alpha1-AR Subtypes Research Articles

Localizations and expressions of α-1A, α-1B and α-1D adrenoceptors in human ureter

This study was designed to determine the expression and localization of the alpha-adrenoceptor (AR) subtypes in human ureteral tissue. The expression of the alpha-AR subtypes was examined by immunohistochemistry using subtype selective antibodies in proximal, mid and distal ureter. Ureter samples were obtained from pathological specimens of nephroureterectomy. A single pathologist scored the expression of receptor (grade 0, no staining; grade 1, 0-25% cells positive; grade 2, 26-50% cells positive; and grade 3, greater than 50%). We compared the mean grades of alpha-AR 1A, 1B and 1D and the percentage of receptor expression with grade 2 or more between receptor subtypes in each ureter level. The expression levels of all three subtypes are altered according to the level of ureter. In the proximal ureter, the mean grades of the alpha-1A, -1B and -1D receptors were 1.0 +/- 0.5, 1.1 +/- 0.6, and 2.1 +/- 0.7. Corresponding grades in the mid and distal ureter were 1.1 +/- 0.6, 0.8 +/- 0.6 and 2.0 +/- 0.8, and 2.0 +/- 0.7, 1.8 +/- 0.6 and 2.5 +/- 0.5, respectively. When compared with percentage of high expression, in the proximal and mid ureter, alpha-1D high expression percentage was significantly higher than alpha-1A and -1B subtype (80, 10, 20, and 90, 20, 10%, respectively). In the distal ureter, alpha-1D expression was higher than alpha-1A and -1B subtype but there was no statistical significance (100, 80, 70%). The distal ureter had higher density of alpha-AR receptors than proximal and mid ureter. The expression of alpha-1A and alpha-1B AR in distal ureter was significantly higher than proximal and mid ureter. alpha-1D expression in distal ureter was also higher than proximal and mid ureter but was not statistically significant (p = 0.28, 0.19, respectively). Our results show that alpha-1A, -1B and -1D AR subtypes are localized in human ureter irrespective of location. The expression levels of subtypes are altered according to level of ureter and subtype.

Doxazosin Relaxes Ureteral Smooth Muscle and Inhibits Epinephrine-Induced Ureteral Contractility In Vitro

Although recent evidence has supported increased ureteral stone passage with selective alpha(1)-adrenergic receptor antagonists, no mechanistic study evaluating ureteral relaxation by alpha(1) antagonism has been reported to date. We evaluated whether the alpha-blocker doxazosin reduces spontaneous, and inhibits alpha(1)-agonist-induced ureteral contractility. Additionally, alpha-receptor subtypes in normal and obstructed human ureter were analyzed. We exposed porcine ureters in organ tissue baths with 0.1, 1.0, or 10 microM doxazosin and recorded the tension for 90 minutes. After the initial treatment, a concentration-response curve of epinephrine or phenylephrine (1 nM to 10 microM) was generated. The experiment was repeated with the proximal, mid-, and distal ureter. The relative expression of the alpha 1A, 1B, and 1D receptor subtypes in normal and obstructed human ureters was analyzed using immunoblotting. Doxazosin reduced the spontaneous ureteral contractility rates in a concentration-dependent fashion by 23% to 34%. A more pronounced relaxation effect by doxazosin was evident when epinephrine was introduced to the tissues. In 1 and 10-microM doxazosin-pretreated tissues, epinephrine caused 89% and 100% relaxation, respectively. Phenylephrine-induced contractions were antagonized by doxazosin but not reversed to any relaxant function. No differential expression of alpha(1)-receptor subtypes was identified in the obstructed versus normal ureters. The results of our study have shown that alpha(1)-receptor blockade decreases ureteral contractility and inverses the effect of epinephrine, providing even greater relaxation. We hypothesize that alpha receptor blockade might relax the ureter and induce stone passage by way of epinephrine activation of beta receptors. Additional studies should be performed to validate this hypothesis and to compare various alpha(1)-receptor subtype antagonists.

