazosin, 5-methylurapidil, terazosin, alfuzosin, naftopidil, urapidil and BMY7378, respectively. [(3)H]Tamsulosin dissociated from the α(1A)-adrenoceptor slower than from the α(1B)- and α(1D)-adrenoceptors (α(1B)>α(1D)>α(1A)). Moreover, [(3)H]tamsulosin dissociated slower than [(3)H]prazosin from the α(1A)-adrenoceptor and faster from the α(1B)- and α(1D)-adrenoceptors. In conclusion, tamsulosin potently and selectively antagonized α(1A/1D)-adrenoceptor ligand binding, and slowly dissociated from the α(1A)-adrenoceptor subtype.     

α(1D)-Adrenoceptor regulates the vasopressor action of α(1A)-adrenoceptor in mesenteric vascular bed of α(1D)-adrenoceptor knockout mice

1 The pressor action of the α(1A)-adrenoceptor (α(1A)-AR) agonist A61603 (N-[5-(4,5-dihydro-1H-imidazol-2-yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl] methanesulfonamide) and the α(1)-ARs agonist phenylephrine and their blockade by selective α(1)-ARs antagonists in the isolated mesenteric vascular bed of wild-type (WT) mice and α(1D)-AR knockout (KO α(1D)-AR) mice were evaluated. 2 The apparent potency of A61603 to increase the perfusion pressure in the mesenteric vascular bed of WT and KO α(1D)-AR mice is 86 and 138 times the affinity of phenylephrine, respectively. 3 A61603 also enhanced the perfusion pressure by ≈1.7 fold in the mesenteric vascular bed of WT mice compared with KO α(1D)-AR mice. 4 Because of its high affinity, low concentrations of the α(1A)-AR selective antagonist RS100329 (5-methyl-3-[3-[4-[2-(2,2,2,-trifluoroethoxy) phenyl]-1-piperazinyl] propyl]-2,4-(1H)-pyrimidinedione) shifted the agonist concentration-response curves to the right in the mesenteric vascular bed of WT and KO α(1D)-AR mice. 5 The α(1D)-AR selective antagonist BMY7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5] decane-7,9-dione) did not modify the A61603 or the phenylephrine-induced pressor effect. 6 The α(1B/D)-ARs alkylating antagonist chloroethylclonidine (CEC) shifted the agonist concentration-response curves to the right and decreased the maximum phenylephrine-induced vascular contraction in KO α(1D)-AR mice when compared to WT mice; however, CEC only slightly modified the contraction induced by A61603. 7 The results indicate that the isolated mesenteric vascular bed of WT and KO α(1D)-AR mice expresses α(1A)-AR, that the pressor action of α(1A)-AR is up-regulated for α(1D)-AR in WT mice and suggest an important role of α(1B)-AR in the vascular pressure evoked by phenylephrine in KO α(1D)-AR mice.     

Alkaloids and flavonoids as α(1)-adrenergic receptor antagonists

Since the subtypes of α(1)-adrenergic receptor have been thoroughly determined, to date medicinal chemists raise their deliberation on how to conceive selective α(1)-adrenergic receptor antagonist with the minimal side effects. It needs to be well recognized that natural products can exist as a significant source of drug leads, thus portraying a consequential capacity in drug design and development. The current review article would like to present a comprehensive survey on natural products, mainly including alkaloids and flavonoids, which exhibit α(1)-adrenergic receptor antagonistic activities.     

