Adrenoceptor Gene Research Articles

2-Adrenoceptor polymorphisms and asthma phenotypes: interactions with passive smoking

The aim of the present study was to assess the effects of possible interactions between beta(2)-adrenoceptor gene polymorphisms and passive smoking on forced expiratory volume in one second (FEV(1)), forced vital capacity (FVC) and exhaled nitric oxide (eNO) in children aged 11 yrs. A cross-sectional analysis of the longitudinal cohort was conducted for associations between beta(2)-adrenoceptor gene polymorphisms and lung function and eNO with regard to passive smoking. Among children exposed to tobacco smoke, those with Arg16 (at least one Arg allele) exhibited lower adjusted mean FEV(1) (2.19 versus 2.38 L) and FVC (2.43 versus 2.64 L) than Gly16 homozygotes. Those with Gln27 (at least one Gln allele) also exhibited a lower adjusted mean FEV(1) relative to Glu27 homozygotes (2.24 versus 2.39 L). Among children with no exposure to smoking, those with Arg16 or Gln27 showed lower adjusted geometric mean eNO levels compared with Gly16 homozygotes (15.4 versus 30.9 ppb) and Glu27 homozygotes (18.0 versus 49.7 ppb). In conclusion, passive smoking had a significant effect on associations between beta(2)-adrenoceptor gene polymorphisms and asthma-related phenotypes, enhancing the relationship between Arg16 and lung function and removing the relationship between Arg16 or Gln27 and exhaled nitric oxide levels.

Association of a beta-2 adrenoceptor (ADRB2) gene variant with a blunted in vivo lipolysis and fat oxidation

Obesity is associated with a blunted beta-adrenoceptor-mediated lipolysis and fat oxidation. We investigated whether polymorphisms in codon 16, 27 and 164 of the beta (2)-adrenoceptor gene (ADRB2) and exon 10 of the G protein beta (3)-subunit gene (GNB3) are associated with alterations in in vivo lipolysis and fat oxidation. Sixty-five male and 43 female overweight and obese subjects (body mass index (BMI) range: 26.1-48.4 kg/m(2)) were included. Energy expenditure (EE), respiratory quotient (RQ), circulating free fatty acid (FFA) and glycerol levels were determined after stepwise infusion of increasing doses of the non-selective beta-agonist isoprenaline (ISO). In women, the Arg16 allele of the ADRB2 gene was associated with a blunted increase in circulating FFA, glycerol and a decreased fat oxidation during ISO stimulation. In men, the Arg16 allele was significantly associated with a blunted increase in FFA but not in glycerol or fat oxidation. These results suggest that genetic variation in the ADRB2 gene is associated with disturbances in in vivo beta-adrenoceptor-mediated lipolysis and fat oxidation during beta-adrenergic stimulation in overweight and obese subjects; these effects are influenced by gene-gender interactions.

β2 Adrenoceptor (ADRB2) Pharmacogenetics and Cardiovascular Phenotypes during Laryngoscopy and Tracheal Intubation

Pharmacogenetics is the study of genetic variations that cause a variable drug response characterized by alteration in drug metabolism or in pharmacodynamics. The polymorphisms in genes encoding receptors relevant to treatment cause variation in sensitivity to many drugs. beta2 Adrenoceptor genetic variation contributes to regulation of blood pressure and hemodynamic changes by mediating peripheral vasodilatation. Laryngoscopy and tracheal intubation associated with hemodynamic changes. Although there are four nonsynomic single-nucleotide polymorphisms (SNPs) of beta2 adrenoceptor gene, codon 16 (Arg16Gly) and codon 27 (Gln27Glu) SNPs are both common and functionally important. In this paper, the authors investigated the beta2 adrenoceptor Gly16 and Glu27 SNPs in response to drugs relevant to anesthesia and how these SNPs impacted upon the cardiovascular phenotypes. The authors measured arterial systolic and diastolic blood pressure, heart rate, and rate-pressure product before induction of anesthesia and 1 min following laryngoscopy and tracheal intubation. Genomic DNA was amplified and genotyped using allele-specific polymerase chain reaction (ASPCR) and restriction fragment length polymorphism (RFLP) assays, respectively. When the authors compared hemodynamic results according to genotypes, the patients with Gln homozygote allele at codon 27 exhibited significant increase of heart rate than patients with Glu allele after laryngoscope and tracheal intubation.

