Role of the alpha2B-adrenergic receptor in the development of salt-induced hypertension

Designing Chromane Derivatives as α2A-Adrenoceptor Selective Agonists via Conformation Constraint

Enhancing the selectivity of alpha2-adrenoceptor (α2A-AR) agonists remains an unresolved issue. Herein, we reported the design of an α2A-AR agonist using the conformation constraint method, beginning with medetomidine. The structure-activity relationship indicated that the 8-substituent of chromane derivatives exerted the most pronounced effect on α2A-AR agonistic activity. Compounds A9 and B9 were identified as the most promising, exhibiting EC50 values of 0.78 and 0.23 nM, respectively. Their selectivity indexes surpassed dexmedetomidine (DMED) by 10-80 fold. In vivo studies demonstrated that both A9 and B9 dose-dependently increased the loss of righting reflex in mice, with ED50 values of 1.54 and 0.138 mg/kg, respectively. Binding mode calculations and mutation studies suggested the indispensability of the hydrogen bond between ASP1283.32 and α2A-AR agonist. In particular, A9 and B9 showed no dual reverse pharmacological effect, a characteristic exhibited by DMED in α2A-AR activation.

The Discovery of Novel α2a Adrenergic Receptor Agonists Only Coupling to Gαi/O Proteins by Virtual Screening

Most α2-AR agonists derived from dexmedetomidine have few structural differences between them and have no selectivity for α2A/2B-AR or Gi/Gs, which can lead to side effects in drugs. To obtain novel and potent α2A-AR agonists, we performed virtual screening for human α2A-AR and α2B-AR to find α2A-AR agonists with higher selectivity. Compound P300-2342 and its three analogs significantly decreased the locomotor activity of mice (p < 0.05). Furthermore, P300-2342 and its three analogs inhibited the binding of [3H] Rauwolscine with IC50 values of 7.72 ± 0.76 and 12.23 ± 0.11 μM, respectively, to α2A-AR and α2B-AR. In α2A-AR-HEK293 cells, P300-2342 decreased forskolin-stimulated cAMP production without increasing cAMP production, which indicated that P300-2342 activated α2A-AR with coupling to the Gαi/o pathway but without Gαs coupling. P300-2342 exhibited no agonist but slight antagonist activities in α2B-AR. Similar results were obtained for the analogs of P300-2342. The docking results showed that P300-2342 formed π-hydrogen bonds with Y394, V114 in α2A-AR, and V93 in α2B-AR. Three analogs of P300-2342 formed several π-hydrogen bonds with V114, Y196, F390 in α2A-AR, and V93 in α2B-AR. We believe that these molecules can serve as leads for the further optimization of α2A-AR agonists with potentially few side effects.

Subcellular distribution of α2-adrenoceptor subtypes in the rodent kidney

Renal α2-adrenoceptors have been reported to play a role in the regulation of urinary output, renin secretion, and water and sodium excretion in the kidneys. However, the distribution of α2-adrenoceptor subtypes in the kidneys remains unclear. In this study, we aimed to investigate the localization of α2-adrenoceptor subtypes in rat kidneys using 8-week-old Sprague-Dawley rats. Immunofluorescence imaging revealed that both α2A- and α2B-adrenoceptors were expressed in the basolateral, but not apical, membrane of the epithelial cells of the proximal tubules. We also found that α2A- and α2B-adrenoceptors were not expressed in the glomeruli, collecting ducts, or the descending limb of the loop of Henle and vasa recta. In contrast, α2C-adrenoceptors were found to be localized in the glomeruli and lumen of the cortical and medullary collecting ducts. These results suggest that noradrenaline may act on the basement membrane of the proximal tubules through α2A- and α2B-adrenoceptors. Moreover, noradrenaline may be involved in the regulation of glomerular filtration and proteinuria through the induction of morphological changes in mesangial cells and podocytes via α2C-adrenoceptors. In the collecting ducts, urinary noradrenaline may regulate morphological changes of the microvilli through α2C-adrenoceptors. Our findings provide an immunohistochemical basis for understanding the cellular targets of α2-adrenergic regulation in the kidneys. This may be used to devise therapeutic strategies targeting α2-adrenoceptors.

Transgenic Mice Overexpressing Human Alpha-1 Antitrypsin Exhibit Low Blood Pressure and Altered Epithelial Transport Mechanisms in the Inactive and Active Cycles

Human alpha-1 antitrypsin (hAAT) is a versatile protease inhibitor, but little is known about its targets in the aldosterone-sensitive distal nephron and its role in electrolyte balance and blood pressure control. We analyzed urinary electrolytes, osmolality, and blood pressure from hAAT transgenic (hAAT-Tg) mice and C57B/6 wild-type control mice maintained on either a normal salt or high salt diet. Urinary sodium, potassium, and chloride concentrations as well as urinary osmolality were lower in hAAT-Tg mice maintained on a high salt diet during both the active and inactive cycles. hAAT-Tg mice showed a lower systolic blood pressure compared to C57B6 mice when maintained on a normal salt diet but this was not observed when they were maintained on a high salt diet. Cathepsin B protein activity was less in hAAT-Tg mice compared to wild-type controls. Protein expression of the alpha subunit of the sodium epithelial channel (ENaC) alpha was also reduced in the hAAT-Tg mice. Natriuretic peptide receptor C (NPRC) protein expression in membrane fractions of the kidney cortex was reduced while circulating levels of atrial natriuretic peptide (ANP) were greater in hAAT-Tg mice compared to wild-type controls. This study characterizes the electrolyte and blood pressure phenotype of hAAT-Tg mice during the inactive and active cycles and investigates the mechanism by which ENaC activation is inhibited in part by a mechanism involving decreased cathepsin B activity and increased ANP levels in the systemic circulation.