Phenotype pharmacology of lower urinary tract α(1)-adrenoceptors

α(1)-Adrenoceptors are involved in numerous physiological functions, including micturition. However, the pharmacological profile of the α(1)-adrenoceptor subtypes remains controversial. Here, we review the literature regarding α(1)-adrenoceptors in the lower urinary tract from the standpoint of α(1L) phenotype pharmacology. Among three α(1)-adrenoceptor subtypes (α(1A), α(1B) and α(1D)), α(1a)-adrenoceptor mRNA is the most abundantly transcribed in the prostate, urethra and bladder neck of many species, including humans. In prostate homogenates or membrane preparations, α(1A)-adrenoceptors with high affinity for prazosin have been detected as radioligand binding sites. Functional α(1)-adrenoceptors in the prostate, urethra and bladder neck have low affinity for prazosin, suggesting the presence of an atypical α(1)-adrenoceptor phenotype (designated as α(1L)). The α(1L)-adrenoceptor occurs as a distinct binding entity from the α(1A)-adrenoceptor in intact segments of variety of tissues including prostate. Both the α(1L)- and α(1A)-adrenoceptors are specifically absent from Adra1A (α(1a)) gene-knockout mice. Transfection of α(1a)-adrenoceptor cDNA predominantly expresses α(1A)-phenotype in several cultured cell lines. However, in CHO cells, such transfection expresses α(1L)- and α(1A)-phenotypes. Under intact cell conditions, the α(1L)-phenotype is predominant when co-expressed with the receptor interacting protein, CRELD1α. In summary, recent pharmacological studies reveal that two distinct α(1)-adrenoceptor phenotypes (α(1A) and α(1L)) originate from a single Adra1A (α(1a)-adrenoceptor) gene, but adrenergic contractions in the lower urinary tract are predominantly mediated via the α(1L)-adrenoceptor. From the standpoint of phenotype pharmacology, it is likely that phenotype-based subtypes such as the α(1L)-adrenoceptor will become new targets for drug development and pharmacotherapy.     

Quantification of functional selectivity at the human α(1A)-adrenoceptor

Although G protein-coupled receptors are often categorized in terms of their primary coupling to a given type of Gα protein subunit, it is now well established that many show promiscuous coupling and activate multiple signaling pathways. Furthermore, some agonists selectively activate signaling pathways by promoting interaction between distinct receptor conformational states and particular Gα subunits or alternative signaling proteins. We have tested the capacity of agonists to stimulate Ca(2+) release, cAMP accumulation, and changes in extracellular acidification rate (ECAR) at the human α(1A)-adrenoceptor. Signaling bias factors were determined by novel application of an operational model of agonism and compared with the reference endogenous agonist norepinephrine; values significantly different from 1.0 indicated an agonist that promoted receptor conformations distinct from that favored by norepinephrine. Oxymetazoline was a full agonist for ECAR and a partial agonist for Ca(2+) release (bias factor 8.2) but failed to stimulate cAMP production. Phenylephrine showed substantial bias toward ECAR versus Ca(2+) release or cAMP accumulation (bias factors 21 and 33, respectively) but did not display bias between Ca(2+) and cAMP pathways. Cirazoline and N-[5-(4,5-dihydro-1H-imidazol-2-yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl]methanesulfonamide (A61603) displayed bias toward cAMP relative to Ca(2+) release (bias factors of 7.4 and 8.6). It is noteworthy that epinephrine, a second endogenous adrenoceptor agonist, did not display bias relative to norepinephrine. Our finding that phenylephrine displayed significant signaling bias, despite being highly similar in structure to epinephrine, indicates that subtle differences in agonist-receptor interaction can affect conformational changes in cytoplasmic domains and thereby modulate the repertoire of effector proteins that are activated.     

Pregabalin is a potent and selective ligand for α(2)δ-1 and α(2)δ-2 calcium channel subunits