An Insertion/Deletion Polymorphism in the alpha2B Adrenoceptor Gene is Associated with Age at Onset of Type 2 Diabetes Mellitus

Alpha2B adrenoceptor (alpha2B-AR) mediates a variety of functions, including insulin secretion. An insertion/deletion (I/D) polymorphism of the alpha2B-AR gene located on chromosome 2 has recently been described. The aim of the present study was to examine if there is a difference in the D allele frequency of alpha2B-AR gene between type 2 diabetic patients and controls, as well as to ascertain whether the D allele confers an increased risk for earlier onset of diabetes. This study included 199 type 2 diabetic patients and 204 age- and sex-matched healthy volunteers. Genotyping of I/D polymorphism was performed by PCR. No significant difference in the D allele frequency was observed between the two groups (22.1% vs. 19.1%, p = 0.409). Among type 2 diabetic patients, however, presence of the D allele was associated with significantly younger age at onset of diabetes (51.4+/-8.6 vs. 59.2+/-9.7 years, p < 0.001). Multiple stepwise linear regression identified alpha2B I/D genotype as an independent predictor of age at onset of DMT2, explaining 14.3% of its variance. This result indicates that the D allele may be implicated in impaired glucose metabolism leading to earlier manifestation of diabetes in predisposed subjects.

Polymorphisms in the α1A‐adrenoceptor gene do not modify the short‐ and long‐term efficacy of α1‐adrenoceptor antagonists in the treatment of benign prostatic hyperplasia

OBJECTIVE To determine whether a common single nucleotide polymorphism (SNP) in the ADRA1A gene encoding the alpha(1A)-adrenoceptor modifies the short- and long-term efficacy of alpha(1)-adrenoceptor antagonists in the treatment of benign prostatic hyperplasia (BPH). PATIENTS AND METHODS For 254 patients with BPH and/or lower urinary tract symptoms who received alpha(1)-adrenergic antagonists for > or = 3 months, the ADRA1A genotype at position 1475 of the coding region was determined. The patients' short-term response to treatment was determined for four outcome measures, i.e. the International Prostate Symptom Score (IPSS), the IPSS quality-of-life score, peak urinary flow rate, and obstruction grade, stratified by genotype. Eventual BPH-related invasive therapy was used as the outcome for assessing the long-term response to treatment. Genetic variants at positions 834, 896, 898 and 1831 were too rare to be considered in the analysis. RESULTS There were no significant differences for the genotype strata in three of the four outcome measures. Patients with the CC genotype responded significantly better in quality-of-life perception than patients with the CT or TT genotype. There were also no significant differences in the risk of BPH-related invasive therapy among the three genotypes. CONCLUSIONS The 1475C-->T SNP in the ADRA1A gene does not modify the short- and long-term efficacy of alpha(1)-adrenoceptor antagonists for treating BPH. There was a small effect on perceived quality of life but this was not reflected in other variables that measured the treatment response more directly.

The N251K functional polymorphism in the α2A-adrenoceptor gene is not associated with depression: a study in suicide completers

alpha(2A)-Adrenoceptor up-regulation and supersensitivity have been described in the postmortem brains of depressed suicide victims and in the platelets of depressed subjects. The C to G transversion at nucleotide 753 (Asn to Lys change at amino acid 251 or N251K) is a low-frequency polymorphism of the alpha(2A)-adrenoceptor gene that results in a gain-of-function phenotype. A previous study has suggested an association between completed suicide and this polymorphism. The single functional polymorphism N251K was tested in a large sample (n=214) of completed suicides, controlling for the antemortem psychiatric diagnosis, and matched controls (n=176). Postmortem brain DNA was extracted and the alpha(2A)-adrenoceptor gene fragment was amplified by polymerase chain reaction, followed by a StyI restriction endonuclease digestion. Amplified products were sequenced to confirm the presence of the alpha(2A)-adrenoceptor gene fragment where the polymorphism is located. The N251K polymorphism was absent in both suicide victim and control groups. No association between the polymorphism and suicide or depression was established. The N251K polymorphism does not represent a genetic factor to explain the alpha(2A)-adrenoceptor hyperactivity in the brains of depressed suicide victims. Association between suicide and this polymorphism was not replicated.

