Acute systemic effects of inhaled salbutamol in asthmatic subjects expressing common homozygous beta2-adrenoceptor haplotypes at positions 16 and 27

AIMS: The relationship between beta2-adrenoceptor polymorphisms at positions 16 and 27, and the acute systemic beta2-adrenoceptor effects of inhaled salbutamol is unclear. We therefore elected to evaluate the influence of common homozygous beta2-adrenoceptor haplotypes on the acute systemic beta2-adrenoceptor effects following inhaled salbutamol in asthmatic subjects. METHODS: An initial database search of 531 asthmatic subjects identified the two commonest homozygous haplotypes at positions 16 and 27 to be Arg16-Gln27 (12%) and Gly16-Glu27 (19%). After a 1-week washout period where all beta2-adrenoceptor agonists were withdrawn, 16 Caucasian subjects (Arg16-Gln27: n = 8 and Gly16-Glu27: n = 8) were given a single dose of inhaled salbutamol (1200 microg), followed by serial blood sampling for serum potassium, along with measurements of diastolic blood pressure and heart rate, at 5-min intervals for 20 min. RESULTS: The two groups were well matched for age, sex, FEV1, and inhaled corticosteroid dose. Baseline values for serum potassium, diastolic blood pressure and heart rate were not significantly different comparing Arg16-Gln27 vs Gly16-Glu27. The mean +/- SEM maximum serum potassium change from baseline over 20 min was significantly greater (P = 0.04) for Arg16-Gln27: -0.37 +/- 0.05 mmol l(-1) vs Gly16-Glu27: -0.23 +/- 0.04 mmol l(-1); 95% CI for difference: -0.01 to -0.28 mmol l(-1). The maximum diastolic blood pressure change from baseline over 20 min was significantly greater (P = 0.0008) for Arg16-Gln27: -13 +/- 1 mmHg vs Gly16-Glu27: -4 +/- 2 mmHg; 95% CI for difference: -5, 14 mmHg. There was no significant difference comparing the maximum heart rate change from baseline for Arg16-Gln27: 10 +/- 3 beats min(-1) vs Gly16-Glu27: 10 +/- 3 beats min(-1). CONCLUSIONS: Caucasian asthmatic subjects with the Arg16-Gln27 haplotype exhibited a greater systemic response to inhaled salbutamol, compared with those with the Gly16-Glu27 haplotype. The attenuated beta2-adrenoceptor response in the Gly16-Glu27 haplotype would be in keeping with increased susceptibility to prior down-regulation by endogenous catecholamines.     

Antagonism of long-acting beta2-adrenoceptor agonism

The established place of regular long-acting beta2-adrenoceptor agonists at step 3 in asthma management guidelines has evolved as a consequence of evidence showing additive effects of salmeterol and formoterol on exacerbation rates, resulting in a putative inhaled corticosteroid sparing effect. There is however, evidence to show that although long-acting beta2-adrenoceptor agonists facilitate using a lower dose of inhaled corticosteroid, this may occur at the expense of suboptimal anti-inflammatory control. This is likely to be the case especially with fixed dose combination inhalers where it is not possible to properly titrate anti-inflammatory therapy with inhaled corticosteroids without also inadvertently overtreating with unnecessarily high doses of long-acting beta2-adrenoceptor agonists. Most patients with mild to moderate persistent asthma can be adequately controlled on monotherapy with inhaled corticosteroid in low or medium dosage, which is considerably cheaper than concomitant use of a long-acting beta2-adrenoceptor agonist. Subsensitivity to long-acting beta2-adrenoceptor agonists is a predictable pharmacological phenomenon which occurs despite concomitant inhaled corticosteroid therapy and occurs more readily for bronchoprotective than bronchodilator effects. Subsensitivity of salbutamol protection against bronchoconstrictor stimuli occurs in patients receiving concomitant long-acting beta2-adrenoceptor agonists, which may be due to beta2-adrenoceptor down-regulation or prolonged receptor occupancy. Prospective large scale long-term studies are required to further define the clinical relevance of beta2-adrenoceptor polymorphisms, to look at clinical control outcomes as well as propensity for subsensitivity. It would therefore make more sense to first of all optimize the dose of anti-inflammatory therapy with inhaled corticosteroid and to then consider adding a long-acting beta2-adrenoceptor agonist for patients who are poorly controlled.     

高血压人群中β_2肾上腺素受体遗传多态性与肥胖相关性研究

目的人类β2肾上腺素受体通过内源性儿茶酚胺从而调控机体脂解作用、糖代谢以及心血管功能。本研究旨在分析β2肾上腺素受体Arg16G ly和G ln27G lu遗传多态性在高血压人群中的分布特征以及他们与肥胖发生的相关性。方法分别采用聚合酶链式反应-限制性片段长度多态性和等位基因特异性聚合酶链式反应的方法对受试者进行基因型分析。应用单因素方差分析和卡方检验进行统计学分析。结果对225名中国汉族原发性高血压患者以及125名健康对照者进行了β2肾上腺素受体Arg16G ly和G ln27G lu基因分型,发现其等位基因的发生频率符合Hardy-W e inberg平衡。在高血压合并肥胖组中,27 G lu等位基因的频率为0.069,明显高于单纯性高血压组和健康对照组(P<0.05),进一步分析发现G ln27G lu多态性与肥胖的这种相关性仅存在于男性高血压患者,而女性受试者缺乏这种联系。单倍型研究发现在男性受试者中,β2肾上腺素受体单倍型与肥胖无相关性。结论结果显示β2肾上腺素受体G ln27G lu遗传多态性可能是导致男性高血压人群对肥胖易感的主要因素之一。     