α-Adrenergic receptor blockade attenuates pressor response during mental stress in young black adults

Black individuals exhibit increased blood pressure (BP) responses to sympathetic stimulation that are associated with an increased risk of hypertension (HTN). We tested the hypothesis that α1 -adrenergic blockade inhibits the increased BP response during and after 45-min stress in young normotensive Black adults, which may be mediated, in part, by dampened vasoconstriction and decreased renal sodium retention. Utilizing a double-masked randomized, crossover study design, 51 normotensive Black adults (31 ± 8 yr) were treated with either a placebo or 1 mg/day of prazosin for 1 week. On the final day of each treatment, hemodynamic measures and urinary sodium excretion (UNaV) were collected before (Rest), during (Stress) and after (Recovery) 45 min of mental stress induced via a competitive video game task. During the Stress period, diastolic BP and total peripheral resistance (TPR) were significantly lower with prazosin compared to placebo (p < .05 for both). Similarly, we observed lower systolic BP, diastolic BP, and TPR during the Recovery period with prazosin versus placebo (p < .05 for both). There was no effect of prazosin on stress-associated UNaV. The change in systolic BP from Rest to Recovery was positively associated with the change in TPR with both treatments (p < .05 for both). In summary, prazosin treatment dampened BP reactivity to 45-min mental stress and lowered post-stress BP over the recovery period, which was linked to reduce TPR in young normotensive Black adults. These results suggest that α1 -adrenergic receptor activity may contribute to BP responses and delayed BP recovery to prolonged mental stress through increased vasoconstriction in Black adults.

Pharmacological screening of a new alpha-2 adrenergic receptor agonist, mafedine, in zebrafish

Pharmacological agents acting at alpha-2 adrenergic receptors are widely used in physiology and neuroscience research. Mounting evidence of their potential utility in clinical and experimental psychopharmacology, necessitates new models and novel model organisms for their screening. Here, we characterize behavioral effects of mafedine (6-oxo-1-phenyl-2- (phenylamino)-1,6-dihydropyrimidine-4-sodium olate), a novel drug with alpha-2 adrenergic receptor agonistic effects, in adult zebrafish (Danio rerio) in the novel tank test of anxiety and activity. Following an acute 20-min exposure, mafedine at 60 mg/L produced a mild psychostimulant action with some anxiogenic-like effects. Repeated acute 20-min/day administration of mafedine for 7 consecutive days at 1, 5 and 10 mg/L had a similar action on fish behavior as an acute exposure to 60 mg/L. Since mafedine demonstrated robust behavioral effects in zebrafish - a sensitive vertebrate aquatic model, it is likely that it may modulate rodent and human behavior as well. Thus, further studies are needed to explore this possibility in detail, and whether it may foster clinical application of mafedine and related alpha-2 adrenergic agents.

Non-Central Influences of α2-Adrenergic and Imidazoline Agonist Interactions in Isolated ardiomyocytes Cardiac Cells

Aim: to investigate the functional interaction of α2-adrenergic and imidazoline receptors recently identified on the sarcolemma of isolated cardiomyocytes for regulation of the intracellular calcium and the production of the signal molecule of nitric oxide (NO).Materials and methods:experiments were performed on isolated left ventricular cardiomyocytes of Wistar rats. Potential-dependent Ca2+-currents were measured from the whole-cell by the patch-clamp method in “perforated-patch” configuration. The intracellular calcium and the production of nitric oxide were estimated from the changes in fluorescence intensity of the Ca2+-specific and NO-sensitive dyes at fluorescent or confocal microscope.Results:It has been shown that α2‑adrenergic and imidazoline receptor agonists inhibit L-type Ca2+-currents by themselves, but their effects do not develop against each other’s background. The blockade of key effector molecules: protein kinase B (Akt kinase) for α2‑adrenergic receptors, and protein kinase C for imidazoline receptors causes the action of agonists to become additive. Both the selective α2‑agonist, guanabenz, and the specific agonist of the first type imidazoline receptors, rilmenidine, show an additional inhibition of Ca2+-currents against the basal background already reduced by the activation of one of the two receptor systems. Wherein rilmenidine increases the level of free  Ca2+in the cytosol, and guanabenz, on the contrary, decreases it. The action of guanabenz does not develop against the background of rilmenidine, although it, in turn, effectively increases the intracellular level of calcium in guanabenz-pretreated cardiac cells. Activation of α2‑adrenergic receptors leads to significant stimulation of the endothelial isoform of NO-synthase, and as a result to an increase in the NO level. Activation of imidazoline receptors itself does not affect NO synthesis but it prevents the production of NO induced by α2‑agonists.Conclusion:obtained data make it possible to formulate a number of useful recommendations for clinical practice, and also to clarify the non-central peripheral effects arising from the activation of α2‑adrenergic or imidazoline systems under conditions of endogenous hyperactivation on of the two systems.

Elevated biomarkers of sympatho-adrenomedullary activity linked to e-waste air pollutant exposure in preschool children

Air pollution is a risk factor for cardiovascular disease (CVD), and cardiovascular regulatory changes in childhood contribute to the development and progression of cardiovascular events at older ages. The aim of the study was to investigate the effect of air pollutant exposure on the child sympatho-adrenomedullary (SAM) system, which plays a vital role in regulating and controlling the cardiovascular system. Two plasma biomarkers (plasma epinephrine and norepinephrine) of SAM activity and heart rate were measured in preschool children (n = 228) living in Guiyu, and native (n = 104) and non-native children (n = 91) living in a reference area (Haojiang) for >1 year. Air pollution data, over the 4-months before the health examination, was also collected. Environmental PM_2.5, PM₁₀, SO₂, NO₂ and CO, plasma norepinephrine and heart rate of the e-waste recycling area were significantly higher than for the non-e-waste recycling area. However, there was no difference in plasma norepinephrine and heart rate between native children living in the non-e-waste recycling area and non-native children living in the non-e-waste recycling area. PM_2.5, PM₁₀, SO₂ and NO₂ data, over the 30-day and the 4-month average of pollution before the health examination, showed a positive association with plasma norepinephrine level. PM_2.5, PM₁₀, SO₂, NO₂ and CO concentrations, over the 24 h of the day of the health examination, the 3 previous 24-hour periods before the health examination, and the 24 h after the health examination, were related to increase in heart rate. At the same time, plasma norepinephrine and heart rate on children in the high air pollution level group (≤50-m radius of family-run workshops) were higher than those in the low air pollution level group. Our results suggest that air pollution exposure in e-waste recycling areas could result in an increase in heart rate and plasma norepinephrine, implying e-waste air pollutant exposure impairs the SAM system in children.