Correlation between vasoconstrictor roles and mRNA expression of α1‐adrenoceptor subtypes in blood vessels of genetically engineered mice

We examined the contribution of each alpha(1)-adrenoceptor (AR) subtype in noradrenaline (NAd)-evoked contraction in the thoracic aortas and mesenteric arteries of mice. Compared with the concentration-response curves (CRCs) for NAd in the thoracic aortas of wild-type (WT) mice, the CRCs of mutant mice showed a significantly lower sensitivity. The pD(2) value in rank order is as follows: WT mice (8.21) > alpha(1B)-adrenoceptor knockout (alpha(1B)-KO) (7.77) > alpha(1D)-AR knockout (alpha(1D)-KO) (6.44) > alpha(1B)- and alpha(1D)-AR double knockout (alpha(1BD)-KO) (5.15). In the mesenteric artery, CRCs for NAd did not differ significantly between either WT (6.52) and alpha(1B)-KO mice (7.12) or alpha(1D)-KO (6.19) and alpha(1BD)-KO (6.29) mice. However, the CRC maximum responses to NAd in alpha(1D)- and alpha(1BD)-KO mice were significantly lower than those in WT and alpha(1B)-KO mice. Except in the thoracic aortas of alpha(1BD)-KO mice, the competitive antagonist prazosin inhibited the contraction response to NAd with high affinity. However, prazosin produced shallow Schild slopes in the vessels of mice lacking the alpha(1D)-AR gene. In the thoracic aorta, pA(2) values in WT mice for KMD-3213 and BMY7378 were 8.25 and 8.46, respectively, and in alpha(1B)-KO mice they were 8.49 and 9.13, respectively. In the mesenteric artery, pA(2) values in WT mice for KMD-3213 and BMY7378 were 8.34 and 7.47, respectively, and in alpha(1B)-KO mice they were 8.11 and 7.82, respectively. These pharmacological findings were in fairly good agreement with findings from comparison of CRCs, with the exception of the mesenteric arteries of WT and alpha(1B)-KO mice, which showed low affinities to BMY7378. We performed a quantitative analysis of the mRNA expression of each alpha(1)-AR subtype in these vessels in order to examine the correlation between mRNA expression level and the predominance of each alpha(1)-AR subtype in mediating vascular contraction. The rank order of each alpha(1)-AR subtype in terms of its vasoconstrictor role was in fairly good agreement with the level of expression of mRNA of each subtype, that is, alpha(1D)-AR > alpha(1B)-AR > alpha(1A)-AR in the thoracic aorta and alpha(1D)-AR > alpha(1A)-AR > alpha(1B)-AR in the mesenteric artery. No dramatic compensatory change of alpha(1)-AR subtype in mutant mice was observed in pharmacological or quantitative mRNA expression analysis.

A Common β2‐Adrenoceptor Gene Haplotype Protects against Obesity in Swedish Women

The beta2-adrenoceptor gene may be of particular importance for human obesity because catecholamines have a central role in energy expenditure both as neurotransmitters and hormones. The gene is highly polymorphic, and individual polymorphisms have previously been examined for their relationship to obesity, but results are conflicting. We performed a haplotype analysis of the beta2-adrenoceptor gene in 1354 women and 421 men, all healthy and at least second generation Scandinavian and with a large interindividual variation in body fat mass. We found three common haplotypes. One of these haplotypes, identified as T, A, C, C at nucleotide positions -47, 46, 79, and 491, was in its homozygote form more common among lean (18%) than obese (13%) women (p = 0.0028), but there was no association with obesity in men (p = 0.47). Women who were homozygous for this haplotype had lower BMI (p = 0.009) and percentage body fat (p = 0.005) in comparison with those having other haplotypes or being heterozygous for TACC. The data suggest an important role of the beta2-adrenoceptor gene in obesity because a common haplotype has recessive protective effects against excess body fat, at least in women.