Pregabalin, a synthetic branched chain γ-amino acid with anticonvulsant, anxiolytic, and analgesic activities, has been shown to bind with high affinity to the voltage-gated calcium channel α(2)δ subunit. Given the broad therapeutic utility of pregabalin, a series of experiments was undertaken to determine the potency, selectivity, and specificity of pregabalin's receptor-binding profile at α(2)δ-1 and α(2)δ-2 subunits of voltage-gated calcium channels along with 38 widely studied receptors and channels. Receptor autoradiography was used to assess regional-binding density of pregabalin throughout the rat spinal cord and brain. In addition, a series of studies using in vivo electrophysiological recordings of γ-aminobutyric acid (GABA)(A)- and GABA(B)-evoked currents was undertaken to determine the interaction of pregabalin with GABAergic receptor subtypes. Together, the results of these studies demonstrate potent and selective binding of pregabalin to α(2)δ-1 and α(2)δ-2 subunits in native and recombinant human and porcine systems. Pregabalin did not interact with any of the 38 receptors and ion channels evaluated, and a variety of central nervous system (CNS)-targeted therapeutic drugs did not show activity at the α(2)δ subunits of voltage-gated calcium channels. Receptor autoradiography demonstrated extensive [(3)H]-pregabalin binding throughout the CNS, with high-level binding in the cortex, hippocampus, cerebellum, dorsal horn of the spinal cord, and amygdala. Finally, receptor-binding and electrophysiological techniques failed to show evidence of an interaction between pregabalin and GABA(A) or GABA(B) receptors. These studies suggest that the clinical effects of pregabalin are likely due to direct and selective interactions with α(2)δ-1 and α(2)δ-2 subunits of voltage-gated calcium channels.     

1H-Nuclear Magnetic Resonance (NMR) Studies on the Inclusion Complex of Prostaglandin El (PGE1 with α-Cyclodextrin

Prostaglandin E_l is currently marketed as a freeze-dried injectable inclusion complex with -cyclodextrin for the treatment of peripheral arterial diseases. -Cyclodextrin is used as a stabilizing agent and to improve the dissolution characteristics of prostaglandin E_l. Upon dilution with the infusion medium, the inclusion complex dissociates almost completely as shown by NMR chemical shift measurements of the complexed and uncomplexed prostaglandin E₁ Nuclear Overhauser effect (NOE) measurements of the interacting atoms of -cyclodextrin and prostaglandin E_l provide insight into the structure of the complex.     

Isolation and characterization of α-(1→6)-glucans from Cistanche deserticola

Three unique polysaccharides (1–3) have been obtained from the 0.5 M NaOH extract of the stem of Cistanche deserticola Y. C. Ma. The results of methylation analysis, partial acid hydrolysis, ¹³C, ¹H NMR, ¹H–¹H COSY, HMQC and HMBC spectroscopic analyses indicate that they are all composed of glucose, having a backbone of α-(1 → 6)-glucan, and have different molecular weights. Their structures differ from that of linear starch.     

Agonist pharmacology at recombinant α1A- and α1L-adrenoceptors and in lower urinary tract α1-adrenoceptors

BACKGROUND AND PURPOSE

Two distinct α₁-adrenoceptor phenotypes (α_1A and α_1L) have recently been demonstrated to originate from a single α_1A-adrenoceptor gene. Here, we examined the agonist profiles of recombinant α_1A and α_1L phenotypes and of lower urinary tract (LUT) α₁-adrenoceptors.

EXPERIMENTAL APPROACH

A series of drugs (A61603, Ro 115–1240, NS-49, MK017 and ESR1150) originally developed for stress urinary incontinence (SUI) therapy were used to stimulate recombinant α_1A- and α_1L-adrenoceptor phenotypes, and their potencies and intrinsic activity estimated from Ca²⁺ responses. Agonist-induced contractions were also examined in LUT tissues of rats and humans and in human mesenteric artery and rat tail artery.

KEY RESULTS

All the drugs were potent agonists of the α_1A-adrenoceptor compared with the α_1L-adrenoceptor phenotype. Among them, Ro 115–1240 was shown to be an α_1A-specific partial agonist that produced partial contractions through α_1A-adrenoceptors in rat prostate and tail artery, but not in the other LUT tissues and human mesenteric artery. In contrast, P-come 102 showed full agonist activity at α_1A- and α_1L-adrenoceptors, but was less selective than noradrenaline for α_1A-adrenoceptors. Like noradrenaline, P-come 102 was highly potent at inducing contractions in all of the LUT tissues tested. However, the potency and intrinsic activity of P-come 102 were significantly lower than those of noradrenaline in human mesenteric artery.