Spinophilin Is Indispensable for the α2B Adrenergic Receptor-Elicited Hypertensive Response

The α₂ adrenergic receptor (AR) subtypes are important for blood pressure control. When activated, the α_2A subtype elicits a hypotensive response whereas the α_2B subtype mediates a hypertensive effect that counteracts the hypotensive response by the α_2A subtype. We have previously shown that spinophilin attenuates the α_2AAR-dependent hypotensive response; in spinophilin null mice, this response is highly potentiated. In this study, we demonstrate that spinophilin impedes arrestin-dependent phosphorylation and desensitization of the α_2BAR subtype by competing against arrestin binding to this receptor subtype. The Del301-303 α_2BAR, a human variation that shows impaired phosphorylation and desensitization and is linked to hypertension in certain populations, exhibits preferential interaction with spinophilin over arrestin. Furthermore, Del301-303 α_2BAR-induced ERK signaling is quickly desensitized in cells without spinophilin expression, showing a profile similar to that induced by the wild type receptor in these cells. Together, these data suggest a critical role of spinophilin in sustaining α_2BAR signaling. Consistent with this notion, our in vivo study reveals that the α_2BAR-elicited hypertensive response is diminished in spinophilin deficient mice. In arrestin 3 deficient mice, where the receptor has a stronger binding to spinophilin, the same hypertensive response is enhanced. These data suggest that interaction with spinophilin is indispensable for the α_2BAR to elicit the hypertensive response. This is opposite of the negative role of spinophilin in regulating α_2AAR-mediated hypotensive response, suggesting that spinophilin regulation of these closely related receptor subtypes can result in distinct functional outcomes in vivo. Thus, spinophilin may represent a useful therapeutic target for treatment of hypertension.

Long-term exposure to concentrated ambient PM2.5 increases mouse blood pressure through abnormal activation of the sympathetic nervous system: a role for hypothalamic inflammation

BACKGROUND

Exposure to particulate matter≤2.5 μm in diameter (PM2.5) increases blood pressure (BP) in humans and animal models. Abnormal activation of the sympathetic nervous system may have a role in the acute BP response to PM2.5 exposure. The mechanisms responsible for sympathetic nervous system activation and its role in chronic sustenance of hypertension in response to PM2.5 exposure are currently unknown.

OBJECTIVES

We investigated whether central nervous system inflammation may be implicated in chronic PM2.5 exposure-induced increases in BP and sympathetic nervous system activation.

METHODS

C57BL/6J mice were exposed to concentrated ambient PM2.5 (CAPs) for 6 months, and we analyzed BP using radioactive telemetric transmitters. We assessed sympathetic tone by measuring low-frequency BP variability (LF-BPV) and urinary norepinephrine excretion. We also tested the effects of acute pharmacologic inhibitors of the sympathetic nervous system and parasympathetic nervous system.

RESULTS

Long-term CAPs exposure significantly increased basal BP, paralleled by increases in LF-BPV and urinary norepinephrine excretion. The increased basal BP was attenuated by the centrally acting α2a agonist guanfacine, suggesting a role of increased sympathetic tone in CAPs exposure-induced hypertension. The increase in sympathetic tone was accompanied by an inflammatory response in the arcuate nucleus of the hypothalamus, evidenced by increased expression of pro-inflammatory genes and inhibitor kappaB kinase (IKK)/nuclear factor-kappaB (NF-κB) pathway activation.

CONCLUSION

Long-term CAPs exposure increases BP through sympathetic nervous system activation, which may involve hypothalamic inflammation.

Plasma Norepinephrine in Hypertensive Rats Reflects α(2)-Adrenoceptor Release Control Only When Re-Uptake is Inhibited

α₂-adrenoceptors (AR) lower central sympathetic output and peripheral catecholamine release, thereby protecting against sympathetic hyperactivity and hypertension. Norepinephrine re-uptake–transporter effectively (NET) removes norepinephrine from the synapse. Overflow to plasma will therefore not reflect release. Here we tested if inhibition of re-uptake allowed presynaptic α₂AR release control to be reflected as differences in norepinephrine overflow in anesthetized hypertensive spontaneously hypertensive rats (SHR) and normotensive rats (WKY). We also tested if α₂AR modulated the experiment-induced epinephrine secretion, and a phenylephrine-induced, α₁-adrenergic vasoconstriction. Blood pressure was recorded through a femoral artery catheter, and cardiac output by ascending aorta flow. After pre-treatment with NET inhibitor (desipramine), and/or α₂AR antagonist (yohimbine, L-659,066) or agonist (clonidine, ST-91), we injected phenylephrine. Arterial blood was sampled 15 min later. Plasma catecholamine concentrations were not influenced by phenylephrine, and therefore reflected effects of pre-treatment. Desipramine and α₂AR antagonist separately had little effect on norepinephrine overflow. Combined, they increased norepinephrine overflow, particularly in SHR. Clonidine, but not ST-91, reduced, and pertussis toxin increased norepinephrine overflow in SHR and epinephrine secretion in both strains. L-659,066 + clonidine (central α₂AR-stimulation) normalized the high blood pressure, heart rate, and vascular tension in SHR. α₂AR antagonists reduced phenylephrine-induced vasoconstriction equally in WKY and SHR. Conclusions: α_2AAR inhibition increased norepinephrine overflow only when re-uptake was blocked, and then with particular efficacy in SHR, possibly due to their high sympathetic tone. α_2AAR inhibited epinephrine secretion, particularly in SHR. α_2AAR supported α₁AR-induced vasoconstriction equally in the two strains. α₂AR malfunctions were therefore not detected in SHR under this basal condition.

'Volume-expanded' hypertension: the effect of fluid overload and the role of the sympathetic nervous system in salt-dependent hypertension

It is widely believed that salt-dependent hypertension is induced and maintained by expansion of intravascular fluid volume resulting from excessive retention of sodium. The purpose of this brief article is to present a series of arguments in support of the thesis that volume overload per se does not raise the arterial blood pressure. Several investigators in the 1960s and 1970s reported that excessive retention of salt - regardless of cause - leads to sympathetic activation mediated by the effects of the Na ion on α(2)-adrenergic receptors located mostly in the brainstem. In recent years, the cloning and characterization of α(2)-adrenergic receptors subtypes permitted differentiation of their hemodynamic effects via use of salt loading of nephrectomized animals submitted to genetic engineering or gene treatment. These studies indicate that sodium alters the balance between the sympathoinhibitory α(2A)-adrenergic receptors and the sympathoexcitatory α(2B)-adrenergic receptors, leading to a hyperadrenergic hypertensive state unrelated to volume overload.