Association between bronchodilating response to short‐acting β‐agonist and non‐synonymous single‐nucleotide polymorphisms of β2‐adrenoceptor gene

With beta-agonists being the most widely used agents in the treatment of asthma, in vitro studies reported that beta(2)-adrenergic receptor (ADRB2) polymorphisms are associated with agonist-promoted down-regulation. The present population-based study aimed to evaluate the association between bronchodilating response to inhaled short-acting beta-agonist and two non-synonymous single-nucleotide polymorphisms (SNPs) of ADRB2 (ADRB2-16 and ADRB2-27). Two hundred and nine children with reduction in forced expiratory volume in 1 s of more than 20% on methacholine bronchial challenge underwent bronchodilating response testing 5 min after the inhalation of 200 mug of albuterol. Of these 209, 195 gave peripheral blood for genotyping of ADRB2 polymorphisms. The bronchodilating response was significantly higher in subjects with the homozygous Arg16 than in those with the homozygous Gly16. It was further demonstrated that haplotype pairs of the homozygous Arg16Gln27 and of the heterozygous Arg16Gln27/Gly16Glu27 showed the highest bronchodilating responses, and the haplotype pairs of the homozygous Gly16Gln27 the lowest response. As a whole, the bronchodilating response was more positively associated with the combined quantity of Arg16 and Glu27 polymorphisms than with that of Arg16 alone. Non-synonymous SNPs of ADRB2 at codons 16 and 27 is significantly associated with bronchodilating response to inhaled short acting beta-agonists.

Systematic Review and Meta-Analysis of the Association between β2-Adrenoceptor Polymorphisms and Asthma: A HuGE Review

A number of studies have investigated two common polymorphisms in the beta(2)-adrenoceptor gene, Arg/Gly16 and Gln/Glu27, in relation to asthma susceptibility. The authors performed a meta-analysis of each polymorphism, as well as haplotype analysis, for adult and pediatric populations separately, using published data, supplemented by additional data requested from the original authors. Individual analysis detected no effect of Arg/Gly16 in adults but did suggest a recessive protective effect of Gly16 for children, with an odds ratio of 0.71 (95% confidence interval (CI): 0.53, 0.96) compared with the other genotypes. Results for Gln/Glu27 in adults seem to indicate that heterozygotes are at decreased risk of asthma than either homozygote (odds ratio = 0.73, 95% CI: 0.62, 0.87), although the studies are heterogeneous; in children, the Glu/Glu genotype has a decreased risk of asthma (odds ratio = 0.60, 95% CI: 0.35, 0.99) compared with the other genotypes. Despite the proximity of these two polymorphic sites, the linkage disequilibrium coefficient of 0.41 was not high (p < 0.001). Haplotype analysis suggests that there may be an interaction between the two sites, with a lower risk of asthma associated with the Glu27 allele (compared with Gln27), and that this risk is modified by the allele at position 16.

β2-Adrenoceptor Polymorphisms Relate to Insulin Resistance and Sympathetic Overactivity as Early Markers of Metabolic Disease in Nonobese, Normotensive Individuals

