Alpha 1D- and alpha 1A-adrenoceptors mediate contraction in rat renal artery

A Prospective, Multicenter, Open-Label Study of Dose Escalation Therapy in Male Patients With Nocturia Refractory to 0.2-mg Tamsulosin Monotherapy

Purpose

To investigate the efficacy and safety of 0.4 mg of tamsulosin in patients with nocturia not responding to 0.2 mg.

Methods

Patients with intractable nocturia after treatment with 0.2 mg of tamsulosin for>1 month were included in a multicenter, prospective, observational, single-arm study. Patients were prescribed 0.4 mg of tamsulosin and followed up for 2 months to assess nocturnal voiding and nocturia-related bother. Changes in the mean number of nocturnal voids, the proportion of 50% responders, 3-day frequency-volume chart parameters, and questionnaire scores were assessed.

Results

Sixty-two patients were prescribed 0.2 mg of tamsulosin, of whom 56 were prescribed 0.4 mg of tamsulosin. Ten patients dropped out. A single case of orthostatic hypotension was reported. The mean age was 68 years. After 1 and 2 months of taking 0.4 mg of tamsulosin, 23.9% and 22.7% of patients demonstrated a>50% reduction of nocturia, and 16.1% and 19.4% of patients rated the treatment as “very effective,” respectively. Dose escalation to 0.4 mg of tamsulosin, compared to 0.2 mg, did not show an additional effect on reducing nocturnal urine volume. Multivariate logistic regression analysis showed that lower serum sodium levels (odds ratio [OR], 0.41, P=0.037) and the presence of urge incontinence (OR, 7.08, P=0.036) were predictors of a significant improvement of nocturia in response to 0.4 mg of tamsulosin.

Conclusions

Dose escalation may yield a significant improvement of nocturia in>20% of patients, and may be especially helpful in patients with lower sodium levels and urge incontinence.

Role of Nitric Oxide in the Cardiovascular and Renal Systems

The gasotransmitters are a family of gaseous signaling molecules which are produced endogenously and act at specific receptors to play imperative roles in physiologic and pathophysiologic processes. As a well-known gasotransmitter along with hydrogen sulfide and carbon monoxide, nitric oxide (NO) has earned repute as a potent vasodilator also known as endothelium-derived vasorelaxant factor (EDRF). NO has been studied in greater detail, from its synthesis and mechanism of action to its physiologic, pathologic, and pharmacologic roles in different disease states. Different animal models have been applied to investigate the beneficial effects of NO as an antihypertensive, renoprotective, and antihypertrophic agent. NO and its interaction with different systems like the renin–angiotensin system, sympathetic nervous system, and other gaseous transmitters like hydrogen sulfide are also well studied. However, links that appear to exist between the endocannabinoid (EC) and NO systems remain to be fully explored. Experimental approaches using modulators of its synthesis including substrate, donors, and inhibitors of the synthesis of NO will be useful for establishing the relationship between the NO and EC systems in the cardiovascular and renal systems. Being a potent vasodilator, NO may be unique among therapeutic options for management of hypertension and resulting renal disease and left ventricular hypertrophy. Inclusion of NO modulators in clinical practice may be useful not only as curatives for particular diseases but also for arresting disease prognoses through its interactions with other systems.

Maternal separation diminishes α-adrenergic receptor density and function in renal vasculature from male Wistar-Kyoto rats

Adult rats exposed to maternal separation (MatSep) are normotensive but display lower glomerular filtration rate and increased renal neuroadrenergic drive. The aim of this study was to determine the renal α-adrenergic receptor density and the renal vascular responsiveness to adrenergic stimulation in male rats exposed to MatSep. In addition, baroreflex sensitivity was assessed to determine a component of neural control of the vasculature. Using tissue collected from 4-mo-old MatSep and control rats, α₁-adrenergic receptors (α₁-ARs) were measured in renal cortex and isolated renal vasculature using receptor binding assay, and the α-AR subtype gene expression was determined by RT-PCR. Renal cortical α₁-AR density was similar between MatSep and control tissues (B_max = 44 ± 1 vs. 42 ± 2 fmol/mg protein, respectively); however, MatSep reduced α₁-AR density in renal vasculature (B_max = 47 ± 4 vs. 62 ± 4 fmol/mg protein, P < 0.05, respectively). In a separate group of rats, the pressor, bradycardic, and renal vascular constrictor responses to acute norepinephrine injection (NE, 0.03-0.25 μg/μl) were determined under anesthesia. Attenuated NE-induced renal vasoconstriction was observed in rats exposed to MatSep compared with control (P < 0.05). A third group of rats was infused at steady state with the α₁ agonist phenylephrine (10 μg/min iv) and vasodilator sodium nitroprusside (5 μg/min iv). The difference between the change in heart rate/mean arterial pressure slopes was indicative of reduced baroreflex sensitivity in MatSep vs. control rats (-0.45 ± 0.04 vs. -0.95 ± 0.07 beats·min^-1·mmHg^-1, P < 0.05). These data support the notion that reduced α-adrenergic receptor expression and function in the renal vasculature could develop secondary to MatSep-induced overactivation of the renal neuroadrenergic tone.

LPA receptor activity is basal specific and coincident with early pregnancy and involution during mammary gland postnatal development

During pregnancy, luminal and basal epithelial cells of the adult mammary gland proliferate and differentiate resulting in remodeling of the adult gland. While pathways that control this process have been characterized in the gland as a whole, the contribution of specific cell subtypes, in particular the basal compartment, remains largely unknown. Basal cells provide structural and contractile support, however they also orchestrate the communication between the stroma and the luminal compartment at all developmental stages. Using RNA-seq, we show that basal cells are extraordinarily transcriptionally dynamic throughout pregnancy when compared to luminal cells. We identified gene expression changes that define specific basal functions acquired during development that led to the identification of novel markers. Enrichment analysis of gene sets from 24 mouse models for breast cancer pinpoint to a potential new function for insulin-like growth factor 1 (Igf1r) in the basal epithelium during lactogenesis. We establish that β-catenin signaling is activated in basal cells during early pregnancy, and demonstrate that this activity is mediated by lysophosphatidic acid receptor 3 (Lpar3). These findings identify novel pathways active during functional maturation of the adult mammary gland.

Effect of inter-renal aortic coarctation-induced hypertension on function and expression of vascular α(1A)- and α(1D)-adrenoceptors

We investigated the effect of inter-renal aortic coarctation on the function and expression of vascular α(1A)- and α(1D)-adrenoceptors and plasma angiotensin II (ATII) in rats. Male Wistar rats, either sham operated (SO), or with aortic coarctation for 7 (AC7) and 14 days (AC14) were used for agonist-induced pressor responses in vehicle (physiological saline)- and antagonist-treated anesthetized animals, immunoblot analysis (α(1A)- and α(1D)-adrenoceptor in aorta and caudal arteries), and immunoassay (plasma ATII). The α(1D)-adrenoceptor antagonist, BMY-7378 (BMY) blocked noradrenaline-induced responses in the order SO > AC7 ≫ AC14; in contrast, the α(1A)-adrenoceptor antagonist RS-100329 (RS), produced a marginal shift to the right of the dose-response curve to noradrenaline, along with a strong decrease of the maximum pressor effect in the order SO > AC7 = AC14. The potency of the α(1A)-adrenoceptor agonist A-61603 increased in rats with AC14, and responses were inhibited by RS in the order AC14 > AC7 > SO. In aorta, α(1D)-adrenoceptor protein increased in AC7 and decreased in AC14; α(1A)-adrenoreceptor protein increased in the caudal artery of AC7 and returned to control values in AC14. Plasma ATII increased in AC7 and AC14, compared with SO rats. These results suggest an early and direct relationship between ATII and α(1D)-adrenoreceptors in the development of hypertension in this experimental model.