ST91 [2-(2,6-Diethylphenylamino)-2-imidazoline Hydrochloride]-Mediated Spinal Antinociception and Synergy with Opioids Persists in the Absence of Functional α-2A- or α-2C-Adrenergic Receptors

Agonists acting at alpha2-adrenergic receptors (alpha2ARs) produce antinociception and synergize with opioids. The alpha2ARs are divided into three subtypes, alpha(2A)AR, alpha(2B)AR, and alpha(2C)AR. Most alpha2AR agonists require alpha(2A)AR activation to produce antinociception and opioid synergy. The same subtype also mediates the side effect of sedation, which limits the clinical utility of these compounds. Identification of a non-alpha(2A)AR-mediated antinociceptive agent would enhance the therapeutic utility of alpha2AR agonists in pain management. Previous studies have suggested that the alpha2AR agonist ST91 [2-(2,6-diethylphenylamino)-2-imidazoline hydrochloride] has a nonsedating, non-alpha(2A)AR mechanism of action. We examined the pharmacology of spinal ST91 and its interaction with the delta-opioid agonist deltorphin II (Tyr-D-Ala-Phe-Glu-Val-Val-Gly amide) in mice lacking either functional alpha(2A)ARs or alpha(2C)ARs. All drugs were administered by direct lumbar puncture, and drug interactions were evaluated using isobolographic analysis. In contrast to the majority of alpha2AR agonists, ST91 potency was only moderately reduced (3-fold) in the absence of the alpha(2A)AR. Studies with the alpha2AR subtype-preferring antagonists BRL-44408 (2-[2H-(1-methyl-1,3-dihydroisoindole)methyl]-4,5-dihydroimidazole maleate) and prazosin [[4-(4-amino-6,7-dimethoxy-quinazolin-2-yl) piperazin-1-yl]-(2-furyl)methanone] and the pan-alpha2AR antagonist SKF-86466 (6-chloro-2,3,4,5-tetrahydro-3-methyl-1-H-3-benzazepine) suggest a shift from alpha(2A)AR to the other alpha2AR subtype(s) in the absence of alpha(2A)AR. Antinociceptive synergy with deltorphin II was preserved in the absence of either alpha(2A)AR or alpha(2C)AR. In conclusion, ST91 activates both alpha(2A)AR and non-alpha(2A)AR subtypes to produce spinal antinociception and opioid synergy. This study confirms that the spinal pharmacology of ST91 differs from that of other alpha2AR agonists and extends those data to include spinal synergy with opioid agonists. The unique profile of ST91 may be advantageous in pain management.

α2‐Adrenergic receptors activate cyclic AMP‐response element‐binding protein through arachidonic acid metabolism and protein kinase A in a subtype‐specific manner

On incubation with epinephrine, PC12 cells stably expressing alpha2-adrenergic receptor (alpha2-AR) undergo morphological and biochemical changes characteristic of neuron-like differentiation. The present study shows that alpha2-AR stimulation increases the phosphorylation of the transcription factor cAMP-response element-binding protein (CREB), the activity of a CRE-reporter plasmid and the expression of cyclin D1 with subtype-dependent efficiency (alpha2A approximately alpha2C >> alpha2B). The effects of epinephrine were mimicked by cell exposure to forskolin or to exogenous arachidonic acid (AA) and they were abrogated by prior treatment with the inhibitor of phospholipase C (PLC) (U73122) or the inhibitor of cytochrome P450-dependent epoxygenase, ketoconazole. On the other hand, treatment of the cells with epinephrine caused activation of protein kinase A (PKA), which was fully abolished by ketoconazole. Inhibition of PKA activity with H89 or ketoconazole abolished the effects of epinephrine on CREB, suggesting that activation of the cAMP/PKA pathway by AA epoxy-derivatives is responsible for CREB activation by alpha2-ARs. The effects of epinephrine were unaffected by LY294002. Furthermore, treatment with staurosporine, tyrphostin AG1478, PP1 or PD98059 did not change the extent of CREB phosphorylation but enhanced its transcriptional activity. Altogether, our results demonstrate that, in PC12 cells, the alpha2-AR subtypes cause phosphorylation and activation of CREB through a pathway involving stimulation of PLC, AA release, generation of epoxygenase derivative and increase of PKA activity. They also suggest attenuation of CREB transcriptional activity by mitogen-activated protein kinase, protein kinase C and Src kinases.