The genes responsible for insulin resistance are also candidate genes for insulin resistance-related diseases, such as obesity and hypertension. Functional polymorphisms in the beta2- and beta3-adrenergic receptors have been reported to be associated with diabetes, hypertension, and obesity. To clarify the relevance of the beta-adrenergic receptor polymorphisms to insulin resistance, we studied their association with polymorphisms of beta2 (Arg16Gly, Gln27Glu) and beta3 (Trp64Arg) adrenoceptor genes. We studied 155 young, nonobese Japanese men using the homeostasis model assessment of insulin resistance (HOMA-IR) to divide individuals into insulin-sensitive and insulin-resistant groups. Insulin resistance in the participants was defined as HOMA-IR equal to or greater than the average plus 1 SD of 3.1. There were 69 men who were insulin resistant and 86 men who were insulin sensitive. Body mass index (BMI), blood pressure (BP), plasma glucose, insulin, leptin, norepinephrine (NE) levels, and the polymorphisms of Arg16Gly and Gln27Glu of the beta2- and Trp64Arg of the beta3-adrenoceptor polymorphisms were measured in all participants. The insulin-resistant group had higher frequency of the Gly16 allele of Arg16Gly compared with the insulin-sensitive group, whereas the frequencies of genotypes or alleles of Gln27Glu and Trp64Arg were similar. The insulin-resistant group had a higher mean HOMA-IR, fasting insulin, NE, and total fat mass compared with levels in the insulin-sensitive group, but the BMI and leptin levels were similar. The subjects carrying the Gly16 allele of the beta2-adrenoceptor gene had a higher mean HOMA-IR, fasting insulin, NE, body fat mass, and BP than those without the Gly16 allele. The Gly16 mutation of the beta2-adrenoceptor gene is associated with increased insulin resistance, adiposity, and BP accompanied by higher plasma NE levels early in the metabolic disease in developing obesity. These findings show an important role of beta2-adrenoceptor gene polymorphisms in the association of insulin resistance in hypertension and obesity.

The functional significance of genetic variation within the β1‐adrenoceptor

The beta-1 adrenoceptor is an archetypal G-coupled protein receptor that controls sympathetic responses in the heart, kidney and adipocytes. It has been widely exploited as a drug target with the development of antagonists to treat cardiovascular diseases such as hypertension, angina and heart failure. Signalling through the receptor is modulated by desensitization and beta1- adrenoceptor down-regulation. It is also affected by in vitro substitution of specific amino acid residues within the beta-1 adrenoceptor. Amino acid substitutions also occur naturally due to polymorphic variation within the human beta-1 adrenoceptor gene itself. Since these variants are common (typically being present in > 5% of the population), the pharmacogenetic implications are enormous. A number of these variants have been identified, although two have been the particular focus of recent publications: a serine to glycine substitution at position 49 (49S > G) and an arginine to glycine at position 389 (389R > G). The data on the in vitro behaviour of these two receptor variants is reviewed here, along with the evidence that they may affect both the risk of cardiovascular disease and the therapeutic response to beta-1 adrenoceptor antagonists.

Addition of a signal peptide sequence to the α1D‐adrenoceptor gene increases the density of receptors, as determined by [3H]‐prazosin binding in the membranes

1. Both in mammalian tissues and in transfected cells, only low levels of alpha1D-adrenoceptors are detected in radioligand binding studies. It has been implicated that the comparatively long N-terminal tail of the alpha1D-adrenoceptor is responsible for the inefficient surface expression of the receptor. 2. In the present study, we created gene constructs for six N-terminally truncated variants of the human alpha1D-adrenoceptor. These constructs were used to transfect Neuro2A cells. We show that the density of alpha1D-adrenoceptors, observed by [3H]-prazosin binding, gradually increased with longer truncations of the N-terminus. This seems to indicate that the long N-terminal tail nonspecifically interferes with receptor translocation to the plasma membrane. 3. The addition of a 16 amino acids long signal peptide to the N-terminus of the wild-type alpha1D-adrenoceptor increased the density of receptor binding sites 10-fold in Neuro2A and COS-7 cells. This indicates that, after the addition of a signal peptide, the long N-terminal tail of the alpha1D-adrenoceptor does not interfere with proper translocation of the receptor to the plasma membrane. This, in turn, indicates that the N-terminal tail of the wild-type alpha1D-adrenoceptor, merely by its long length, hinders the first transmembrane helix of the receptor from being a signal anchor. 4. Neither the wild-type alpha1D-adrenoceptor (for which the expression level of [3H]-prazosin binding sites is low) nor the truncated alpha1D-adrenoceptor variant (for which the expression level of [3H]-prazosin binding sites is high) showed any constitutive activity in stimulating inositol phosphate accumulation. This indicates that the low expression level of [3H]-prazosin binding sites, after transfection with the wild-type alpha1D-adrenoceptor, is not caused by constitutive activity of the receptor and subsequent receptor downregulation.