Transactivated EGFR mediates α1-AR-induced STAT3 activation and cardiac hypertrophy

Li Y, Zhang H, Liao W, Song Y, Ma X, Chen C, Lu Z, Li Z, Zhang Y. α1-Adrenergic receptor (α1-AR) is a crucial mediator of cardiac hypertrophy. Although numerous intracellular pathways have been implicated in α1-AR-induced hypertrophy, its precise mechanism remains elusive. We aimed to determine whether α1-AR induces cardiac hypertrophy through a novel signaling pathway-α1-AR/epidermal growth factor receptor (EGFR)/signal transducer and activator of transcription 3 (STAT3). The activation of STAT3 by α1-AR was first demonstrated by tyrosine phosphorylation, nuclear translocation, DNA binding, and transcriptional activity in neonatal Sprague-Dawley rat cardiomyocytes. Activated STAT3 showed an essential role in α1-AR-induced cardiomyocyte hypertrophic growth, as assessed by treatment with STAT3 inhibitory peptide and lentivirus-STAT3 small interfering RNA. The results were further confirmed by in vivo experiments involving intraperitoneal injection of the STAT3 inhibitor WP1066 significantly inhibiting phenylephrine-infusion-induced heart hypertrophy in male C57BL/6 mice. Furthermore, the α1-AR-activated STAT3 was associated with transactivation of EGFR because inhibition of EGFR with the selective inhibitor AG1478 prevented α1-AR-induced STAT3 tyrosine phosphorylation and its transcriptional activity, as well as cardiac hypertrophy. In summary, these results suggest that α1-AR induces the activation of STAT3, mainly through transactivation of EGFR, which plays an important role in α1-AR-induced cardiac hypertrophy.

High-fructose feeding impacts on the adrenergic control of renal haemodynamics in the rat

The present study explored the hypothesis that a prolonged 8 weeks exposure to a high fructose intake suppresses adrenergic and angiotensin II (Ang II)-mediated vasoconstriction and is associated with a higher contribution of α1D-adrenoceptors. A total of thirty-two Sprague–Dawley rats received either 20 % fructose solution (FFR) or tap water (control, C) to drink ad libitum for 8 weeks. Metabolic and haemodynamic parameters were assessed weekly. The renal cortical vasoconstrictor responses to noradrenaline (NA), phenylephrine (PE), methoxamine (ME) and Ang II were determined in the presence and absence of BMY7378 (α1D-adrenoceptor antagonist). FFR had increased blood pressure, plasma levels of glucose, TAG and insulin. FFR expressed reduced renal vascular responses to adrenergic agonists and Ang II (NA: 50 %, PE: 50 %, ME, 65 %, Ang II: 54 %). Furthermore in the C group, the magnitude of the renal cortical vasoconstriction to all agonists was blunted in the presence of the low or high dose of BMY7378 (NA: 30 and 31 %, PE: 23 and 33 %, ME: 19 and 44 %, Ang II: 53 and 77 %), respectively, while in the FFR, vasoconstriction was enhanced to adrenergic agonists and reduced to Ang II (NA: 8 and 83 %, PE: 55 %, ME, 2 and 177 %, Ang II: 61 and 31 %). Chronic high fructose intake blunts vascular sensitivity to adrenergic agonists and Ang II. Moreover, blocking of the α1D-adrenoceptor subtype results in enhancement of renal vasoconstriction to adrenergic agonists, suggesting an inhibitory action of α1D-adrenoceptors in the FFR. α1D-Adrenoceptors buffer the AT1-receptor response in the renal vasculature of normal rats and fructose feeding suppressed this interaction.

Evidence for the role of α1A-adrenoceptor subtype in the control of renal haemodynamics in fructose-fed Sprague-Dawley rat

AIM

To explore the hypothesis that high fructose intake results in a higher functional contribution of α1A-adrenoceptors and blunts the adrenergically and angiotensin II (Ang II)-induced renal vasoconstriction.

METHODS

Twelve Sprague-Dawley rats received either 20% fructose solution [FFR] or tap water [C] to drink ad libitum for 8 weeks. The renal vasoconstrictor response to noradrenaline (NA), phenylephrine (PE), methoxamine (ME) and Ang II was determined in the presence and absence of 5-methylurapidil (5-MU) (α1A-adrenoceptor antagonist) in a three-phase experiment (pre-drug, low- and high-dose 5-MU). Data, mean ± SEM were analysed by ANOVA or Student's unpaired t-test with significance at P < 0.05.

RESULTS

FFR exhibited insulin resistance (HOMA index), hypertension and significant increases in plasma levels of glucose and insulin. All agonists caused dose-related reductions in cortical blood perfusion that were larger in C than in FFR while the magnitudes of the responses were progressively reduced with increasing doses of 5-MU in both C and FFR. The degree of 5-MU attenuation of the renal cortical vasoconstriction due to NA, ME and Ang II was significantly greater in the FFR compared to C.

CONCLUSIONS

Fructose intake for 8 weeks results in smaller vascular response to adrenergic agonists and Ang II. The α1A-adrenoceptor subtype is the functional subtype that mediates renal cortical vasoconstriction in control rats, and this contribution becomes higher due to fructose feeding.

Subtypes of functional alpha1-adrenoceptor

In this review, subtypes of functional alpha1-adrenoceptor are discussed. These are cell membrane receptors, belonging to the seven-transmembrane-spanning G-protein-linked family of receptors, which respond to the physiological agonist noradrenaline. alpha1-Adrenoceptors can be divided into alpha1A-, alpha1B- and alpha1D-adrenoceptors, all of which mediate contractile responses involving Gq/11 and inositol phosphate turnover. A fourth alpha1-adrenoceptor, the alpha1L-, represents a functional phenotype of the alpha1A-adrenoceptor. alpha1-Adrenoceptor subtype knock-out mice have refined our knowledge of the functions of alpha-adrenoceptor subtypes, particuarly as subtype-selective agonists and antagonists are not available for all subtypes. alpha1-Adrenoceptors function as stimulatory receptors involved particularly in smooth muscle contraction, especially contraction of vascular smooth muscle, both in local vasoconstriction and in the control of blood pressure and temperature, and contraction of the prostate and bladder neck. Central actions are now being elucidated.

α(1D)-Adrenergic receptors constitutive activity and reduced expression at the plasma membrane

Adrenergic receptors are a heterogeneous family of the G protein-coupled receptors that mediate the actions of adrenaline and noradrenaline. Adrenergic receptors comprise three subfamilies (α(1), α(2), and β, with three members each) and the α(1D)-adrenergic receptor is one of the members of the α(1) subfamily with some interesting traits. The α(1D)-adrenergic receptor is difficult to express, seems predominantly located intracellularly, and exhibits constitutive activity. In this chapter, we will describe in detail the conditions and procedures used to determine changes in intracellular free calcium concentration which has been instrumental to define the constitutive activity of these receptors. Taking advantage of the fact that truncation of the first 79 amino acids of α(1D)-adrenergic receptors markedly increased their membrane expression, we were able to show that constitutive activity is present in receptors truncated at the amino and carboxyl termini, which indicates that such domains are dispensable for this action. Constitutive activity could be observed in cells expressing either the rat or human α(1D)-adrenergic receptor orthologs. Such constitutive activity has been observed in native rat arteries and we will discuss the possible functional implications that it might have in the regulation of blood pressure.

Arg347Cys polymorphism of alpha1A-adrenoceptor gene is associated with blood pressure response to nifedipine GITS in Chinese hypertensive patients

Our objectives were to evaluate whether polymorphisms in the alpha1A- and beta2-adrenoceptor genes influence blood pressure response to nifedipine gastrointestinal therapeutic system (GITS). Hypertensive patients received daily treatment with an oral dosage of 30 mg nifedipine GITS for 16 days. Genotypes of the Arg347Cys polymorphism in the alpha1A-adrenoceptor gene and the Arg16Gly and Gln27Glu polymorphisms in the beta2-adrenoceptor gene were determined by TaqMan single-nucleotide polymorphism genotyping assay. The sixteenth-day steady-state plasma concentration of nifedipine was measured using HPLC with UV detection. Multivariate linear regression was performed in a total of 447 patients to evaluate the effects of these polymorphisms on blood pressure response to nifedipine GITS. Patients carrying the Cys347 allele of the alpha1A-adrenoceptor gene had a greater systolic blood pressure reduction than did those carrying two Arg347 alleles of the alpha1A-adrenoceptor gene (32.5+/-14.0 versus 27.3+/-15.5 mm Hg, respectively, P=0.006). However, diastolic blood pressure reduction was not associated with the Arg347Cys polymorphism in the alpha1A-adrenoceptor gene. In addition, no significant associations were observed between blood pressure reduction and two polymorphisms in the beta2-adrenoceptor gene. Our data suggest that the Arg347Cys polymorphism in the alpha1A-adrenoceptor gene may be used to predict blood pressure response to nifedipine GITS in Chinese hypertensive patients.