Examination of alpha 1 adrenoceptor subtypes in the human ureter

Urinary stone disease is a common condition affecting up to 12% of the population. Speedy elimination of ureterolithiasis in the lower part of ureters is reported with the alpha 1-blocker. This study was carried out to characterize the alpha 1 adrenoceptors (AR) subtype gene and protein expression in the proximal, medial, and distal regions of the human ureter with the aim of facilitating stone expulsion. The study was carried out on 20 volunteers. Proximal, medial and distal ureter specimens were obtained as discarded tissues after nephroureterectomy for renal pelvic or ureteral carcinoma. Proximal ureter specimens were obtained as discarded tissues after nephrectomy for renal carcinoma. Using ureter samples, real-time reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemical staining were performed. The alpha 1d subtype mRNA was highly expressed in each ureteral region, accounting for about 54% of the total AR Messenger Ribonucleic Acid. In the proximal and medial ureter, the distribution of ARs was alpha 1d > or = alpha 1a > alpha 1b as well as that of the total ureter. The distal ureter expressed the highest amount of alpha 1d ARs. The alpha 1d subtype expression tended to be high compared with the alpha 1a subtype expression. In the distal ureter, the distribution of ARs was alpha 1d > alpha 1a > alpha 1b. Immunohistochemical staining revealed that expressions of alpha 1a-AR and alpha 1d-AR were higher than that of alpha 1b-AR. According to our results, we should try the alpha 1d AR antagonist for the conservative expulsive therapy of distal ureteral stones in the highest region of alpha 1d subtype distribution.

Alpha-adrenergic mRNA subtype expression in the human nasal turbinate

Alpha-adrenergic receptor (AR) agonist drugs (e.g., epinephrine) are commonly used for upper airway procedures, to shrink the mucosa, retard absorption of local anesthetic agents, and improve visualization by limiting hemorrhage. Decongestant therapy often also includes alphaAR agonist agents, however overuse of these drugs (e.g., oxymetazoline) can result in chronic rhinitis and rebound increases in nasal secretion. Since current decongestants stimulate alphaARs non-selectively, characterization of alphaAR subtype distribution in human airway (nasal turbinate) offers an opportunity to refine therapeutic targets while minimizing side-effects. We, therefore, investigated alphaAR subtype expression in human nasal turbinate within epithelial, duct, gland, and vessel cells using in situ hybridization. Since sensitive and specific anti-receptor antibodies and highly selective alphaAR subtype ligands are currently unavailable, in situ hybridization was performed on sections of three human nasal turbinate samples to identify distribution of alphaAR subtype mRNA. Subtype specific (35)S-labelled mRNA probes were incubated with nasal turbinate sections, and protected fragments remaining after RNase treatment analyzed by light and darkfield microscopy. In non-vascular tissue alpha(1d) AR mRNA predominates, whereas notably the alpha(2c) is the only alphaAR subtype present in the sinusoids and arteriovenous anastamoses. Combined with the current understanding that AR-mediated constriction of nasal sinusoids underpins decongestant therapies that minimize secretions and shrink tissues for airway procedures, these findings suggest that alpha(2c) AR subtypes provide a novel selective target for decongestant therapy in humans.

Epigenetic regulation of human α1d‐adrenergic receptor gene expression: a role for DNA methylation in Spl‐dependent regulation

A growing body of evidence implicates alpha1-adrenergic receptors (alpha1ARs) as potent regulators of growth pathways. The three alpha1AR subtypes (alpha1aAR, alpha1bAR, alpha1dAR) display highly restricted tissue expression that undergoes subtype switching with many pathological stimuli, the mechanistic basis of which remains unknown. To gain insight into transcriptional pathways governing cell-specific regulation of the human alpha1dAR subtype, we cloned and characterized the alpha1dAR promoter region in two human cellular models that display disparate levels of endogenous alpha1dAR expression (SK-N-MC and DU145). Results reveal that alpha1dAR basal expression is regulated by Sp1-dependent binding of two promoter-proximal GC boxes, the mutation of which attenuates alpha1dAR promoter activity 10-fold. Mechanistically, chromatin immunoprecipitation data demonstrate that Sp1 binding correlates with expression of the endogenous gene in vivo, correlating highly with alpha1dAR promoter methylation-dependent silencing of both episomally expressed reporter constructs and the endogenous gene. Further, analysis of methylation status of proximal GC boxes using sodium bisulfite sequencing reveals differential methylation of proximal GC boxes in the two cell lines examined. Together, the data support a mechanism of methylation-dependent disruption of Sp1 binding in a cell-specific manner resulting in repression of basal alpha1dAR expression.