β1-Adrenoceptor gene polymorphism predicts long-term changes in body weight

The genes controlling long-term weight changes are largely unknown. The beta1 (beta1)-adrenoceptor gene contains two nonsynonomous single nucleotide polymorphisms (SNPs), Ser49Gly and Gly389Arg, that both are functional in human cell lines. We investigated the influence of these two SNPs on short- and long-term changes in body mass index (BMI) in a population-based cohort of 761 women who were examined during pregnancy in 1984-1985 and 15 y thereafter. At entry, no genotype effect on BMI was found. After 15 y, the BMI of women carrying the Gly49-genotype (25.3+/-0.3 kg/m(2)) was higher (P<0.005) than that of Ser49-women (24.4+/-0.2 kg/m(2)). Also, the BMI-increase over 15 y was higher (P=0.018) in Gly49-women (3.3+/-0.2 kg/m(2)) than in Ser49-women (2.8+/-0.1 kg/m(2)). The odds ratio for being overweight after 15 y having the Gly49-genotype was 1.6 (confidence interval 1.1-2.3, P=0.01). No effect of SNP 389 alone on BMI was found but there was a genotype-genotype interaction. Those carrying the Gly49-Gly389 combination increased their BMI about 0.7 kg/m(2) more than other combinations (P=0.025). No genotype effect on BMI changes during pregnancy for either SNP was found. Polymorphism of the beta1-adrenoceptor gene influences long-term weight gain and the incidence of adult-onset overweight in women.

An Insertion/Deletion Polymorphism in the alpha(2B)-Adrenoceptor Gene is not a Genetic Risk Factor for Coronary Artery Disease in the Korean Population

Background and Objectives:Cardiovascular disease (CVD) is a complex multigenic disorder, with significant inheritable elements having important roles relating to environmental factors. Recently, the alpha 2 adrenoceptor (α2-AR) gene has been reported to be involved in the development of coronary artery disease (CAD). The aim of this study was to investigate the relationships between an insertion/deletion (I/D) in α2B-AR and CAD in Korean subjects. Subjects and Methods: The α2B-AR I/D polymorphism, which was located in the third intracellular loop of the receptor polypeptide, was examined in 292 patients (M:F=219:73) with CAD and 151 healthy control subjects (M:F=70:81) who visited the Cardiovascular Genome Center in Yonsei Cardiovascular Hospital. Results:In the patient group, 77 men (35.1%) and 26 women (35.6%) had the I/I genotype; 105 men (47.9%) and 39 women (53.4%) a heterozygous genotype and 37 (17.0%) and 8 (11.0%) the D/D genotype. In the controls, 23 men (32.8%) and 29 women (35.8%) had the I/I genotype; 38 (54.3%) and 39 (48.1%) the I/D genotype and 9 (12.9%) and 13 (16.1%) the D/D genotype. There were no differences in the genotype frequencies between the patient and control groups, either in men or women. From a logistical regression analysis, the α2B-AR genotype was not significantly associated with CAD in our study group. Conclusion:The α2B-AR I/D polymorphism is not a risk factor for CAD in the Korean population. (Korean Circulation J 2005;35:215-220)

Beta2 adrenoceptor Arg16Gly polymorphism, airway responsiveness, lung function and asthma in infants and children.