Selective targeting of G-protein-coupled receptor subtypes with venom peptides

The G-protein-coupled receptor (GPCR) family is one of the largest gene superfamilies with approx. 370 members responding to endogenous ligands in humans and a roughly equal amount of receptors sensitive to external stimuli from the surrounding. A number of receptors from this superfamily are well recognized targets for medical treatment of various disease conditions, whereas for many others the potential medical benefit of interference is still obscure. A general problem associated with GPCR research and therapeutics is the insufficient specificity of available ligands to differentiate between closely homologous receptor subtypes. In this context, venom peptides could make a significant contribution to the development of more specific drugs. Venoms from certain animals specialized in biochemical hunting contain a mixture of molecules that are directed towards a variety of membrane proteins. Peptide toxins isolated from these mixtures usually exhibit high specificity for their targets. Muscarinic toxins found from mamba snakes attracted much attention during the 1990s. These are 65-66 amino acid long peptides with a structural three-finger folding similar to the α-neurotoxins and they target the muscarinic acetylcholine receptors in a subtype-selective manner. Recently, several members of the three-finger toxins from mamba snakes as well as conotoxins from marine cone snails have been shown to selectively interact with subtypes of adrenergic receptors. In this review, we will discuss the GPCR-directed peptide toxins found from different venoms and how some of these can be useful in exploring specific roles of receptor subtypes.

α2C-adrenoceptor modulators: a patent review

INTRODUCTION

α2-Adrenoceptors (α2-ARs) are membrane proteins belonging to the superfamily of GPCRs. Detailed studies have shown three different subtypes, namely α2A, α2B and α2C. Although numerous α2-AR ligands exist, only a small set of compounds have shown even a degree of selectivity among the three α2-AR subtypes. Moreover, these compounds suffer from binding to receptor sites outside the α2-AR subfamily. Efforts made to understand the biological significance of each α2-AR subtype have greatly been assisted by genetically engineered mice. The main results obtained suggest that α2C-AR stimulation may represent a therapeutic strategy to get an analgesic response with reduced sedative effects and undesirable changes in blood pressure due to α2A-AR activation.

AREAS COVERED

This review summarizes the patent literature about the development of α2C-AR modulators from 2000 to early 2010 and their therapeutic effects evoked by the interaction with this receptor subtype.

EXPERT OPINION

Over 90 patents have been deposited in the last 10 years regarding different methods of α2C-AR modulation (use of agonists or antagonists, nucleic acids and polypeptides) for diagnosis, prognosis and treatment of disorders involving this receptor. Nevertheless, despite the numerous published patents, ligands highly selective for the α2C-AR subtype, which continues to be enigmatic, are lacking.

Resting sympathetic nerve activity is related to age, sex and arterial pressure but not to α2-adrenergic receptor subtype

OBJECTIVE

Sympathetic nerve hyperactivity has been associated with hypertension and heart failure and their cardiovascular complications. The α2-adrenergic receptors have been proposed to play a prominent role in the control of sympathetic neural output, and their malfunction to constitute a potential central mechanism for sympathetic hyperactivity of essential hypertension. Reports on the relationship between variant alleles of α2-adrenergic receptor subtypes and sympathetic drive or its effects, however, have not been consistent. Therefore, this study was planned to test the hypothesis that variant alleles of subtypes of α2-adrenergic receptors are associated with raised muscle sympathetic nerve activity (MSNA) in man.

METHODS

One hundred and seventy-two individuals, with a wide range of arterial pressure, were prospectively examined. Resting MSNA was quantified from multiunit bursts and from single units, and α2-adrenergic receptor subtypes were genotyped from DNA extracted from leucocytes and quantified by spectrophotometry.

RESULTS

No significant relationships between variant alleles of any of the α2A, α2B or α2C subtypes and raised muscle sympathetic activity were found. In contrast, MSNA showed a marked significant curvilinear relationship with age and systolic pressure; sex had a small but statistically significant effect. The α2-adrenergic receptor variants had a similar frequency when hypertensive and normotensive individuals were compared.

CONCLUSION

Variant alleles of three α2-adrenergic receptor subtypes were not related to resting muscle sympathetic nerve hyperactivity, indicating that their functional differences shown in vitro are not reflected in sympathetic activity in man. Age had a marked effect likely influencing arterial pressure through sympathetic activity.

Adrenergic signaling polymorphisms and their impact on cardiovascular disease

This review examines the impact of recent discoveries defining personal genetics of adrenergic signaling polymorphisms on scientific discovery and medical practice related to cardiovascular diseases. The adrenergic system is the major regulator of minute-by-minute cardiovascular function. Inhibition of adrenergic signaling with pharmacological beta-adrenergic receptor antagonists (beta-blockers) is first-line therapy for heart failure and hypertension. Advances in pharmacology, molecular biology, and genetics of adrenergic signaling pathways have brought us to the point where personal genetic differences in adrenergic signaling factors are being assessed as determinants of risk or progression of cardiovascular disease. For a few polymorphisms, functional data generated in cell-based systems, genetic mouse models, and pharmacological provocation of human subjects are concordant with population studies that suggest altered risk of cardiovascular disease or therapeutic response to beta-blockers. For the majority of adrenergic pathway polymorphisms however, published data conflict, and the clinical relevance of individual genotyping remains uncertain. Here, the current state of laboratory and clinical evidence that adrenergic pathway polymorphisms can affect cardiovascular pathophysiology is comprehensively reviewed and compared, with a goal of placing these data in the broad context of potential clinical applicability.

Hypertension in transgenic mice with brain-selective overexpression of the alpha(2B)-adrenoceptor

BACKGROUND

Previous studies have shown that the presynaptic alpha(2B)-adrenoceptor subtype in the central nervous system has a sympathoexcitatory function and its activation leads to a hyperadrenergic hypertensive state. The purpose of this project was to develop a novel hyperadrenergic model, a transgenic (TG) mouse model with brain-selective overexpression of the alpha(2B)-adrenergic receptor (alpha(2B)-AR).

METHODS

We used Southern blot analysis to confirm transgene, real-time PCR to assess gene expression, western Blot analysis and immunohistology to assess protein expression and localization in brain areas. Indirect blood pressure (BP) and heart rate were recorded.

RESULTS

In TG mice there was a 1.8-fold increase in alpha(2B)-AR protein expression compared to wild-type (WT) mice. Immunostaining of brain sections revealed that concentration of alpha(2B)-AR was much more pronounced in TG than in WT mice. Systolic BP at 8 weeks of age was significantly elevated in TG 130 +/- 6 mm Hg, compared with WT control nontransgenic littermates of the same age 107 +/- 7 mm Hg, (P < 0.05), indicating that the TG mice had indeed developed hypertension.