Functional subtypes of renal alpha1-adrenoceptor in diabetic and non-diabetic 2K1C Goldblatt renovascular hypertension

AIM

This study investigates the subtypes of the alpha1-adrenoceptor mediating the adrenergically-induced renal vasoconstrictor responses in streptozotocin-induced diabetic and non-diabetic 2-kidney one clip (2K1C) Goldblatt hypertensive rats.

METHODS

The renal blood flow responses to renal nerve stimulation, noradrenaline, phenylephrine, and methoxamine were measured in the absence and presence of nitrendipine, 5-methylurapidil, chloroethylclonidine and BMY 7378.

RESULTS

The renal vasoconstrictor responses were markedly attenuated by nitrendipine and 5- methylurapidil in the diabetic rats (all P< 0.05). In the non-diabetic rats, these responses were markedly attenuated by nitrendipine, 5-methylurapidil, and BMY 7378 (all P< 0.05). In both experimental groups, chloroethylclonidine markedly accentuated the renal vasoconstrictions caused by all the adrenergic stimuli (all P< 0.05).

CONCLUSION

These observations indicate that alpha 1A-adrenoceptor subtypes play a major role in mediating adrenergically-induced renal vasoconstriction in the diabetic 2K1C Goldblatt hypertensive rats. In the non-diabetic 2K1C Goldblatt hypertensive rats, contributions of alpha 1A and alpha 1D-adrenoceptor subtypes were proposed. Apart from post-synaptic alpha 1-adrenoceptors, both in the diabetic and non-diabetic 2K1C Goldblatt hypertensive rats, the potential involvement of presynaptic alpha 1- adrenoceptors is also suggested.

Evidence of alpha1-adrenoceptor functional changes in omental arteries of patients with end-stage renal disease

1 Alpha1-Adrenoceptor (alpha1-AR) subtypes were characterized in isolated omental arteries obtained after abdominal surgery in patients with end-stage renal disease (ESRD) or with Diabetes Mellitus type 2 plus ESRD (ESRD-DM). 2 Omental arteries from patients with ESRD and ESRD-DM elicited a significant increase in sensitivity to phenylephrine with a pD(2) (-log EC50) of 6.7 and 6.6, respectively, vs. the control (5.8, P < 0.001). 3 Stimulation with phenylephrine was conducted in the presence or absence of selective alpha1-AR competitive antagonists: 5-methylurapidil (alpha1A-), AH11110A (1-[biphenyl-2-yloxy]-4-imino-4-piperidin-1-yl-butan-2-ol; alpha1B-) and BMY7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro [4.5] decane-7,9-dione; alpha(1D)-). The relative abundance of mRNA for all three alpha(1)-ARs was determined. 4 The maximal contractile responses to phenylephrine were: E(max) 1.59 +/- 0.17, 1.48 +/- 0.08 and 1.55 +/- 0.14 g for the ESRD, ESRD-DM and control groups, respectively. 5 Functionally, there was an increment in the affinity for the alpha(1A)-AR antagonist (pA2: control 7.45, ESRD 8.36, ESRD-DM 8.0; P < 0.01), and a reduction in the alpha1B-AR antagonist affinity (8.3 for controls, 7.6 for ESRD and 7.3 for ESRD-DM; P < 0.01) associated with renal disease. The affinities for the alpha1D-AR antagonist were similar among the studied groups (8.5 for the controls, 8.7 for the ESRD and 8.1 for the ESRD-DM groups). 6 Renal disease increased mRNA expression of alpha(1B)-ARs and reduced both alpha1A- and alpha(1D)-ARs subtypes in ESRD and ESRD-DM patients. 7 The results suggest that human omental arteries exposed to chronic uraemia show vascular hypersensitivity to phenylephrine, because of functional alpha1-AR changes.

Influence of combined hypertension and renal failure on functional alpha(1)-adrenoceptor subtypes in the rat kidney

BACKGROUND AND PURPOSE

This study investigated whether the alpha(1)-adrenoceptor responsiveness of the renal vasculature was altered in the state of hypertension combined with renal failure.

EXPERIMENTAL APPROACH

Male spontaneously hypertensive rats (SHR) received cisplatin (5 mg kg(-1) i.p.) to induce renal failure. Seven days later, the rats were anaesthetized and the reductions in renal blood flow (RBF) to electrical renal nerve stimulation (RNS) and intrarenal administration of three adrenoceptor agonists (noradrenaline, phenylephrine and methoxamine) were determined before and after amlodipine, 5-methylurapidil, chloroethylclonidine or BMY 7378.

KEY RESULTS

In renal failure SHR (RFSHR), RBF and creatinine clearance were significantly reduced (approximately 70%), while urine output and fractional sodium excretion were four and twenty-fold higher, respectively, compared to SHR. Vasoconstrictions induced by RNS or the adrenoceptor agonists were greater in RFSHR than SHR, and these responses were blunted by 5-methylurapidil, BMY 7378 and amlodipine in the SHR, while chloroethylclonidine had no effect. In the RFSHR, all renal vasoconstrictions were reduced by amlodipine and BMY 7378 but 5-methylurapidil attenuated those caused by RNS, noradrenaline and methoxamine while those to phenylephrine were enhanced. Chloroethylclonidine potentiated renal vasoconstrictor responses to methoxamine and phenylephrine but not RNS or noradrenaline in RFSHR.

CONCLUSIONS AND IMPLICATIONS

These findings suggest alpha(1A)- and alpha(1D)-adrenoceptors mediated the renal vasoconstrictor responses in SHR and RFSHR. In the RFSHR, other alpha(1)-adrenoceptor subtypes, for example, alpha(1B)-adrenoceptors appeared to play a greater role.

Alpha1B-adrenoceptors mediate adrenergically-induced renal vasoconstrictions in rats with renal impairment

AIM

This study examined whether alpha1B-adrenoceptors are involved in mediating adrenergically-induced renal vasoconstrictor responses in rats with pathophysiological and normal physiological states.

METHODS

Male Wistar Kyoto and spontaneously hypertensive rats were induced with acute renal failure or experimental early diabetic nephropathy by cisplatin or streptozotocin, respectively. Cisplatin-induced renal failure was confirmed by impaired renal function and pronounced tubular damage. Experimental early diabetic nephropathy was confirmed by hyperglycemia, changes in physiological parameters, and renal function. The hemodynamic study was conducted on anesthetized rats after 7 d of cisplatin (renal failure) and 4 weeks of streptozotocin (experimental early diabetic nephropathy).

RESULTS

In the rats with renal failure and experimental early diabetic nephropathy, there were marked reductions in their baseline renal blood flow (P<0.01). The baseline mean arterial blood pressure was either unaltered or lower (all P>0.05) in the renal failure and experimental early diabetic nephropathy rats, respectively, as compared to their non-renal failure and non-diabetic nephropathy controls. In the rats with renal impairment, chloroethylclonidine caused either accentuation or attenuation (all P<0.01) of the renal vasoconstrictor responses elicited by the adrenergic stimuli. However, in the non-renal failure and in the non-diabetic nephropathy rats, chloroethylclonidine did not cause any alteration in such responses (P>0.05).

CONCLUSION

This study demonstrated the presence of functional alpha1B-adrenoceptors that mediated the adrenergically-induced renal vasoconstrictions in rats with renal impairment, but not in rats with normal renal function.