We have previously reported a relationship between increased airway responsiveness (AR) in infancy and reduced childhood lung function. The current study aimed to determine whether the Arg16Gly polymorphism of the beta2 adrenoceptor (beta2AR) gene was important to this relationship. A cohort that initially numbered 253 individuals underwent assessments of AR and lung function aged 1 month, 6 and 11 years; genotyping for polymorphisms of the beta(2)AR was performed. At 1 month of age, the genotype homozygous Arg16 (n=24) was associated with a mean increase in log dose-response slope (AR) of 0.27 [95% confidence interval (CI) 0.07, 0.49] compared with the genotype homozygous Gly16 (n=58), P=0.01. At 11 years of age, the genotype homozygous Arg16 (n=35) was associated with a mean reduction in the percentage of forced expiratory volume in 1 s of 5.3% [95% CI 0.3, 10.2] compared with the genotype homozygous Gly16 (n=65), P=0.03. There was no association between the Arg16Gly polymorphism and atopy or diagnosed asthma. However, nine of 69 individuals with the genotype homozygous Gly16 were admitted to hospital with asthma compared with five out of 111 individuals with the remaining genotypes (P<0.05). The Arg16Gly polymorphism may be important to the association between increased AR in infancy and reduced lung function in childhood and may also be a determinant of asthma severity in children but not asthma per se.

Functional variant in the (alpha)2B adrenoceptor gene, a positional candidate on chromosome 2, associates with hypertension.

In a genome-wide scan in Scandinavians, we found suggestive linkage between early-onset primary hypertension and a region on chromosome 2. The alpha(2B)-adrenoceptor gene, a candidate gene within this region, harbors a functional insertion/deletion (I/D) polymorphism of three glutamate residues. The aim of this study was to investigate if the DD genotype is associated with hypertension in Swedes. We performed an association study between the I/D polymorphism of the alpha(2B)-adrenoceptor and hypertension in the Skaraborg population. The material consists of all known patients with primary hypertension in Skara (n=772 nondiabetic subjects; n=171 normoalbuminuric type 2 diabetic subjects) and 817 population control subjects. We first compared genotype frequencies between patients with early-onset hypertension (aged 50 years or younger at onset) and subjects with normotension (blood pressure <120/80 mm Hg). Thereafter, the polymorphism was tested for association with hypertension at the population level. When comparing patients with early-onset hypertension and normotensive subjects, the DD versus II genotype was associated with early-onset hypertension when diabetic subjects were excluded from the analysis (OR=2.0; 95% CI=1.2 to 3.5) or when they were not excluded (OR=1.8; 95% CI=1.0 to 3.1). At the population level, the DD versus II genotype was weakly associated with nondiabetic hypertension (OR=1.4; 95% CI=1.0 to 1.8). Our data suggest that carriers of the DD versus II genotype of the alpha(2B)-adrenoceptor are at increased risk for hypertension. The genotypic effect is most evident when comparing groups corresponding to the upper and lower tails of the blood pressure distribution in the population; however, in nondiabetic hypertensive subjects it is weakly detectable even at the population level.

Beta-adrenoceptor polymorphisms.

There can be no doubt that beta(1)-, beta(2)- and beta(3)-adrenoceptor genes have genetic polymorphisms. Two single nucleotide polymorphisms have been described for the beta(1)- (Ser49Gly; Gly389Arg), three for the beta(2)- (Arg16Gly; Gln27Glu; Thr164Ile) and one for the beta(3)-adrenoceptor subtype (Trp64Arg) that might be of functional importance. The possibility that changes in expression or properties of the beta-adrenoceptors due to single nucleotide polymorphisms might have phenotypic consequences influencing their cardiovascular or metabolic function or may contribute to the pathophysiology of several disorders like hypertension, congestive heart failure, asthma or obesity is an idea that has attracted much interest during the last 10 years. At present, it appears that these beta-adrenoceptor polymorphisms are very likely not disease-causing genes, but might be risk factors, might modify disease and/or might influence progression of disease. The aim of this review is to provide an overview of the functional consequences of such beta-adrenoceptor polymorphisms in vitro, ex vivo and in vivo.

Relationship between beta-2 adrenoceptor gene haplotypes and adipocyte lipolysis in women.