CONCLUSIONS

We have therefore documented that overexpression of the alpha(2B)-AR gene leads to increased production of alpha(2B)-AR protein in brain regions known to regulate central sympathetic outflow, thus resulting in sustained BP elevation. This is a unique model of experimental hypertension driven purely by overexpression of the alpha(2B)-AR that would result in an overactive sympathetic system and would be suitable for testing the pharmacologic properties of potential therapeutic agents.

Presynaptic metabotropic receptors for acetylcholine and adrenaline/noradrenaline

Presynaptic metabotropic receptors for acetylcholine and adrenaline/noradrenaline were first described more than three decades ago. Molecular cloning has resulted in the identification of five G protein-coupled muscarinic receptors (M(1) - M(5)) which mediate the biological effects of acetylcholine. Nine adrenoceptors (alpha(1ABD),alpha(2ABC),beta(123)) transmit adrenaline/noradrenaline signals between cells. The lack of sufficiently subtype-selective ligands has prevented identification of the physiological role and therapeutic potential of these receptor subtypes for a long time. Recently, mouse lines with targeted deletions for all muscarinic and adrenoceptor genes have been generated. This review summarizes the results from these gene-targeting studies with particular emphasis on presynaptic auto- and heteroreceptor functions of muscarinic and adrenergic receptors. Specific knowledge about the function of receptor subtypes will enhance our understanding of the physiological role of the cholinergic and adrenergic nervous system and open new avenues for subtype-selective therapeutic strategies.

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.

Central Sympatholysis as a Novel Countermeasure for Cocaine-Induced Sympathetic Activation and Vasoconstriction in Humans

OBJECTIVES

The aim of this study was to determine whether cocaine's sympathomimetic actions can be reversed by a potent centrally acting alpha2 adrenergic receptor (AR) agonist (dexmedetomidine).

BACKGROUND

We recently showed that cocaine stimulates the human cardiovascular system primarily by acting in the brain to increase sympathetic nerve activity (SNA), the neural stimulus to norepinephrine release. Thus, SNA constitutes a putative new drug target to block cocaine's adverse cardiovascular effects at their origin.

METHODS

In 22 healthy cocaine-naïve humans, we measured skin SNA (microneurography) and skin blood flow (laser Doppler velocimetry) as well as heart rate and blood pressure before and after intranasal cocaine (2 mg/kg) alone and in combination with dexmedetomidine or saline.

RESULTS

During intranasal cocaine alone, SNA increased by 2-fold and skin vascular resistance increased from 13.2 +/- 2.3 to 20.1 +/- 2.2 resistance units while mean arterial pressure increased by 14 +/- 3 mm Hg and heart rate by 18 +/- 3 beats/min (p < 0.01). Dexmedetomidine abolished these increases, whereas intravenous saline was without effect. Dexmedetomidine was effective in blocking these sympathomimetic actions of cocaine even in all 7 subjects who were homozygous for the Del322-325 polymorphism in the alpha2C AR, a loss-of-function mutation that is highly enriched in blacks.

CONCLUSIONS

The data advance the novel hypothesis that central sympatholysis with dexmedetomidine constitutes a highly effective countermeasure for cocaine's sympathomimetic actions on the human cardiovascular system, even in individuals carrying the alpha2CDel322-325 polymorphism. (Study to Improve Scientific Understanding of the Cardiovascular Actions of Cocaine; http://clinicaltrials.gov/ct/show/NCT00338546?order=1; NCT00338546).

Alpha 2-adrenergic receptors decrease DNA replication and cell proliferation and induce neurite outgrowth in transfected rat pheochromocytoma cells

Alpha 2-adrenergic receptors (alpha(2)-ARs) have a widespread distribution in the central nervous system (CNS) and affect a number of biochemical and behavioral functions, including stimulation of prefrontal cortex (PFC) and cognitive function. In addition to its role as a classical neurotransmitter, norepinephrine (NE) has been recently shown to exert an important influence on the plasticity in areas of the brain where neurogenesis persists in the adult, notably the subgranular zone (SGZ) within the dentate gyrus of the hippocampus and the olfactory bulb (OB). In regulating adult neurogenesis, the noradrenergic system is functionally integrated with chronic stress and depression. Chronic stress, depression, or depletion of NE in vivo suppress, and antidepressant treatments induce hippocampal neurogenesis by down- or upregulating, respectively, cell proliferation. In the present study we show that alpha(2)-AR subtypes promote the differentiation rather than cell proliferation of PC12 cells. It is conceivable that alpha(2)-ARs might contribute neurotrophic actions in vivo synergistically or in permutation with other neurotrophic factors.

JP-1302: a new tool to shed light on the roles of alpha2C-adrenoceptors in brain

The discovery of JP-1302 as a selective, high affinity antagonist at the alpha2C-adrenoceptor will enable researchers to probe the functional role and address the therapeutic utility of this potentially highly important adrenoceptor subtype.

Delayed transactivation of the receptor for nerve growth factor is required for sustained signaling and differentiation by alpha2-adrenergic receptors in transfected PC12 cells

Alpha2-adrenergic receptors have been reported to induce subtype-specific neuronal differentiation in vitro, but the signaling mechanisms that mediate this effect have not been characterized. In the present study we found that stimulated alpha2-ARs induce delayed transactivation of TrkA in PC12 cells. The transactivation of TrkA was sensitive to the PP1 inhibitor of the Src family kinases and required prior transactivation of the EGF receptor. Moreover, alpha2-adrenergic receptors induced sustained activation of MAPK and Akt. The sustained activation of Akt, but not of MAPK, was subtype-specific and correlated with the neuronal differentiation of PC12 cells, with the order alpha2A<alpha2B<alpha2C. Furthermore, stimulated alpha2-ARs induced an increased over time expression of the cell cycle associated proteins, p21WAF1 and Cyclin D1 and led to cell cycle arrest in a similar subtype-specific manner. Contrary to sustained activation of MAPK, the persistent activation of Akt and of p21WAF1 and Cyclin D1 as well as neurite outgrowth and expression of the neuronal marker peripherin, were all blocked by K252a an inhibitor of TrkA activity. Together these results demonstrate a novel outcome following alpha2-AR-mediated EGFR transactivation, being the consecutive transactivation of TrkA, and that this event may mediate the subtype-specific differentiation of alpha2-AR-expressing PC12 cells.