Influence of cisplatin-induced renal failure on the α1-adrenoceptor subtype causing vasoconstriction in the kidney of the rat

This study investigated whether the alpha(1)-adrenoceptor subtype(s) mediating the vasoconstrictor actions of the renal sympathetic nerves were altered in rats with cisplatin-induced renal failure. Male Wistar Kyoto rats were used and half received cisplatin (5 mg/kg i.p.) to induce renal failure and were taken for study 7 days later. The renal blood flow reductions caused by electrical renal nerve stimulation and close intra-renal administration of noradrenaline, phenylephrine and methoxamine were determined before and after amlodopine (AMP), 5-methylurapidil (MeU), chloroethylclonidine (CEC) or BMY 7378. Water intake and creatinine clearance were decreased (P<0.05) by 40-50% while fractional excretion of sodium was increased two-fold in the cisplatin treated rats. Mean arterial pressure was higher, 110+/-2 versus 102+/-3 mmHg and renal blood flow was lower, 10.7+/-0.9 versus 18.9+/-0.1 ml/min/kg in the renal failure rats (both P<0.05). AMP, MeU and BMY 7378 decreased (all P<0.05) the adrenergically induced renal vasoconstrictor responses in the renal failure groups by 30 to 50% and in normal rats by 20 to 40%. In the presence of CEC, renal nerve stimulation and noradrenaline and methoxamine induced renal vasoconstrictor responses were enhanced (all P<0.05) in the renal failure but not in the normal rats. These data showed that alpha(1A)- and alpha(1D)-adrenoceptors were the major subtypes in mediating adrenergically induced renal vasoconstriction but there was no substantial shift in subtype in renal failure. The contribution of alpha(1B)-adrenoceptor subtypes either pre- or post-synaptic appeared to be raised in the renal failure rats.

Differential effects of peroxynitrite on the function of arginine vasopressin V1a receptors and alpha1-adrenoceptors in vivo

OBJECTIVE

The aim of this study was to provide evidence that peroxynitrite may differentially affect the function of arginine vasopressin (AVP) V(1a) receptors and alpha(1)-adrenoceptors in vascular smooth muscle of the rat

METHODS

The vasoconstrictor responses elicited by AVP, or the alpha(1)-adrenoceptor agonist, phenylephrine, were determined in anesthetized rats before and after injections of (i) peroxynitrite, the thiol chelator, para-hydroxymercurobenzoic acid (PHMBA), or the electron acceptor, nitroblue tetrazolium (NBT). The ability of the reducing agent, glutathione, to reverse the loss of response to phenylephrine and AVP in peroxynitrite-treated rats was also examined.

RESULTS

The AVP-induced responses were suppressed 10-20 min but not 60-70 min after the administration of peroxynitrite. Glutathione reversed the above loss of response to AVP at 10-20 min. The responses elicited by phenylephrine were suppressed 10-20 min and 60-70 min after administration of peroxynitrite. Glutathione did not reverse the above losses of response to phenylephrine. In addition, the vasoconstrictor actions of AVP and phenylephrine were markedly suppressed after administration of PHMBA or nitroblue tetrazolium.

CONCLUSIONS

The above findings provide evidence that exogenously administered peroxynitrite may differentially affect the function of AVP V(1a) receptors and alpha(1)-adrenoceptors in vascular smooth muscle of the rat. The possibility that peroxynitrite impairs AVP V(1a) receptor function by transient oxidation events whereas peroxynitrite impairs alpha(1)-adrenoceptor function by transient oxidation and permanent nitration events will be discussed.

Vascular ?1-adrenoceptors in isolated perfused rat kidney: influence of ageing

1. The present study identifies alpha1-adrenoceptor subtype(s) involved in constrictor responses of the kidney and how ageing influences it. 2. The study was conducted on kidneys from F344BNF1 rats, which unlike F344 or Wistar rats used by many previous investigators do not exhibit glomerulonephritis at advanced age. 3. Noradrenaline (NA) and phenylephrine (PHE) (non-selective alpha1) and A61063 (selective alpha(1A)) adrenoceptor agonists elicited constriction of perfused kidneys of young and old rats. The pD2 values (index of renovascular reactivity) were significantly higher for A61603 than for either PHE or NA, and significantly decrease across age groups. 4. BMY 7378 or RS 100329, alpha(1D)- or alpha(1A)-adrenoceptor antagonists, respectively antagonized the constrictor responses and suppressed the maximal responses to all agonists in young adult rat kidneys. However, antagonism of PHE or A61063 by BMY 7378 in old rat kidneys was surmountable. 5. This study suggests that: (i) alpha(1A) and alpha(1D)-adrenoceptor subtypes mediate vasoconstriction of perfused rat kidney; (ii) alpha(1A)-adrenoceptor subtype appears to predominate in renal vasculature based on agonist relative potencies. (iii) Ageing significantly decreases alpha1-adrenoceptor-mediated vasoconstriction of rat kidney.

Chloroethylclonidine reveals that alpha (1 A)-adrenoceptors mediate contraction in aorta of alpha (1 D)-adrenoceptor knockout mice

1 We have characterized the alpha(1)-adrenoceptor subtypes present in isolated aorta of the alpha(1D)-adrenoceptor knockout (KO) mice, by chloroethylclonidine (CEC)-induced alkylation and their protection by selective alpha(1)-adrenoceptor antagonists. 2 The alpha(1D)-adrenoceptor is involved in the contractile response to noradrenaline in wild type (WT) mouse aorta. 3 In WT mice 5-methylurapidil (5-MU, an alpha(1A)-adrenoceptor antagonist) or BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl] ethyl]-8-azaspiro[4.5] decane-7,9 dione, a selective alpha(1D)-adrenoceptor antagonist), protected the receptors from CEC-induced (alpha(1B/D)-adrenoceptor) alkylation, the combination of both antagonists resulted in complete protection, while AH11110A (1-[biphenyl-2-yloxy]-4-imino-4-piperidin-1-yl-butan-2-ol, an alpha(1B)-adrenoceptor antagonist) did not protect. 4 In aorta of KO mice there was a 19-fold rightward shift in noradrenaline effective concentration (EC(50)) compared with WT; while 5-MU alone or in combination with AH11110A protected alpha(1)-adrenoceptors to the same extent. 5 The data indicate that alpha(1A)-adrenoceptors mediate contraction and suggest their role in maintaining homeostasis in the alpha(1D)-adrenoceptors KO mice.

Selective agonists reveal ?1A- and ?1B-adrenoceptor subtypes in caudal artery of the young rat

Multiple alpha(1)-adrenoceptors were evaluated in caudal artery of the young Wistar rat using selective agonists and antagonists. Arteries were exposed to the selective alpha(1A)-adrenoceptor agonist, A-61603 (N-[5-(4,5-dihydro-1H-imidazol-2-yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl] methanesulfonamide) or to phenylephrine and to prazosin (alpha(1)-adrenoceptor antagonist), or the selective alpha(1A)-adrenoceptor antagonists 5-methylurapidil, RS 100329 (5-methyl-3-[3-[4-[2-(2,2,2,-trifluoroethoxy)phenyl]-1-piperazinyl]propyl]-2,4-(1H)-pyrimidinedione), RS 17053 (N-[2(2-cyclopropylmethoxy) ethyl]-5-chloro-alpha, alpha-dimethyl-1H-indole-3-ethanamide), and the selective alpha(1D)-adrenoceptor antagonist BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5] decane-7,9-dione). Results showed a 100-fold higher potency of A-61603 for the alpha(1)-adrenoceptor present in the artery, compared with phenylephrine. Prazosin displaced both agonists with high affinity, whereas 5-methylurapidil, RS 100329 and RS 17053 displaced A-61603 with high affinity, indicating the presence of alpha(1A)-adrenoceptors. The selective alpha(1A)-adrenoceptor antagonists blocked phenylephrine responses with low affinity, suggesting that phenylephrine activated a second receptor population in caudal artery. BMY 7378 antagonized with low affinity both A-61603 and phenylephrine-induced contractions, indicating absence of alpha(1D)-adrenoceptors in the vessel. The results suggest that functional alpha(1B)-adrenoceptors are present in caudal arteries of the young Wistar rat.