WB4101-Related Compounds: New, Subtype-Selective α1-Adrenoreceptor Antagonists (or Inverse Agonists?)

Our previous structure-affinity relationship study had considered the enantiomers of the naphthodioxane, tetrahydronaphthodioxane, and 2-methoxy-1-naphthoxy analogues (compounds 1, 3, and 2, respectively) of 2-(2,6-dimethoxyphenoxyethylaminomethyl)-1,4-benzodioxane, the well-known alpha1-adrenoceptor (alpha1-AR) antagonist WB4101, showing that such modifications significantly modulate the affinity and selectivity profile for alpha1-AR subtypes and 5-HT1A receptor. Here, we extend investigations to antagonist activity enclosing new enantiomeric pairs, namely those of the methoxytetrahydronaphthoxy and methoxybiphenyloxy WB4101 analogues (4 and 5-7, respectively) and of a double-modified WB4101 derivative (8) resulting from hybridization between 2 and 3. We found that (S)-2 is a very potent (pA2 10.68) and moderately selective alpha1D-AR antagonist and the hybrid (S)-8 is a potent (pA2 7.98) and highly selective alpha1A-AR antagonist. Both of these compounds and (S)-WB4101 seem to act as inverse agonists in a vascular model. The results, which generally validate the logic we followed in designing these eight compounds, are acceptably rationalized by comparative SAR analysis of binding and functional affinities.

Alpha-adrenoceptor gene variants and autonomic nervous system function in a young healthy Japanese population

alpha(1A)-adrenergic receptor (alpha(1A)-AR) regulates the cardiac and peripheral vascular system through sympathetic activation, and alpha(2A)-AR and alpha(2C)-AR subtypes are essential for presynaptic feedback regulation of catecholamine release from the central and peripheral sympathetic nerve. Genetic variations in each human alpha-AR subtype gene have been identified and have been implicated in hypertension and cardiovascular disease. It is not yet clear whether these genetic variations actually have an effect on sympatho-vagal modulation. The aim of the present study was to evaluate the relation between the five representative genetic polymorphisms of alpha-AR subtypes (Arg347Cys of alpha(1A)-AR; C-1291G, Asn251Lys, and DraI RFLP of alpha(2A)-AR; and Del322-325 of alpha(2C)-AR) and autonomic nervous system (ANS) function in young and healthy Japanese males. One hundred forty-nine subjects were genotyped for each alpha-AR polymorphism, and underwent evaluation of ANS function by power spectral analysis of heart rate variability (HRV) during supine rest and in a standing position. In a supine position, the alpha(1A)-AR 347Cys allele was significantly associated with lower HRV sympathetic index (normalized low frequency power [LF(%)] and LF:HF ratio) and higher HRV parasympathetic index [HF(%)]. Meanwhile, subjects with the alpha(2C)-AR Del322-325 allele had markedly higher LF(%) and LF:HF ratio and lower HF(%) than noncarriers. Thus, the alpha(1A)-AR and alpha(2C)-AR genetic variations influence sympatho-vagal balance even in young and healthy normotensive states, which could be postulated to constitute an intermediate phenotype for future pathological episodes of various ANS dysfunction-related diseases.