CONCLUSIONS AND IMPLICATIONS

The α_1A- and α_1L-adrenoceptor phenotypes and LUT α₁-adrenoceptors were demonstrated to have distinct agonist profiles. As adrenergic contractions in LUT are predominantly mediated through α_1L-adrenoceptors, the development of α_1L-selective agonists may provide clinically useful drugs for SUI therapy.     

实例(1)

前置胎盘是中晚期妊娠阴道出血的最常见原因,如不能早期发现和及时治疗,常引致大量出血而危及生命。超声检查是目前胎盘定位的首选方法。某作者通过超声诊断确定完全性前置胎盘6例,部分性前置胎盘8例,边缘性前置胎盘5例,低置胎盘10例,共计29例。经孕妇分娩后证实为前置胎盘者28例,超声诊断前置胎盘的符合率为96.6％;1例为先兆流产,超声诊断前置胎盘的误诊率为3.4％。     

Role of α1- and α2-GABA(A) receptors in mediating the respiratory changes associated with benzodiazepine sedation

BACKGROUND AND PURPOSE

The molecular substrates underlying the respiratory changes associated with benzodiazepine sedation are unknown. We examined the effects of different doses of diazepam and alprazolam on resting breathing in wild-type (WT) mice and clarified the contribution of α1- and α2-GABA_A receptors, which mediate the sedative and muscle relaxant action of diazepam, respectively, to these drug effects using point-mutated mice possessing either α1H101R- or α2H101R-GABA_A receptors insensitive to benzodiazepine.

EXPERIMENTAL APPROACH

Room air breathing was monitored using whole-body plethysmography. Different groups of WT mice were injected i.p. with diazepam (1–100 mg·kg⁻¹), alprazolam (0.3, 1 or 3 mg·kg⁻¹) or vehicle. α1H101R and α2H101R mice received 1 or 10 mg·kg⁻¹ diazepam or 0.3 or 3 mg·kg⁻¹ alprazolam. Respiratory frequency, tidal volume, time of expiration and time of inspiration before and 20 min after drug injection were analysed.

KEY RESULTS

Diazepam (10 mg·kg⁻¹) decreased the time of expiration, thereby increasing the resting respiratory frequency, in WT and α2H101R mice, but not in α1H101R mice. The time of inspiration was shortened in WT and α1H101R mice, but not in α2H101R mice. Alprazolam (1–3 mg·kg⁻¹) stimulated the respiratory frequency by shortening expiration and inspiration duration in WT mice. This tachypnoeic effect was partially conserved in α1H101R mice while absent in α2H101R mice.

CONCLUSIONS AND IMPLICATIONS

These results identify a specific role for α1-GABA_A receptors and α2-GABA_A receptors in mediating the shortening by benzodiazepines of the expiratory and inspiratory phase of resting breathing respectively.     

Über 3-Piperidino-1-phenyl-1-bicycloheptenyl-propanol-(1) (Akineton)

Ohne Zusammenfassung     

Binding sites of α1- and α2-adrenoreceptors

Conclusions The models constructed for the binding sites of rat brain ₁-AR and ₂-AR satisfy all the steric requirements and energy characteristics of interaction with known ligands, cited in [5–7, 14]. The differences detected in the arrangement and orientation of the functional groups of the binding sites permit an explanation of a whole series of typical differences in the interaction of adrenoactive substances with both subtypes of-AR.Our analysis showed that the greatest contribution to the interaction with the receptor is made by ionic, donor-acceptor, and hydrophobic bonds. The role of van der Waals forces in the interactions examined is evidently extremely negligible. The most effective and specific preparations prove to be compounds that not only form the maximum number of donor-acceptor bonds with the receptor but also orient their own hydrophobic fragments in such a way that the ionic and donor-acceptor bonds formed between the molecule and the receptor are shielded from contact with the aqueous phase. The energy effects of hydrophobic interactions of this type may be rather substantial (3.9–3.12).The production of new synthetic preparations, for which the conditions of complementarity to the-AR will be most fully satisfied, can be carried out taking the requirements of structural correspondence of the topography of the binding sites into account.Translated from Khimiko-farmatsevticheskii Zhurnal, Vol. 18, No. 8, pp. 904–912, August, 1984.     