The A2B adenosine receptor protects against inflammation and excessive vascular adhesion

Adenosine has been described as playing a role in the control of inflammation, but it has not been certain which of its receptors mediate this effect. Here, we generated an A2B adenosine receptor-knockout/reporter gene-knock-in (A2BAR-knockout/reporter gene-knock-in) mouse model and showed receptor gene expression in the vasculature and macrophages, the ablation of which causes low-grade inflammation compared with age-, sex-, and strain-matched control mice. Augmentation of proinflammatory cytokines, such as TNF-alpha, and a consequent downregulation of IkappaB-alpha are the underlying mechanisms for an observed upregulation of adhesion molecules in the vasculature of these A2BAR-null mice. Intriguingly, leukocyte adhesion to the vasculature is significantly increased in the A2BAR-knockout mice. Exposure to an endotoxin results in augmented proinflammatory cytokine levels in A2BAR-null mice compared with control mice. Bone marrow transplantations indicated that bone marrow (and to a lesser extent vascular) A2BARs regulate these processes. Hence, we identify the A2BAR as a new critical regulator of inflammation and vascular adhesion primarily via signals from hematopoietic cells to the vasculature, focusing attention on the receptor as a therapeutic target.

Loss of alpha2B-adrenoceptors increases magnitude of hypertension following nitric oxide synthase inhibition

Vascular alpha(2B)-adrenoceptors (alpha(2B)-AR) may mediate vasoconstriction and contribute to the development of hypertension. Therefore, we hypothesized that blood pressure would not increase as much in mice with mutated alpha(2B)-AR as in wild-type (WT) mice following nitric oxide (NO) synthase (NOS) inhibition with N(omega)-nitro-l-arginine (l-NNA, 250 mg/l in drinking water). Mean arterial pressure (MAP) was recorded in heterozygous (HET) alpha(2B)-AR knockout mice and WT littermates using telemetry devices for 7 control and 14 l-NNA treatment days. MAP in HET mice was increased significantly on treatment days 1 and 4 to 14, whereas MAP did not change in WT mice (days 0 and 14 = 113 +/- 3 and 114 +/- 4 mmHg in WT, 108 +/- 0.3 and 135 +/- 13 mmHg in HET, P < 0.05). MAP was significantly higher in HET than in WT mice days 10 through 14 (P < 0.05). Thus blood pressure increased more rather than less in mice with decreased alpha(2B)-AR expression. We therefore examined constrictor responses to phenylephrine (PE, 10(-9) to 10(-4) M) with and without NOS inhibition to determine basal NO contributions to arterial tone. In small pressurized mesenteric arteries (inner diameter = 177 +/- 5 microm), PE constriction was decreased in untreated HET arteries compared with WT (P < 0.05). l-NNA (100 microM) augmented PE constriction more in HET arteries than in WT arteries, and responses were not different between groups in the presence of l-NNA. Acetylcholine dilated preconstricted arteries from HET mice more than arteries from WT mice. Endothelial NOS expression was increased in HET compared with WT mesenteric arteries by Western analysis. Griess assay showed increased NO(x) concentrations in HET plasma compared with those in WT plasma. These data demonstrate that diminished alpha(2B)-AR expression increases the dependence of arterial pressure and vascular tone on NO production and that vascular alpha(2B)-AR either directly or indirectly regulates vascular endothelial NOS function.

Hypertension, kidney, and transgenics: a fresh perspective

In this review, we outline the application and contribution of transgenic technology to establishing the genetic basis of blood pressure regulation and its dysfunction. Apart from a small number of examples where high blood pressure is the result of single gene mutation, essential hypertension is the sum of interactions between multiple environmental and genetic factors. Candidate genes can be identified by a variety of means including linkage analysis, quantitative trait locus analysis, association studies, and genome-wide scans. To test the validity of candidate genes, it is valuable to model hypertension in laboratory animals. Animal models generated through selective breeding strategies are often complex, and the underlying mechanism of hypertension is not clear. A complementary strategy has been the use of transgenic technology. Here one gene can be selectively, tissue specifically, or developmentally overexpressed, knocked down, or knocked out. Although resulting phenotypes may still be complicated, the underlying genetic perturbation is a starting point for identifying interactions that lead to hypertension. We recognize that the development and maintenance of hypertension may involve many systems including the vascular, cardiac, and central nervous systems. However, given the central role of the kidney in normal and abnormal blood pressure regulation, we intend to limit our review to models with a broadly renal perspective.

alpha(2)-Adrenergic receptors activate MAPK and Akt through a pathway involving arachidonic acid metabolism by cytochrome P450-dependent epoxygenase, matrix metalloproteinase activation and subtype-specific transactivation of EGFR

Previous study carried out on PC12 cells expressing each alpha(2)-adrenergic receptor subtype individually (PC12/alpha(2A), /alpha(2B) or /alpha(2C)) have shown that epinephrine causes activation of PI3K and phosphorylation of Erk 1/2. The signal transduction mechanisms whereby each alpha(2)-AR subtype triggers these actions were investigated in the present study. In all three clones, epinephrine-induced phosphorylation of MAPK or Akt was abolished by prior treatment with ketoconazole, but not with indomethacin or nordihydroguaiaretic acid. On the other hand, treatment of the clones with epinephrine caused a rapid increase of AA release, which was fully abolished by the PLC inhibitor U73122, but was unaffected by the PLA(2) inhibitor quinacrine. The effects of epinephrine on MAPK and Akt were mimicked by cell exposure to exogenous AA. Furthermore, whereas U73122 abolished the effects of epinephrine, quinacrine only prevented the effects of epinephrine, suggesting that AA release through PLC and its metabolites are responsible for MAPK and Akt activation by alpha(2)-ARs. Treatment with 1,10-phenanthroline, CRM197, or tyrphostin AG1478 suppressed MAPK and Akt phosphorylation by epinephrine or AA, in a subtype-specific manner. Furthermore, conditioned culture medium from epinephrine-treated PC12/alpha(2) induced MAPK and Akt phosphorylation in wild-type PC12. Inhibition of NGFR tyrosine phosphorylation had no effect but the src inhibitor PP1 abolished MAPK and Akt phosphorylation in all three clones. Our results provide evidence for a putative pathway by which alpha(2)-ARs activate MAPK and Akt in PC12 cells, involving stimulation of PLC, AA release, AA metabolism by cytochrome P450-dependent epoxygenase, stimulation of matrix metalloproteinases and subtype-specific transactivation of EGFR through src activation and heparin-binding EGF-like growth factor release.