Centrally Acting Imidazolines Stimulate Vascular Alpha 1A-Adrenergic Receptors in Rat-Tail Artery

: 1. Centrally acting imidazoline antihypertensive agents clonidine and moxonidine also act peripherally to contract blood vessels. While these agents act at both I(1)-imidazoline and alpha 2 adrenergic receptors centrally, the receptor types by which they mediate contraction require further definition. We therefore characterized the receptor subtype by which these agents mediate contraction of proximal rat-tail artery. 2. Dose-response curves were determined for phenylephrine and for several imidazoline ligands, using endothelium denuded, isolated ring segments, of tail arteries from adult male Sprague-Dawley rats. Ring segments were mounted on a force transducer with platinum wires and immersed in a tissue bath containing Krebs solution, to which drugs could be added. Signals were digitized and recorded by a computer. 3. Tail artery contractions expressed as a percent of contraction to 106 mM potassium were phenylephrine (96%), moxonidine (88%), clonidine (52%), and UK14304 (30%). Neither rilmenidine nor harmane caused contraction. Contraction of tail artery to moxonidine or clonidine could be blocked by alpha 1 antagonist urapidil or prazosin, and also by alpha 1A subtype selective antagonist WB4101. Schild plots were generated and a calculated pA2 value of 9.2 for prazosin in the presence of clonidine confirms clonidine as an agonist at alpha 1A receptors in proximal segments of rat-tail artery. 4. Our work suggests that clonidine and moxonidine are promiscuous compounds at micromolar concentrations and that harmane and rilmenidine are more selective compounds for in vivo imidazoline research.

Cardiac 7-transmembrane-spanning domain receptor portfolios: diversify, diversify, diversify

Enhanced signaling in myocytes by the G protein Gq has been implicated in cardiac hypertrophy and the transition to heart failure. alpha1-Adrenergic receptors (alpha1-ARs) are members of the 7-transmembrane-spanning domain (7-TM) receptor family and signal via interaction with Gq in the heart. The specific effects of a loss of alpha1-AR signaling in the heart are explored by O'Connell et al. in this issue of the JCI (see the related article beginning on page 1005). Paradoxically, gene ablation of the alpha 1A and alpha 1B subtypes in mice results in a maladaptive form of reactive cardiac hypertrophy from pressure overload, with a predisposition to heart failure. Thus signaling to the alpha1-AR (compared with signaling from other receptors such as angiotensin receptors, which also couple to Gq) appears to be specifically required for a normal hypertrophic response. This represents another example of how receptors that share common G proteins have diversified, developing unique signaling programs. These findings may have particular clinical relevance because of the widespread use of alpha1-AR antagonists in the treatment of hypertension and symptomatic prostate enlargement.

1-Adrenergic receptors prevent a maladaptive cardiac response to pressure overload

An alpha1-adrenergic receptor (alpha1-AR) antagonist increased heart failure in the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), but it is unknown whether this adverse result was due to alpha1-AR inhibition or a nonspecific drug effect. We studied cardiac pressure overload in mice with double KO of the 2 main alpha1-AR subtypes in the heart, alpha 1A (Adra1a) and alpha 1B (Adra1b). At 2 weeks after transverse aortic constriction (TAC), KO mouse survival was only 60% of WT, and surviving KO mice had lower ejection fractions and larger end-diastolic volumes than WT mice. Mechanistically, final heart weight and myocyte cross-sectional area were the same after TAC in KO and WT mice. However, KO hearts after TAC had increased interstitial fibrosis, increased apoptosis, and failed induction of the fetal hypertrophic genes. Before TAC, isolated KO myocytes were more susceptible to apoptosis after oxidative and beta-AR stimulation, and beta-ARs were desensitized. Thus, alpha1-AR deletion worsens dilated cardiomyopathy after pressure overload, by multiple mechanisms, indicating that alpha1-signaling is required for cardiac adaptation. These results suggest that the adverse cardiac effects of alpha1-antagonists in clinical trials are due to loss of alpha1-signaling in myocytes, emphasizing concern about clinical use of alpha1-antagonists, and point to a revised perspective on sympathetic activation in heart failure.