Dicentrine is preferentially antagonistic to rat aortic than splenic α_(1-)adrenoceptor stimulation

AIM: Dicentrine is a known α1-adrenoceptor antagonist, but its 1α-adrenoceptor subtype selectivity has not yet been determined. We therefore, investigated the putative α1-adrenoceptor subtype selectivity of this agent. METHODS : Graded isometric contractile responses of rat aortic rings and spleen to phenylephrine were observed in the absence or presence of various concentrations of dicentrine. The pA2 values for dicentrine were determined. RESULTS: Aortic tissues were more sensitive to phenylephrine-induced contraction than the spleen tissues. Dicentrine was approximately 100 times more potent as an antagonist to the aortic contraction, than it was to the splenic contractions. CONCLUSION: Dicentrine is an α1-adrenoceptor antagonist which is more selective towards the putative α1D-adrenoceptor subtype of the rat aorta than the α1B-adrenoceptor of the spleen.     

实验诊断学(1)

实验诊断亦称检验诊断，属于检验医学范畴。检验医学是一门由多学科多专业组成的繁复而庞杂的综合学科，它涵盖了生物化学、血液学及细胞遗传学、医学微生物学、寄生虫学、血清免疫学及临床细胞学等多学科多专业，统称实验医学，是临床医学和预防医学的重要组成部分。检验医学是在实验室内通过对人体各种标本进行观察、检测、分析判断，从而获得临床诊断信息或依据的科学，故称之为实验诊断学，包括：病原学诊断、血清学诊断、细胞学诊断等。     

心电图基本知识(1)

什么是心电图?我们的心脏之所以能够进行收缩和舒张运动,是因为心肌细胞能够产生生物电,当这种生物电经人体组织传递到体表时,用心电图机把这些生物电记录下来,描记成曲线,并给予适当的解释,就是心电图.简单地说,就是用心电图机记录下心脏活动过程中所产生的生物电.     

考试复习题(1)

应读者要求,本刊自2014年第1期起,新辟"执业医师资格考试习题"专栏,旨在帮助正在准备迎接临床执业医师资格考试的基层医生复习做参考。这部分试题是在环球医学网校支持下,依据考试大纲模拟的,将按期连载。环球医学网校是一家医学教育、培训机构(网址:www.yx24.com),该校秉持"环球医学网医网览天下"的目标,专注基层医生的需求,为培养农村卫生人才不懈努力。欢迎读者关注本栏,访问网址www.yx24.com和www.crmp.cn,并将复习中遇到的问题及时反馈给我们。     

腹部超声讲座(11) 胰腺(1)

胰腺是位于上腹部偏左的腹膜后器官.分为头、颈、体及尾四部分,通常呈头低尾高的棱柱形,长约12～15 cm,宽约3～9cm,厚约1.5～3.0 cm,重约70～100g.     

腹部超声讲座(8)胆道(1)

1胆囊 胆囊为一薄壁的梨形囊状器官,附着于肝脏的胆囊窝内(有系带者游离)。胆囊分底、体和颈三部分。胆囊壁由外向内分别为浆膜、平滑肌及内膜(粘膜)三层结构。胆囊颈起始处的膨大部称哈氏囊,与颈相连接的为胆囊管。胆囊颈和胆囊管由于细,粘膜皱襞又呈螺旋瓣状,故是结石嵌顿的好发部位。1.1 胆囊的体表投影 胆囊长轴位于右侧腹直肌外缘与右肋弓之交点。