Sympathetic neurotransmission in the rat testicular capsule: functional characterization and identification of mRNA encoding alpha1-adrenoceptor subtypes

The rat testicular capsule is a thin tissue surrounding the testis, whose precise function is still unknown. We have studied the contractile effects of electrical field stimulation, noradrenaline, and the blockade by antagonists of adrenergic receptors, in order to characterize sympathetic neurotransmission, and adrenoceptor subtypes. In addition, reverse transcription polymerase chain reaction (RT-PCR) assays were made to check for the expression of the three known subtypes of alpha(1)-adrenoceptors. The effects of electrical field stimulation (2 to 20 Hz, 1 ms, 60 V) were almost totally abolished by depletion of neuronal noradrenaline storage with reserpine (10 mg/Kg), but not by the purinergic receptor antagonist suramin (10(-5) M), indicating that noradrenaline, but not ATP, was involved in contractions. The selective alpha(1)-adrenoceptor antagonist prazosin (10(-7) M) was more effective than the selective alpha(2)-adrenoceptor antagonist idazoxan (10(-7) M) to inhibit contractions induced by electrical field stimulation, pointing out a major involvement of alpha(1)-adrenoceptor. When noradrenaline was used instead of electrical field stimulation, it showed a high potency (pD(2)=7.9). Noradrenaline-induced contractions were competitively blocked by the selective alpha(1A)-adrenoceptor antagonists WB 4101 (pA(2)=8.88), phentolamine (pA(2)=8.39) and by the alpha(1B)-adrenoceptor antagonist spiperone (pA(2)=8.57), indicating the presence of functional alpha(1A)- and alpha(1B)-adrenoceptors. In addition, contractions were not blocked by the selective alpha(1D)-adrenoceptor antagonist BMY 7378 (up to 10(-6) M), while selective alpha(2)-adrenoceptor antagonists showed low pA(2) values (yohimbine, 7.25 and idazoxan, 7.49), suggesting a minor role, if any, for alpha(1D)- and alpha(2)-adrenoceptors. To check the proportionate role of alpha(1A)- and alpha(1B)-adrenoceptors, we blocked alpha(1B)-adrenoceptors with chloroethylclonidine (CEC, 30 microM, 45 min), that reduced the maximal effect of noradrenaline by about 60%. The remnant CEC-insensitive noradrenaline contraction was assumed to be unrelated to alpha(1B)-adrenoceptor, and was inhibited by 5-methyl-urapidil (pA(2)=8.94) and by the Ca(2+) channel blocker nifedipine (3 microM), confirming the involvement of alpha(1A)-adrenoceptors. The presence of mRNA encoding alpha(1A)- and alpha(1B)-adrenoceptor was also shown on RT-PCR assays. Unexpectedly, alpha(1D)-transcripts were also detected in these assays. Taken together, our results show that ATP co-transmission could not be detected, and that neurotransmission involves the interaction of noradrenaline with both alpha(1A)- and alpha(1B)-, but not with alpha(1D)- or alpha(2)-adrenoceptor. The fact that the functional alpha(1D)-adrenoceptor could not be detected in spite of the presence of the corresponding mRNA, remains to be investigated.

Captopril therapy decreases both expression and function of alpha1D-adrenoceptors in pre- hypertensive rat aorta

1.-- The effects of captopril on alpha(1)-adrenoceptor mRNA and protein and phenylephrine-induced contraction was assessed in aorta of pre-hypertensive spontaneously hypertensive rats. 2.-- Four-week-old SHR and WKY rats were treated with captopril [an angiotensin-converting enzyme (ACE) inhibitor] 3 mg kg(-1) day(-1) for 1 week. 3.-- pA(2) values for BMY 7378, an alpha(1D)-adrenoceptor antagonist, were 8.63-9.20 among the different groups. Schild slopes were close to unity suggesting that contraction was produced primarily by alpha(1D)-adrenoceptor stimulation and was not changed with therapy. 4.-- Alpha(1D)-adrenoceptor mRNA and protein values were higher in pre-hypertensive SHR than in WKY, whereas alpha(1A)-adrenoceptor mRNA was higher in WKY and alpha(1B)-adrenoceptors were similar in both strains, and protein was not significantly different for alpha(1A)- and alpha(1B)-subtypes. 5.-- Captopril decreased maximal contraction in SHR, without having effect in WKY rats, while alpha(1D)-adrenoceptor mRNA was decreased in both rat strains but alpha(1D)-adrenoceptor protein was significantly decreased only in SHR, and increased alpha(1A)-mRNA in SHR, no effect of captopril treatment was observed on alpha(1B)-adrenoceptor mRNA and protein nor on alpha(1A)-adrenoceptor protein. 6.-- These data suggest that ACE inhibition by captopril influences both expression and function of alpha(1D)-adrenoceptors in aorta of pre-hypertensive rats, probably avoiding alpha(1D)-subtype expression by blockade of angiotensin II synthesis.

The elusive alpha(1D)-adrenoceptor: molecular and cellular characteristics and integrative roles

alpha(1)-Adrenoceptors seem to play key roles in cardiovascular, genitourinary, and central nervous system functions. This review will be focused on alpha(1D)-adrenoceptors. These receptors have intrinsic activity, and many of the more commonly used antagonists are in reality inverse agonists. alpha(1D)-Adrenoceptors are phosphorylated in the basal state, and the natural agonists, adrenaline and noradrenaline, increase their phosphorylation; similar effects are induced by direct activation of protein kinase C and through activation of nonadrenergic receptors. Interestingly, a large proportion of alpha(1D)-adrenoceptors are located in intracellular vesicles. Such intracellular location can be changed to surface expression through the use of inverse agonists and coexpression of alpha(1B)-adrenoceptors, which seem to act as pharmacological chaperons for proper plasma membrane insertion. The alpha(1D)-adrenoceptor amino terminus seems to contain a signal that keeps the receptor intracellularly, but interaction with other proteins may also contribute. The precise relationship between the intrinsic activity, phosphorylation, and intracellular location is currently unknown. alpha(1D)-Adrenoceptor activation induces contraction in a variety of vessels, and a role in the control of blood pressure has been suggested. Studies using young prehypertensive and adult spontaneously hypertensive rats as well as knockout mice suggest that vascular alpha(1D)-adrenoceptors are involved in the genesis/maintenance of hypertension.

Correlation between mRNA levels and functional role of alpha1-adrenoceptor subtypes in arteries: evidence of alpha1L as a functional isoform of the alpha1A-adrenoceptor

The mRNA levels for the three alpha1-adrenoceptor subtypes, alpha1A, alpha1B, and alpha1D, were quantified by real-time RT-PCR in arteries from Wistar rats. The alpha1D-adrenoceptor was prominent in both aorta (79.0%) and mesenteric artery (68.7%), alpha1A predominated in tail (61.7%) and small mesenteric artery (73.3%), and both alpha1A- and alpha1D-subtypes were expressed at similar levels in iliac artery. The mRNA levels of the alpha1B-subtype were a minority in all vessels (1.7-11.1%). Concentration-response curves of contraction in response to phenylephrine or relaxation in response to alpha1-adrenoceptor antagonists on maximal sustained contraction induced by phenylephrine were constructed from control vessels and vessels pretreated with 100 micromol/l chloroethylclonidine (CEC) for 30 min. The significant decrease in the phenylephrine potency observed after CEC treatment together with the inhibitory potency displayed by 8-{2-[4-(2-methoxyphenyl)-1-piperazinyl]-8-azaspiro (4,5) decane-7-dionedihydrochloride} (BMY-7378, an alpha1D-adrenoceptor antagonist) confirm the relevant role of alpha1D-adrenoceptors in aorta and iliac and proximal mesenteric arteries. The potency of 5-methylurapidil (an alpha1A-adrenoceptor antagonist) and the changes in the potency of both BMY-7378 and 5-methylurapidil after CEC treatment provided evidence of a mixed population of alpha1A- and alpha1D-adrenoceptors in iliac and distal mesenteric arteries. The low potency of prazosin (pIC50 < 9) as well as the high 5-methylurapidil potency in tail and small mesenteric arteries suggest the main role of alpha1A/alpha1L-adrenoceptors with minor participation of the alpha1D-subtype. The mRNA levels and CEC treatment corroborated this pattern and confirmed that the alpha1L-adrenoceptor could be a functional isoform of the alpha1A-subtype.