α1‐Adrenoceptor subtypes in isolated corporal tissue from patients undergoing gender re‐assignment

To investigate the pharmacology and functionality of alpha(1)-adrenoceptors in human corpus cavernosum, and to determine the predominant subtype. Cavernosal tissue specimens were obtained from the penises of 22 men (mean age 37.4 years) removed during gender re-assignment surgery. The men had been maintained on long-term oestrogen therapy before surgery, to aid the development of secondary feminine characteristics (oestrogen treatments were stopped 6 weeks before surgery). Corpus cavernosum strips were mounted in organ baths perfused with Krebs' solution. A control concentration-response curve (CRC) to phenylephrine (a nonselective alpha(1)-agonist) was obtained. Then the tissues were incubated with the alpha(1A) antagonist, WB4101; the alpha(1B) antagonist, chloroethylclonidine; or the alpha(1D) antagonist BMY 7378 (all at 1 microm) and the CRC to phenylephrine was repeated. The concentration producing a half-maximal response (EC(50)) and pK(B) values (logarithm of the dissociation constant, a measure of affinity) were determined. WB4101 produced a parallel rightward shift of the CRC to phenylephrine, with a pK(B) of 7.49. BMY 7378 also produced a parallel rightward shift of the CRC to phenylephrine with a pK(B) of 6.45. Chloroethylclonidine had a similar effect on the phenylephrine CRC, with a pK(B) of 5.90. Alpha(1)-adrenoceptors in human cavernosal tissue have a relatively low affinity for BMY 7378 and chloroethylclonidine, but are more sensitive to WB4101. This confirms that the predominant alpha(1)-adrenoceptor subtype in human corpus cavernosum is the alpha(1A) subtype and this might help in developing more selective antagonists and agonists for managing erectile dysfunction and priapism.

Effects of a α2C-Adrenoreceptor Gene Polymorphism on Neural Responses to Facial Expressions in Depression

Alterations in processing of emotionally salient information have been reported in individuals with major depressive disorder (MDD). Evidence suggests a role for noradrenaline in the regulation of a cortico-limbic-striatal circuit that has also been implicated in the pathophysiology of MDD. Herein, we studied the physiological consequences of a common coding polymorphism of the gene for the alpha(2C)-adrenoreceptor (AR) subtype--the deletion of four consecutive amino acids at codons 322-325 of the alpha2C-AR (alpha2CDel322-325-AR) in medication-free, remitted individuals with MDD (rMDD), and healthy control subjects. After injection of 10 mCi of H2(15)O, positron emission tomography (PET) measures of neural activity were acquired while subjects were viewing unmasked sad, happy, and fearful faces. The neural responses to sad facial expressions were increased in the amygdala and decreased in the left ventral striatum in rMDD patients relative to healthy control subjects. Furthermore, we report that rMDD carriers of one or two copies of the alpha2CDel322-325-AR exhibit greater amygdala as well as pregenual and subgenual anterior cingulate gyrus neuronal activity in response to sad faces than healthy alpha2CDel322-325-AR carriers and rMDD noncarriers. These results suggest that the alpha2CDel322-325-AR confers a change in brain function implicating this alpha2-AR subtype into the pathophysiology of MDD.

Differentiated rabbit prostatic stromal cells in primary culture display functional α1A‐adrenoceptors

BPH is characterized by uncontrolled proliferation and increased contractility of prostatic smooth muscle cells. The activation of alpha1-adrenoceptors (alpha1-AR) seems involved in the latter event, but the lack of in vitro models expressing these receptors has hampered a more specific characterization of their role. In order to do so, we attempted to develop a new model of rabbit cultured prostatic stromal cells (PSC) in a non-proliferative and differentiated state. The expression of cytoskeletal and stromal markers was confirmed by immunohistochemistry on primary cultured PSC. Alpha1-AR subtype expression was assessed by RT-PCR, while receptor coupling to the ERK1/ERK2 and calcium pathways was studied by Western Blot and Fura-2 calcium imaging, respectively. Cells grown under non-proliferative conditions displayed a differentiated phenotype, with expression of contractile cytoskeletal and stromal proteins. Furthermore, the alpha1A-AR was shown to activate ERK1/ERK2 as well as calcium signaling. These results emphasize the interest of this model for the characterization of PSC adrenergic regulation, in particular through the little-known alpha1A-AR.