Alpha(2)-adrenergic receptor signalling in hypertension

Cardiovascular regulation by the sympathetic nervous system is mediated by activation of one or more of the nine known subtypes of the adrenergic receptor family; alpha(1A)-, alpha(1B)-, alpha(1D)-, alpha(2A)-, alpha(2B)-, alpha(2C)-, beta(1)-, beta(2)- and beta(3)-ARs (adrenoceptors). The role of the alpha(2)-AR family has long been known to include presynaptic inhibition of neurotransmitter release, diminished sympathetic efferent traffic, vasodilation and vasoconstriction. This complex response is mediated by one of three subtypes which all uniquely affect blood pressure and blood flow. All three subtypes are present in the brain, kidney, heart and vasculature. However, each differentially influences blood pressure and sympathetic transmission. Activation of alpha(2A)-ARs in cardiovascular control centres of the brain lowers blood pressure and decreases plasma noradrenaline (norepinephrine), activation of peripheral alpha(2B)-ARs causes sodium retention and vasoconstriction, whereas activation of peripheral alpha(2C)-ARs causes cold-induced vasoconstriction. In addition, non-selective agonists elicit endothelium-dependent vasodilation and presynaptic inhibition of noradrenaline release. The evidence that each of these receptor subtypes uniquely participates in cardiovascular control is discussed in this review.

Cardiovascular and metabolic phenotypes in relation to the ADRA2B insertion/deletion polymorphism in a Chinese population

OBJECTIVE

The functional ADRA2B I/D polymorphism is associated with various cardiovascular and metabolic phenotypes in Caucasians. The purpose of our study was to investigate whether the ADRA2B I/D polymorphism is associated with such phenotypes in a Chinese population.

METHODS

We enrolled 247 women and 234 men in a family-based Chinese study. Our statistical methods included generalized estimating equations and quantitative transmission disequilibrium test.

RESULTS

The I allele (62.3 versus 50.8%, P = 0.015) and the II genotype (40.9 versus 23.4%, P = 0.017) were more prevalent among hypertensive than normotensive men. While adjusting for covariates and family clusters, male II homozygotes compared with D-allele carriers had higher systolic pressure (130.0 versus 125.0 mmHg, P = 0.016) and a 2.61 times greater (P = 0.008) risk of hypertension. On the other hand, II homozygous men had lower body weight (65.4 versus 69.6 kg, P = 0.008), body mass index (23.4 versus 24.5 kg/m2, P = 0.037), waist-to-hip ratio (0.838 versus 0.857, P = 0.024), serum insulin concentration (9.5 versus 13.2 mU/l, P = 0.026) and insulin resistance (homeostasis model assessment index 2.4 versus 3.2, P = 0.051). None of these associations reached statistical significance in women. In 65 informative male offspring, transmission of the I allele was associated with higher systolic pressure (+ 6.0 mmHg, P = 0.10), diastolic pressure (+ 5.5 mmHg, P = 0.021), and faster pulse rate (+ 5.8 beats/min, P = 0.019).

CONCLUSION

In Chinese men, the I allele of the ADRA2B gene is associated with higher blood pressure, but also with a more favourable metabolic phenotype.

Cloning and functional characterization of the rat alpha2B-adrenergic receptor gene promoter region: Evidence for binding sites for erythropoiesis-related transcription factors GATA1 and NF-E2

In the rat, the alpha2B-adrenergic receptor (alpha2B-AR) is encoded by the rat non-glycosylated (RNG) gene and is primarily expressed in the kidney, brain and liver of adult animals. High levels of alpha2B-AR are also found during fetal life in the placenta, liver and blood, where it is borne by cells of the erythropoietic lineage. As a first step to define the mechanisms responsible for the spatio-temporal pattern of alpha2B-AR expression, a genomic fragment containing 2.8 kb of the 5'-flanking region, the ORF and approximately 20 kb of the 3'-flanking region of the RNG gene was isolated. RNase protection assays performed on RNA from placenta or kidney using a series of riboprobes permitted to locate the transcription start site 372 bases upstream from the start codon. Transient transfection of various cells, including rat proximal tubule in primary culture, with constructs containing luciferase as a reporter gene demonstrated that: (i) the 5'-flanking region exhibited a strong and sense-dependent transcriptional activity and (ii) the 332 bp fragment (-732/-401 relative to the start codon), which lacks a TATA box but contains Sp1 sites, is sufficient to drive expression. Analysis of chromatin susceptibility to DNaseI digestion identified two hypersensitive sites (HS1 and HS2) located 1.7 and 1.0 kb, respectively, upstream from ATG and containing recognition sequences for erythroid transcription factors. EMSA showed specific binding of GATA1 and NF-E2 to these elements. Taken together, the results suggest that the chromatin environment in the vicinity of these boxes plays a critical role for alpha2B-AR expression during fetal life.

Dexmedetomidine in anaesthesia

PURPOSE OF REVIEW

The development of dexmedetomidine, a potent and highly selective alpha2-adrenoceptor agonist, has created new interest in the use of alpha2-adrenoceptor agonists, and has led to its evaluation in various yet non-approved perioperative settings. The current review focuses on the usefulness of dexmedetomidine in anaesthesia practice.

RECENT FINDINGS

Recently acquired knowledge and experience with dexmedetomidine in perioperative use will be presented and discussed in the context of known pharmacological properties.

SUMMARY

Dexmedetomidine offers beneficial pharmacological properties, providing dose-dependent sedation, analgesia, sympatholysis and anxiolysis without relevant respiratory depression. The side-effects are predictable from the pharmacological profile of (2-adrenoceptor agonists. In particular, the unique sedative properties of dexmedetomidine resulted in several interesting applications in anaesthesia practice, promising benefits in the perioperative use of this compound. However, dexmedetomidine was approved for sedation in the intensive care unit in the USA in 1999, and administration in anaesthesia practice remains an 'off-label' use. Further studies are needed to establish the role of dexmedetomidine in the perioperative period.