The contribution of adrenoceptor subtype(s) in the renal vasculature of diabetic spontaneously hypertensive rats

1. Diabetes and hypertension are both associated with an increased risk of renal disease and are associated with neuropathies, which can cause defective autonomic control of major organs including the kidney. This study aimed to examine the alpha(1)-adrenoceptor subtype(s) involved in mediating adrenergically induced renal vasoconstriction in a rat model of diabetes and hypertension. 2. Male spontaneously hypertensive rats (SHR), 220-280 g, were anaesthetized with sodium pentobarbitone 7-day poststreptozotocin (55 mg x kg(-1) i.p.) treatment. The reductions in renal blood flow (RBF) induced by increasing frequencies of electrical renal nerve stimulation (RNS), close intrarenal bolus doses of noradrenaline (NA), phenylephrine (PE) or methoxamine were determined before and after administration of nitrendipine (Nit), 5-methylurapidil (5-MeU), chloroethylclonidine (CEC) and BMY 7378. 3. In the nondiabetic SHR group, mean arterial pressure (MAP) was 146+/-6 mmHg, RBF was 28.0+/-1.4 ml x min(-1) x kg(-1) and blood glucose was 112.3+/-4.7 mg x dl(-1), and in the diabetic SHR Group, MAP was 144+/-3 mmHg, RBF 26.9+/-1.3 ml(-1) min x kg(-1) and blood glucose 316.2+/-10.5 mg x dl(-1). Nit, 5-MeU and BMY 7378 blunted all the adrenergically induced renal vasoconstrictor responses in SHR and diabetic SHR by 25-35% (all P<0.05), but in diabetic rats the responses induced by RNS and NA treated with 5-MeU were not changed. By contrast, during the administration of CEC, vasoconstrictor responses to all agonists were enhanced by 20-25% (all P<0.05) in both the SHR and diabetic SHR. 4. These findings suggest that alpha(1A) and alpha(1D)-adrenoceptor subtypes contribute in mediating the adrenergically induced constriction of the renal vasculature in both the SHR and diabetic SHR. There was also an indication of a greater contribution of presynaptic adrenoceptors, that is, alpha(1B)-, and/or alpha(2)-subtypes.

Pharmacological characterization of alpha1-adrenoceptor subtypes in the bovine tail artery

Ioudina, M. V., Dyer, D. C. Pharmacological characterization of alpha1-adrenoceptor subtypes in the bovine tail artery. J. vet. Pharmacol. Therap. 25, 363-369. The purpose of this study was to identify the alpha1-adrenoreceptor subtypes present in the bovine tail artery which mediate contractions to adrenergic agonists. A61603, an alpha1A-selective agonist, was more potent compared with norepinephrine and phenylephrine. The pKA value of A61603 was 6.93 +/- 0.19 microM (n=6). Antagonists, BMY 7378, WB 4101 and 5-methylurapidil, caused a parallel shift to the right of the concentration-response curve to A61603 with pA2 values of 6.62, 9.27 and 8.86, respectively. Prazosin, BMY 7378 and WB 4101 inhibited phenylephrine induced contraction with pA2 values of 9.47, 7.17 and 9.73, respectively. The pA2 values obtained for 5-methylurapidil, WB 4101, BMY 7378 and prazosin against alpha1-adrenoceptor agonists were significantly correlated with pKi values (Zhu, Zhang & Han, 1997, Eur. J. Pharmacol.329, 55-61) for the cloned alpha1a-adrenoceptor but not with the cloned alpha1b- or alpha1d-adrenoceptor. BMY 7378, a selective alpha1D-adrenoceptor antagonist, was significantly more potent against the nonsubtype selective agonist phenylephrine than to A61603. Chloroethylclonidine (50 microM for 10 min) did not affect contractile responses to A61603, but caused a significant inhibition of contractile responses to phenylephrine. In conclusion, it appears that alpha1A- and alpha1D-adrenoceptors play a role in adrenergic mediated contraction in the bovine tail artery.

Transgenic studies of alpha(1)-adrenergic receptor subtype function

Mice with altered alpha(1)-adrenergic receptor (AR) genes have become important tools in elucidating the subtype-specific functions of the three alpha(1)-AR subtypes because of the lack of sufficiently subtype-selective pharmacological agents. Mice with a deletion (knockout, KO) or an overexpression (transgenic, TG) of the alpha(1A)-, alpha(1B)-, or alpha(1D)-AR subtypes have been generated. The alpha(1)-ARs are the principal mediators of the hypertensive response to alpha(1)-agonists in the cardiovascular system. Studies with these mice indicate that alpha(1A)-AR and alpha(1B)-AR subtypes play an important role in cardiac development and/or function as well as in blood pressure (BP) response to alpha(1)-agonists via vasoconstriction. The alpha(1B)- and alpha(1D)-subtypes also appear to be involved in central nervous system (CNS) processes such as nociceptive responses, modulation of memory consolidation and working memory. The ability to study subtype-specific functions in different mouse strains by altering the same alpha(1)-AR in different ways strengthens the conclusions drawn from these studies. Although these genetic approaches have limitations, they have significantly increased our understanding of the functions of alpha(1)-AR subtypes.

Role of the alpha1D-adrenergic receptor in the development of salt-induced hypertension

In an attempt to elucidate whether there is a specific alpha1-adrenergic receptor (alpha1-AR) subtype involved in the genesis or maintenance of hypertension, the alpha1D-AR subtype was evaluated in a model of salt-induced hypertension. The alpha1D-AR-deficient (alpha1D-/-) and control (alpha1D+/+) mice (n=8 to 14 in each group) were submitted to subtotal nephrectomy and given 1% saline as drinking water for 35 days. Blood pressure (BP) was monitored by tail-cuff readings and confirmed at the end point by direct intraarterial BP recording. The alpha1D-/- mice had a significantly (P=0.0004) attenuated increase in BP response in this protocol (baseline 94.6+/-2.8 versus end point 107.4+/-4.5 mm Hg) compared with that of their wild-type counterparts (alpha1D+/+), from a baseline 97.4+/-2.9 to an end point 139.4+/-4.5 mm Hg. Seven of 15 alpha1D+/+ mice died with edema, probably owing to renal failure, whereas 14 of 15 alpha1D-/- mice were maintained for 35 days. Body weight, renal remnant weight, and residual renal function were similar in the 2 groups, whereas the values of plasma catecholamines (epinephrine, norepinephrine, and dopamine) were higher in alpha1D+/+ than in the alpha1D-/- mice. These data suggest that alpha1D-AR plays an important role in developing a high BP in response to dietary salt-loading, and that agents having selective alpha1D-AR antagonism could have significant therapeutic potential in the treatment of hypertension.

Functional characterization of serotonin receptors in rat isolated aorta

Interactions of serotonin (5-HT) with different specific 5-HT receptors that can coexist in the same blood vessel sometimes generate opposite effects. The aim of this study was to characterize the functional role of previously described mRNAs for 5-HT receptors in the rat aorta (5-HT(2A), 5-HT(2B), 5-HT(1B), 5-HT(7)) as well as to study the known 5-HT(2A) receptor-mediated constrictor response and investigate the influences of endothelium and preconstriction on the tissue in that response. A slight endothelium- and concentration-dependent relaxant effect was observed for 5-HT in aorta precontracted with either 5 microM phenylephrine (PE) or 1 microM prostaglandin F2alpha (PGF2alpha) in the presence of 0.3 microM ketanserin. EC50 values for 5-HT and alpha-methyl-5-HT relaxant responses after PE were 43.10 +/- 4.00 and 57.11 +/- 8.01 nM, respectively. pK(B) values for antagonists cyproheptadine and rauwolscine were 8.92 +/- 0.22 and 7.15 +/- 0.12, respectively. In nonprecontracted tissues, the contractile potency of 5-HT was higher in the absence of endothelium (EC50, degreesM): 2.60 +/- 0.28 and 4.12 +/- 0.21 in the absence and in the presence of endothelium, respectively. The differences were statistically significant (p<0.05). In precontracted tissues, the differences in EC50 values (2.22 +/- 0.40 and 4.65 +/- 0.60 microM without and with endothelium, respectively) were also statistically significant (p<0.05). pK(B) values for the 5-HT(2A) antagonist ketanserin were similar under all conditions tested. In conclusion, under our experimental conditions there are two functional 5-HT receptors in rat aorta: 5-HT(2A) contractile receptor in smooth muscle and a high-affinity relaxant receptor that mediates a very slight response and the pharmacology of which could be compatible with an endothelial 5-HT(2B) receptor.