Recent progress in alpha1-adrenergic receptor research

Alpha1-Adrenergic receptors (AR) play an important role in the regulation of physiological responses mediated by norepinephrine and epinephrine, particularly in the cardiovascular system. The three cloned alpha1-AR subtypes (alpha1A, alpha1B, and alpha1D) are G protein-coupled receptors that signal through the Gq/11 signaling pathway, each showing distinct pharmacological properties and tissue distributions. However, due to the lack of highly subtype-selective drugs, the functional roles of individual subtypes are still not clear. Development of new subtype-specific drugs will greatly facilitate the identification of the functions of each subtype. Conopeptide rho-TIA has been found to be a new alpha1B-AR selective antagonist with different modes of inhibition at alpha1-AR subtypes. In addition, recent studies using genetically engineered mice have shed some light on alpha1-AR functions in vivo, especially in the cardiovascular system and brain. Several proteins have been shown to interact directly with particular alpha1-AR, and may be important in regulating receptor function. Receptor heterodimerization has been shown to be important for cell surface expression, signaling and internalization. These new observations are likely to help elucidate the functional roles of individual alpha1-AR subtypes.

Comparison of tamsulosin and naftopidil for efficacy and safety in the treatment of benign prostatic hyperplasia: a randomized controlled trial

To compare the efficacy and safety of two alpha1a/alpha1d adrenoceptor (AR) antagonists with different affinity for the alpha1AR subtypes, tamsulosin and naftopidil, in the treatment of benign prostatic hyperplasia (BPH). Patients with BPH were randomized to receive either tamsulosin or naftopidil. The primary efficacy variables were the changes in the total International Prostate Symptom Score (IPSS), maximum flow rate on free uroflowmetry, and residual urine volume. The secondary efficacy variables were average flow rate, changes in the IPSS storage score, IPSS voiding score, and quality-of-life (QoL) Index score, from baseline to endpoint (12 weeks). Data on all randomized patients were included in the safety analyses for adverse effects and changes in blood pressure. Of the 185 patients enrolled data for 144 who were eligible for inclusion in the efficacy analysis were analysed (75 from the tamsulosin and 69 from the naftopidil group). There was no significant difference in any variable at baseline between the groups. There were statistically significant improvements for all primary and secondary variables in both groups, except for residual urine in the tamsulosin group. However, there was no significant intergroup difference in the improvement of any efficacy variable between the groups. The adverse effects were comparable, with no significant differences in systolic and diastolic blood pressure after treatment in both groups. This study suggests that naftopidil is as effective and safe as tamsulosin. Both drugs were effective in improving storage and voiding symptoms. However, there was no difference in clinical efficacy or adverse effects between the alpha1 AR antagonists with different affinity to alpha1 subtypes, alpha1a and alpha1d.

8-NH2-Boldine, an Antagonist of α1Aand α1BAdrenoceptors without Affinity for the α1DSubtype: Structural Requirements for Aporphines at α1-Adrenoceptor Subtypes

Structure-activity analysis of 21 aporphine derivatives was performed by examining their affinities for cloned human alpha (1A), alpha (1B) and alpha (1D) adrenoceptors (AR) using membranes prepared from rat-1 fibroblasts stably expressing each alpha (1)-AR subtype. All the compounds tested competed for [ (125)I]-HEAT binding with steep and monophasic curves. The most interesting compound was 8-NH (2)-boldine, which retains the selective affinity for alpha(1A)-AR (pKi = 6.37 +/- 0.21) vs. alpha(1B)-AR (pKi = 5.53 +/- 0.11) exhibited by 1,2,9,10-tetraoxygenated aporphines, but shows low affinity for alpha(1D)-AR (pKi < 2.5). Binding studies on native adrenoceptors present in rat cerebral cortex confirms the results obtained for human cloned alpha (1)-AR subtypes. The compounds selective for the alpha (1A) subtype discriminate two binding sites in rat cerebral cortex confirming a mixed population of alpha (1A)- and alpha (1B)-AR in this tissue. All compounds are more selective as inhibitors of [ (3)H]-prazosin binding than of [ (3)H]-diltiazem binding to rat cerebral cortical membranes. A close relationship was found between affinities obtained for cloned alpha (1A)-AR and inhibitory potencies on noradrenaline-induced contraction or inositol phosphate accumulation in tail artery, confirming that there is a homogeneous functional population of alpha(1A)-AR in this vessel. On the contrary, a poor correlation seems to exist between the affinity of 8-NH (2)-boldine for cloned alpha (1D)-AR and its potency as an inhibitor of noradrenaline-induced contraction or inositol phosphate accumulation in rat aorta, which confirms that a heterogeneous population of alpha (1)-AR mediates the adrenergic response in this vessel.