The beta(2)-adrenergic receptors are important for adipocyte lipolysis regulation by catecholamines in humans. The beta(2)-adrenoceptor gene is highly polymorphic. The role of these genetic variations for adipocyte lipolysis was investigated. Six single-nucleotide polymorphisms (SNPs) in the promotor region and four SNPs in the coding region (leading to amino-acid substitution) of the beta(2)-adrenoceptor gene were determined in 141 overweight or obese, but otherwise healthy women. Lipolysis experiments were performed on isolated subcutaneous adipocytes. Three homozygous haplotypes (6/6, 4/4 and 2/2) were found that differed about 500-fold in noradrenaline sensitivity or beta(2)-adrenoceptor sensitivity (6/6>2/2>4/4, P=0.01). The haplotypes also differed by 100% in maximum noradrenaline-induced lipolysis rates (6/6>2/2>4/4). However, there was no influence on beta(1)-, beta(3)- or alpha(2)A-adrenoceptor sensitivity. Heterozygosity at one or several SNPs in the haplotypes influenced the beta(2)-adrenoceptor sensitivity significantly. Multiple SNPs in the beta(2)-adrenoceptor gene form several haplotypes that markedly influence beta(2)-receptor function- and catecholamine-induced lipolysis in fat cells. These haplotypes may be important genetic factors behind impaired lipolysis in obesity.

All three alpha2-adrenoceptor types serve as autoreceptors in postganglionic sympathetic neurons.

Postganglionic sympathetic neurons and brain noradrenergic neurons use alpha(2A)- and alpha(2C)-adrenoceptors as presynaptic autoreceptors. The present experiments were carried out in order to see whether they possess presynaptic alpha(2B)-autoreceptors as well. Pieces of atria, vasa deferentia, the occipito-parietal cortex and the hippocampus were prepared from either wildtype (WT) mice or mice in which both the alpha(2A)- and the alpha(2C)-adrenoceptor gene had been disrupted (alpha(2AC)KO). The pieces were incubated with (3)H-noradrenaline and then superfused and stimulated electrically. In a first series of experiments, single pulses or brief, autoinhibition-poor pulse trains were used for stimulation. The alpha(2)-adrenoceptor agonist UK 14,304 (brimonidine) reduced the evoked overflow of tritium in all four tissues from WT mice but did not change it in any tissue from alpha(2AC)KO mice. A different pattern was obtained with medetomidine as alpha(2 )agonist. Like UK 14,304, medetomidine reduced the evoked overflow of tritium in all four tissues from WT mice and did not affect overflow in brain slices from alpha(2AC)KO mice; however, in contrast to UK 14,304, medetomidine reduced evoked overflow also in atrial and vas deferens pieces from alpha(2AC)KO mice, although with a lower maximum and potency than in WT preparations. The alpha-adrenoceptor antagonists rauwolscine, phentolamine, prazosin, spiroxatrine and WB 4101 shifted the concentration-response curve of medetomidine in alpha(2AC)KO atria and vasa deferentia to the right. The pK(d) values of the five antagonists against medetomidine in alpha(2AC)KO atria and vasa deferentia correlated with pK(d) values at prototypical alpha(2B) radioligand binding sites but not at alpha(2A) or alpha(2C) binding sites. In a second series of experiments, autoinhibition-rich pulse trains were used for stimulation. Under these conditions, rauwolscine and phentolamine increased the evoked overflow of tritium from alpha(2AC)KO atrial and vas deferens pieces but not from alpha(2AC)KO brain slices. The increase was smaller (by 40% in atria and by 70% in the vas deferens) than previously observed in WT preparations (by 200-400%). In a last series of experiments, mRNA for the alpha(2B)-adrenoceptor was demonstrated by RT-PCR in thoracolumbar sympathetic ganglia from WT, alpha(2A)KO, alpha(2C)KO and alpha(2AC)KO mice but not from alpha(2B)KO mice. The results show that brain noradrenergic neurons express only alpha(2A)- and alpha(2C)-adrenoceptors as autoreceptors. Postganglionic sympathetic neurons, however, can express alpha(2B)-adrenoceptors as presynaptic autoreceptors as well. The alpha(2B)-autoreceptors are activated by medetomidine but not by UK 14,304. They are also activated by previously released noradrenaline. The two-alpha(2)-autoreceptor hypothesis has to be replaced by a three-autoreceptor hypothesis for postganglionic sympathetic neurons.