Alpha-adrenoceptor subtypes

Different studies have led to our present knowledge of the membrane receptors responsible for mediating the responses to the endogenous catecholamines. These receptors were initially differentiated into alpha - and beta-adrenoceptors. Alpha-adrenoceptors mediate most excitatory functions, and were in turn differentiated in the 1970s into alpha(1)- and alpha(2)-adrenoceptors. The alpha(1)-adrenoceptor type usually mediates responses in the effector organ. The alpha(2)-adrenoceptor type is located presynaptically and regulates the release of the neurotransmitter but it is also present in postsynaptical locations. Both alpha-adrenoceptors are important for the control of vascular tone, but we now know that neither alpha(1)- nor alpha(2)-adrenoceptors constitute homogeneous groups. Each alpha-adrenoceptor type can be subdivided into different subtypes and in this review we have turned our attention to these. The alpha(1)- and the alpha(2)-adrenoceptor subtypes were previously defined pharmacologically by functional and binding studies, and later they were also isolated and identified using cloning methods. In fact, the study of alpha-adrenoceptors was revolutionized by the techniques of molecular biology which permitted us to establish the present classification. The present classification of alpha(1)-adrenoceptors stands as follows: alpha(1A)-adrenoceptor subtype (cloned alpha(1c) and redesignated alpha(1a/c)), alpha(1B)-adrenoceptor subtype (cloned alpha(1b)) and alpha(1D)-adrenoceptor subtype (cloned alpha(1d) and redesignated alpha(1a/d)). It has not been easy to establish the distribution of these alpha(1)-adrenoceptor subtypes in the various organs and tissues, or to define the functional response mediated by each one in the different species studied. Nevertheless it seems that the alpha(1A)-adrenoceptor subtype is more implicated in the maintenance of vascular basal tone and of arterial blood pressure in conscious animals, and the alpha(1B)-adrenoceptor subtype participates more in responses to exogenous agonists. It has also been observed that the expression of the alpha(1B)-adrenoceptor subtype can be modified in pathological situations and particular attention has been paid to the regulation of expression of this receptor. The present classification of alpha(2)-adrenoceptors stands as follows: alpha(2A/D)-adrenoceptor subtype (today it is accepted that the alpha(2A)-adrenoceptor subtype and the alpha(2D)-adrenoceptor subtype are the same receptor but they were identified in different species: the alpha(2A) in human and the alpha(2D) in rat); alpha(2B)-adrenoceptor subtype (cloned alpha(2b)) and alpha(2C)-adrenoceptor subtype (cloned alpha(2c)). Today we know that the alpha(2A/D)- and alpha(2B)-adrenoceptor subtypes in particular control arterial contraction, and that the alpha(2C)-adrenoceptor subtype is responsible above all for venous vasoconstriction. We also know that the alpha(2 A/D)-adrenoceptor subtype fundamentally mediates the central effects of the alpha(2)-adrenoceptor agonists. Despite the validity of the above-mentioned classification of the alpha(1)- and alpha(2)-adrenoceptors, it seems clear that the contractions of a large number of tissues including smooth muscle are mediated by more than one alpha-adrenoceptor subtype. Moreover, few ligands recognise only one alpha-adrenoceptor subtype and the lack of specifity in the different drugs for each one limits their administration in vivo and their therapeutic use.

Alpha1-adrenoceptor subtypes on rat afferent arterioles assessed by radioligand binding and RT-PCR

We utilized [3H]prazosin saturation and competition radioligand binding studies to characterize the expression of alpha1-adrenoceptors in preglomerular vessels. mRNA for adrenoceptor subtypes was assayed using RT-PCR. The vessels were isolated using an iron oxide-sieving method. [3H]prazosin bound to a single class of binding sites (Kd 0.087 +/- 0.012 nM, Bmax 326 +/- 56 fmol/mg protein). Phentolamine displaced [3H]prazosin (0.2 nM) with a pK(i) of 8.37 +/- 0.09. Competition with the selective alpha1A-adrenoceptor antagonist 5-methylurapidil fit a two-site model (pK(i) 9.38 +/- 0.21 and 7.04 +/- 0.15); 59 +/- 3% of the sites were high-affinity, and 41 +/- 3% were low-affinity binding sites. Competition with the alpha1D-adrenoceptor antagonist 8-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-8-azaspiro[4.5]decane-7,9-dione dihydrochloride (BMY-7378) fit a one-site model with low affinity (pK(i) 6.83 +/- 0.03). The relative contents of alpha1A-, alpha1B-, and alpha1D-adrenoceptor mRNAs were 64 +/- 5, 25 +/- 5, and 11 +/- 1%, respectively. Thus there was a very good correlation between mRNA and receptor binding for the subtypes. These data indicate a predominance of the alpha1A-adrenoceptor subtype in rat renal resistance vessels, with smaller densities of alpha1B- and alpha1D-adrenoceptors.

The role of several alpha(1)- and alpha(2)-adrenoceptor subtypes mediating vasoconstriction in the canine external carotid circulation

1. It has recently been shown that both alpha(1)- and alpha(2)-adrenoceptors mediate vasoconstriction in the canine external carotid circulation. The present study set out to identify the specific subtypes (alpha(1A), alpha(1B) and alpha(1D) as well as alpha(2A), alpha(2B) and alpha(2C)) mediating the above response. 2. Consecutive 1 min intracarotid infusions of phenylephrine (alpha(1)-adrenoceptor agonist) and BHT933 (alpha(2)-adrenoceptor agonist) produced dose-dependent decreases in external carotid blood flow, without affecting mean arterial blood pressure or heart rate. 3. The responses to phenylephrine were selectively antagonized by the antagonists, 5-methylurapidil (alpha(1A)) or BMY7378 (alpha(1D)), but not by L-765,314 (alpha(1B)), BRL44408 (alpha(2A)), imiloxan (alpha(2B)) or MK912 (alpha(2C)). In contrast, only BRL44408 or MK912 affected the responses to BHT933. 4. The above results support our contention that mainly the alpha(1A), alpha(1D), alpha(2A) and alpha(2C)-adrenoceptor subtypes mediate vasoconstriction in the canine external carotid circulation.

Phosphorylation and desensitization of alpha1d-adrenergic receptors

In rat-1 fibroblasts stably expressing rat alpha(1d)-adrenoceptors, noradrenaline and PMA markedly decreased alpha(1d)-adrenoceptor function (noradrenaline-elicited increases in calcium in whole cells and [(35)S]guanosine 5'-[gamma-thio]triphosphate binding in membranes), suggesting homologous and heterologous desensitizations. Photoaffinity labelling, Western blotting and immunoprecipitation identified alpha(1d)-adrenoceptors as a broad band of 70-80 kDa. alpha(1d)-Adrenoceptors were phosphorylated in the basal state and noradrenaline and PMA increased it. The effect of noradrenaline was concentration-dependent (EC(50) 75 nM), rapid (maximum at 1 min) and transient. Phorbol ester-induced phosphorylation was concentration-dependent (EC(50) 25 nM), slightly slower (maximum at 5 min) and stable for at least 60 min. Inhibitors of protein kinase C decreased the effect of phorbol esters but not that of noradrenaline. Evidence of cross-talk of alpha(1d)-adrenoceptors with receptors endogenously expressed in rat-1 fibroblasts was given by the ability of endothelin, lysophosphatidic acid and bradykinin to induce alpha(1d)-adrenoceptor phosphorylation. In summary, it is shown for the first time here that alpha(1d)-adrenoceptors are phosphoproteins and that receptor phosphorylation is increased by the natural ligand, noradrenaline, by direct activation of protein kinase C and via cross-talk with other receptors endogenously expressed in rat-1 fibroblasts. Receptor phosphorylation has functional repercussions.