Two alpha1-adrenergic receptor subtypes regulating the vasopressor response have differential roles in blood pressure regulation

To study the functional role of individual alpha1-adrenergic (AR) subtypes in blood pressure (BP) regulation, we used mice lacking the alpha1B-AR and/or alpha1D-AR with the same genetic background and further studied their hemodynamic and vasoconstrictive responses. Both the alpha1D-AR knockout and alpha1B-/alpha1D-AR double knockout mice, but not the alpha1B-AR knockout mice, had significantly (p < 0.05) lower levels of basal systolic and mean arterial BP than wild-type mice in nonanesthetized condition, and they showed no significant change in heart rate or in cardiac function, as assessed by echocardiogram. All mutants showed a significantly (p < 0.05) reduced catecholamine-induced pressor and vasoconstriction responses. It is noteworthy that the infusion of norepinephrine did not elicit any pressor response at all in alpha1B-/alpha1D-AR double knockout mice. In an attempt to further examine alpha1-AR subtype, which is involved in the genesis or maintenance of hypertension, BP after salt loading was monitored by tail-cuff readings and confirmed at the endpoint by direct intra-arterial recording. After salt loading, alpha1B-AR knockout mice developed a comparable level of hypertension to wild-type mice, whereas mice lacking alpha1D-AR had significantly (p < 0.05) attenuated BP and lower levels of circulating catecholamines. Our data indicated that alpha1B- and alpha1D-AR subtypes participate cooperatively in BP regulation; however, the deletion of the functional alpha1D-AR, not alpha1B-AR, leads to an antihypertensive effect. The study shows differential contributions of alpha1B- and alpha1D-ARs in BP regulation.

Haplotype-based analysis of alpha 2A, 2B, and 2C adrenergic receptor genes captures information on common functional loci at each gene

The alpha 2-adrenergic receptors (alpha2-AR) mediate physiological effects of epinephrine and norepinephrine. Three genes encode alpha2-AR subtypes carrying common functional polymorphisms (ADRA2A Asn251Lys, ADRA2B Ins/Del301-303 and ADRA2C Ins/Del322-325). We genotyped these functional markers plus a panel of single nucleotide polymorphisms evenly spaced over the gene regions to identify gene haplotype block structure. A total of 24 markers were genotyped in 96 Caucasians and 96 African Americans. ADRA2A and ADRA2B each had a single haplotype block at least 11 and 16 kb in size, respectively, in both populations. ADRA2C had one haplotype block of 10 kb in Caucasians only. For the three genes, haplotype diversity and the number of common haplotypes were highest in African Americans, but a similar number of markers (3-6) per block was sufficient to capture maximum diversity in either population. For each of the three genes, the haplotype was capable of capturing the information content of the known functional locus even when that locus was not genotyped. The alpha2-AR haplotype maps and marker panels are useful tools for genetic linkage studies to detect effects of known and unknown alpha2-AR functional loci.

Clinical and pharmacological significance of α2-adrenoceptor polymorphisms in cardiovascular diseases

The alpha2-adrenoceptors (alpha2-ARs) are receptors for endogenous catecholamines (norepinephrine and epinephrine) that mediate a number of physiological and pharmacological responses such as hypotension and sedation. Three distinct subtypes, denoted alpha2A-, alpha2B- and alpha2C-AR, have been characterized and cloned. Employment of mutation screening in the study of human populations from various ethnic backgrounds has shown that alpha2-AR genes are polymorphic. The functional and biochemical consequences of these polymorphisms have been analyzed by expressing the wild-type receptors and their respective genetic variants in heterologous systems such as CHO and COS-7 cells. Changes include alteration in G-protein coupling and in agonist-promoted receptor phosphorylation and desensitization. Case-control and population-based studies have shown clinical association with cardiovascular risk. Further investigation of the genetic variants in specialized cells and transgenic animals will provide the molecular basis of cardiovascular disease and may reveal alpha2-AR variants as potential targets for selective pharmacological interventions.

α2-Adrenoreceptors Profile Modulation. 2. Biphenyline Analogues as Tools for Selective Activation of the α2C-Subtype

A series of derivatives structurally related to biphenyline (3) was designed with the aim to modulate selectivity toward the alpha(2)-AR subtypes. The results obtained demonstrated that the presence of a correctly oriented function with positive electronic effect (+sigma) in portion X of the ligands is an important factor for significant alpha(2C)-subtype selectivity (imidazolines 5, 13, 16, and 19). Homology modeling and docking studies support experimental data and highlight the crucial role for the hydrogen bond between the pyridine nitrogen in position 3 of 5 and the NH-indole ring of Trp6.48, which is favorably oriented in the alpha(2C)-subtype, only.

Pharmacogenomics of adrenoceptors

Adrenoceptors (ARs) consist of nine subtypes (alpha(1A)-, alpha(1B)-, alpha(1D)-, beta(1)-, beta(2)-, beta(3)-, alpha(2A)-, alpha(2B)- and alpha(2C)-AR), which are involved in a wide spectrum of physiological functions and are the site of action for a considerable percentage of currently prescribed therapeutics. With the exception of alpha(1D), all AR subtypes are polymorphic with genetic variations in the coding and non-coding regions. This review discusses the biochemical consequences of these genetic variations and their impact in receptor function, disease pathophysiology, and drug response. Pharmacogenomic principles that have been discovered are also discussed.

Novel targets of ANG II regulation in mouse heart identified by serial analysis of gene expression

Although the central role of ANG II in cardiovascular homeostasis is well appreciated, the molecular circuitry of its many actions is not completely understood. With the use of serial analysis of gene expression to assess global transcriptional changes in the heart of mice after continuous 7-day ANG II administration, we identified patterns of gene expression indicative of cardiac remodeling, including coordinate regulation of genes previously described in a context of processes associated with hypertrophy and fibrosis. In addition, we discovered several novel ANG II targets, including characterized genes of known function, recently annotated genes of unknown function, and the putative genes not yet present in current databases. The serial analysis of gene expression approach to assess the role of ANG II presented in this report provides new venues for inquiries into ANG II-mediated cardiac function.

Present status of genetic mechanisms in hypertension

Studies on Mendelian hypertension have provided great insight into mechanisms causing hypertension. Mineralocorticoid synthesis and degradation, the mineralocorticoid receptor, sodium channel resorptive mechanisms, and regulation of the thiazide-sensitive sodium-chloride cotransporter have been shown to cause hypertension. Aberrant regulation of peripheral vascular resistance and circulatory regulation have not yet been proved but have been strongly implicated in Mendelian hypertension with brachydactyly. Hypertension as a complex genetic trait has proved more difficult because many genes are involved and the genes have much smaller effects. Association studies, linkage analyses, single nucleotide polymorphism analyses, synteny in animal models, and gene expression studies are the current tools and steady progress is being made.