FUNCTION OF THE LOWER URINARY TRACT IN MICE LACKING α 1d-ADRENOCEPTOR

alpha1-Adrenoceptor (AR) blockers are known to relieve not only voiding symptoms, but also storage symptoms in elderly men. We investigated lower urinary tract function in mice lacking alpha1d-AR using frequency/volume analysis and filling cystometry. A total of 10, 12-week-old female alpha1d-knockout (KO) mice and 10 age matched female wild-type (WT) mice were studied. Each mouse was placed in a metabolic cage connected to a digital scale and personal computer. Under a 12/12-hour dark/light photocycle voiding frequency and volume were recorded for 48 hours. After frequency/volume analysis filling cystometry was performed with the mice awake and without restraint. The expression of alpha1-AR subtype mRNA in the bladder of mice in each group was quantified using real-time polymerase chain reaction. Mean daily voiding frequency +/- SD in alpha1d-KO mice was 9.0 +/- 2.1, significantly lower than 15.9 +/- 5.2 in WT mice (p = 0.0048). Mean volume per void in alpha1d-KO mice was significantly larger than in WT mice (0.24 +/- 0.02 vs 0.16 +/- 0.03 ml, p = 0.0096). Similarly cystometric analysis demonstrated larger bladder capacity (140%, p = 0.0008) and voided volume (146%, p = 0.0048) in alpha1d-KO mice compared with those in WT mice. No significant difference in maximum pressure at void was observed between the 2 groups. In WT mice the amount of alpha1a, alpha1b and alpha1d-AR subtype mRNA in the bladder was 5.2 +/- 0.7, 1.0 +/- 0.1 and 6.3 +/- 0.7 gene copies per ng total RNA, respectively. In contrast, alpha1d-AR transcript was not detectable in alpha1d-KO mice but alpha1a and alpha1b-AR expression was similar to that in WT mice. The results demonstrate that the alpha1d-AR subtype has an important role in regulating bladder function. They theoretically support a clinical finding that alpha1-blockers with significant affinity for alpha1d-AR are effective for treating storage symptoms associated with benign prostatic obstruction.

Transcutaneous electrical nerve stimulation activates peripherally located alpha-2A adrenergic receptors

The alpha 2A and alpha 2C adrenergic receptor (AR) subtypes mediate antinociception when activated by the endogenous ligand norepinephrine. These receptors also produce antinociceptive synergy when activated concurrently with opioid receptor activation. The involvement of the opioid receptors in the mechanisms governing transcutaneous electrical nerve stimulation (TENS) has been well described. While spinal alpha-2 ARs do not appear to be involved in TENS antihyperalgesia in rats, the noradrenergic analgesic system also involves supraspinal and peripheral sites. Thus, a broader evaluation of the potential contribution of alpha-2 AR to TENS is warranted. The current study compared the antihyperalgesic efficacy of high (100 Hz) and low (4 Hz) frequency TENS in mutant mice lacking a functional alpha 2A AR against their respective wildtype counterparts. The degree of secondary heat hyperalgesia induced by intra-articular injection of carrageenan/kaolin (3%) mixture did not differ among the experimental groups. However, the antihyperalgesia induced by both low and high frequency TENS was significantly diminished in alpha 2A mutant mice compared to controls. The alpha 2 adrenergic receptor selective antagonist, SK&F 86466, reversed TENS-mediated antihyperalgesia when delivered intra-articularly, but not when delivered intrathecally or intracerebroventricularly. These data suggest that peripheral alpha 2 ARs contribute, in part, to TENS antihyperalgesia. This pharmacodynamic response is consistent with previous anatomical observations that alpha 2A ARs are expressed on primary afferent neurons and macrophages near injured tissue.