Alpha 1-adrenergic receptor regulation: basic science and clinical implications

Adrenergic receptors (ARs) are members of the G-protein-coupled receptor family, which includes alpha 1ARs, alpha 2ARs, beta 1ARs, beta 2ARs, beta 3ARs, adenosine, muscarinic, angiotensin, endothelin receptors, and many others that are responsible for a large variety of physiologic effects through G-protein coupling. This review focuses on alpha 1ARs and their regulation at both the mRNA and protein levels. Currently, three alpha 1AR subtypes have been characterized both pharmacologically and at the gene level: alpha 1aAR, alpha 1bAR, and alpha 1dAR. These are expressed in a species- and tissue-dependent manner. Mutagenesis approaches have been extremely valuable in the identification of key residues that govern alpha 1AR ligand binding and signaling. These studies reveal that alpha 1ARs have evolved an exquisitely sensitive regulation of their activity in which any disruption of the native structure has profound effects on subsequent function and effector coupling. Significant advances have also been made in the elucidation of signaling pathway components, resulting in the identification of novel pathways that can lead to pathologic conditions. Specific topics include mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and G-protein-coupled receptor cross-talk pathways. Within this context, recent studies identifying underlying transcriptional mechanisms involved in the regulation of the alpha 1AR subtypes are also discussed. Finally, given the potentially important role of alpha 1ARs in the vasculature, as well as in the pathology of many diseases, such as myocardial hypertrophy and benign prostatic hyperplasia, the clinical relevance of alpha 1AR distribution, pharmacology, and therapeutic intervention is reviewed.

Alpha(1)-adrenoceptor subtypes mediating contractions of the rat mesenteric artery

The alpha(1)-adrenoceptor subtype(s) mediating contractions of the rat mesenteric artery were investigated using the agonists methoxamine, cirazoline, P7480 (N-(4-pyridinyl)-1H-indol-1-amine) and subtype-selective antagonists including BMY 7378 (8-(-2(-4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-8-azaspiro(4, 5)decane-7,9,dione dihydrochloride). pA(2) or apparent pK(B) values of antagonists against methoxamine contractions correlated best with its pK(i) values at the cloned alpha(1b)-(0.88), with cirazoline, antagonists affinities correlated equally well with those at alpha(1a)-(0.79) or the alpha(1b)-(0.81) while with P7480 antagonist affinities correlated best with the alpha(1d)-adrenoceptor subtype (0.94). The low affinity estimate for 5-methylurapidil (7.5) against the alpha(1a)-selective cirazoline suggests an alpha(1A)-subtype mediating contraction is unlikely. Shallow Schild plot slopes of subtype selective antagonists against all three agonists are consistent with heterogeneity of alpha(1)-adrenoceptors. P7480 (putative alpha(1D)-adrenoceptor-selective) acts primarily at this subtype and at another which is more likely to be an alpha(1B)- than an alpha(1A)-adrenoceptor. The results with both agonists and antagonists are consistent with contractions of the rat mesenteric artery being mediated via the alpha(1D)- and possibly alpha(1B)-adrenoceptor.

alpha(1)-adrenoceptor subtypes in rat renal resistance vessels: in vivo and in vitro studies

This study provides new information about the relative importance of different alpha(1)-adrenoceptors during norepinephrine (NE) activation in rat renal resistance vessels. In Sprague-Dawley rats, we measured renal blood flow (RBF) using electromagnetic flowmetry in vivo and the intracellular free calcium concentration ([Ca(2+)](i)) utilizing ratiometric photometry of fura 2 fluorescence in isolated afferent arterioles. Renal arterial bolus injection of NE produced a transient 46% decrease in RBF. In microdissected afferent arterioles, NE (1 microM) elicited an immediate square-shaped increase in [Ca(2+)](i), from 90 to 175 nM (P < 0.001). Chloroethylclonidine (CEC) (50 microM) had no chronic irreversible alkylating effect in vitro but exerted acute reversible blockade on norepinephrine (NE) responses both on [Ca(2+)](i) in vitro and on RBF in vivo. The RBF response was attenuated by approximately 50% by the putative alpha(1A)-adrenoceptor and alpha(1D)-adrenoceptor antagonists 5-methylurapidil (5-MU), and 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4. 5]decane-7,9-dione dihydrochloride (BMY-7378) (12.5 and 62.5 microg/h), respectively. The in vitro [Ca(2+)](i) response to NE was blocked approximately 25% and 50% by 5-MU (100 nM and 1 microM). BMY-7378 (100 nM and 1 microM) attenuated the NE-induced response by approximately 40% and 100%. The degree of inhibition in vitro was similar to the in vivo experiments. In conclusion, 5-MU and BMY-7378 attenuated the NE-induced responses, although relatively high concentrations were required, suggesting involvement of both the alpha(1A)-adrenoceptor and alpha(1D)-adrenoceptor. Participation of the alpha(1B)-adrenoceptor is less likely, as we found no evidence for CEC-induced alkylation.

Alpha 1-adrenoceptors: subtypes, signaling, and roles in health and disease

Alpha 1-adrenoceptors mediate some of the main actions of the natural catecholamines, adrenaline, and noradrenaline. They participate in many essential physiological processes, such as sympathetic neurotransmission, modulation of hepatic metabolism, control of vascular tone, cardiac contraction, and the regulation of smooth muscle activity in the genitourinary system. It is now clear that alpha 1-adrenoceptors mediate, in addition to immediate effects, longer term actions of catecholamines such as cell growth and proliferation. In fact, adrenoceptor genes can be considered as protooncogenes. Over the past years, considerable progress has been achieved in the molecular characterization of different alpha 1-adrenoceptor subtypes. Three main subtypes have been characterized pharmacologically and in molecular terms. Splice variants, truncated isoforms, and polymorphisms have also been detected. Similarly, it is now clear that these receptors are coupled to several classes of G proteins that, therefore, are capable of modulating different signaling pathways. In the present article, some of these aspects are reviewed, together with the distribution of the subtypes in different tissues and some of the known roles of these receptors in health and disease.

Vascular alpha 1D-adrenoceptors: are they related to hypertension?

Heterogeneity of vascular alpha 1-adrenoceptor subtypes has been revealed by pharmacological and molecular biology studies (i.e., alpha 1A-, alpha 1B-, and alpha 1D-adrenoceptors). The alpha 1D-adrenoceptor subtype is predominantly involved in the contraction of a variety of vessels and its role in the control of blood pressure has been suggested, a phenomenon probably related to aging. Recent advances in the use of young pre-hypertensive rats and adult spontaneously hypertensive rats with one kidney and Grollman-type renal hypertension suggest vascular alpha 1D-adrenoceptor involvement in the increased blood pressure. The possible role of alpha 1D-adrenoceptors in the genesis/maintenance of hypertension is discussed in this review.

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.

Subtypes of functional alpha1- and alpha2-adrenoceptors

In this review, subtypes of functional alpha1- and alpha2-adrenoceptors are discussed. These are cell membrane receptors, belonging to the seven transmembrane spanning G-protein-linked family of receptors, which respond to the physiological agonists noradrenaline and adrenaline. Alpha1-adrenoceptors can be divided into alpha1A-, alpha1B- and alpha1D-adrenoceptors, all of which mediate contractile responses involving Gq/11 and inositol phosphate turnover. A 4th alpha1-adrenoceptor, the alpha1L-, has been postulated to mediate contractions in some tissues, but its relationship to cloned receptors remains to be established. Alpha2-adrenoceptors can be divided into alpha2A-, alpha2B- and alpha2C-adrenoceptors, all of which mediate contractile responses. Prejunctional inhibitory alpha2-adrenoceptors are predominantly of the alpha2A-adrenoceptor subtype (the alpha2D-adrenoceptor is a species orthologue), although alpha2C-adrenoceptors may also occur prejunctionally. Although alpha2-adrenoceptors are linked to inhibition of adenylate cyclase, this may not be the primary signal in causing smooth muscle contraction; likewise, prejunctional inhibitory actions probably involve restriction of Ca2+ entry or opening of K+ channels. Receptor knock-out mice are beginning to refine our knowledge of the functions of alpha-adrenoceptor subtypes.