人类β3肾上腺素受体基因多态性与疾病相关性研究进展

人类β3肾上腺素受体在机体的能量动员和利用的调节中发挥着举足轻重的作用。β3受体基因的第64个密码子发生错义突变,导致色氨酸被精氨酸置换。这个突变在细胞系和分离的人体脂肪组织细胞中均对受体功能产生影响。同时它与2型糖尿病发病提早、胰岛素抵抗的某些特征和肥胖有密切的联系。最近研究发现,Trp64Arg突变与许多其他候选基因的突变有累加和协同作用。本文主要对人类β3肾上腺素受体多态性的功能意义及其与疾病的相关性作一综述。     

A prospective study of the effects of prolonged timolol therapy on α- and β-adrenoceptor and angiotensin II receptor mediated responses in normal subjects

Aims Long-term treatment with β₁-selective adrenergic antagonists gives rise to cross-sensitisation of cardiac β₂-adrenoceptor responses, with no corresponding alteration in β₁-adrenoceptor responses. We performed a prospective randomised double-blind placebo-controlled cross-over study of the effects of nonselective β-blockade with timolol on α-adrenergic and angiotensin II receptor mediated responses in normal subjects. We also wished to study the time course of β₁- and β₂-adrenergic responses after withdrawal of timolol. Methods Six healthy males received timolol 10 mg twice daily or placebo for 14 days. On day 11 of treatment, vascular α₁-, α₂- and angiotensin II receptor responses were assessed by measuring the blood pressure increases in response to intravenous phenylephrine, α-methylnoradrenaline and angiotensin amide respectively, following one dose of timolol 10 mg (to block the β-adrenergic effects of phenylephrine and α-methylnoradrenaline). Both systolic and diastolic blood pressure increased in response to each of these drugs, but these increases were not different on timolol treatment or placebo. Following cessation of treatment with timolol or placebo, β₁- and β₂-adrenoceptor mediated responses were assessed by measuring the heart rate responses to treadmill exercise and intravenous salbutamol infusion respectively. Half each of the subjects underwent this 2 days and 3 days respectively, after the end of treatment. Results Both exercise-induced and salbutamol-induced tachycardia were not different following placebo or 3 days following the end of timolol treatment. However, 2 days following timolol treatment, both were attenuated; the reduction in salbutamol-induced tachycardia was significant, whilst the reduction in exercise tachycardia did not reach statistical significance. We also measured metabolic responses to exercise and to salbutamol infusion. Exercise induced a rise in plasma potassium and noradrenaline. Salbutamol produced a fall in plasma potassium, a rise in plasma glucose and insulin and also a rise in plasma noradrenaline. All of these changes were not different following placebo or 3 days after the end of timolol treatment; by contrast, 2 days following timolol treatment, all were significantly attenuated, with the exception of the rise in plasma glucose. In addition, the rise in both plasma glucose and insulin in response to an oral load of 75 g glucose were not different post-placebo, 2 or 3 days post-timolol. Conclusions These results show that, following 14 days of nonselective β-adrenoceptor blockade with timolol, there is evidence of residual β-adrenoceptor blockade 2 days after drug withdrawal; this finding is in contrast with the known plasma profile of timolol (half-life 3–6 hours), but is consistent with our previous observations of the slow speeds of association and dissociation of timolol with β-adrenoceptors in vitro. There is no evidence, in this study, of β-adrenergic sensitisation following timolol withdrawal, nor of cross-regulation of vascular α₁-, α₂- or angiotensin II receptors in response to nonselective β-adrenoceptor blockade.     

The arginine-16 beta2-adrenoceptor polymorphism predisposes to bronchoprotective subsensitivity in patients treated with formoterol and salmeterol

AIMS: The relationship between beta2-adrenoceptor polymorphisms and bronchoprotective response with long-acting beta2-adrenoceptor agonists is unknown. METHODS: We retrospectively analysed data from six placebo-controlled randomized studies in corticosteroid treated asthmatics where formoterol or salmeterol were administered over a 1-2-week period, with prior 1-2 week washout, assessing the primary end point of methacholine PD20 and adenosine monophosphate PC20, following first and last dose, expressed as doubling dose difference from placebo. RESULTS: There was no significant heterogeneity between the different studies. Patients who had homozygous or heterozygous genotypes containing the arginine-16 polymorphism (Arg16-Arg16 or Arg16-Gly16) had greater bronchoprotective subsensitivity compared with the homozygous glycine-16 genotype (Gly16-Gly16), amounting to a mean doubling dose difference of 1.49 (95% CI 0.50, 2.48), after the last dose. Subsensitivity of response was greater with formoterol than salmeterol after the last dose in all genotypes, especially with the arginine-16 polymorphism, amounting to a doubling dose difference of 3.00 (95% CI 1.01, 4.99) between formoterol and salmeterol. CONCLUSIONS: Our retrospective analysis showed that the arginine-16 polymorphism was associated with subsensitivity of response for bronchoprotection, which was greater for formoterol than salmeterol. A prospective study will be required in order to further evaluate these findings, particularly to assess whether these differences are mirrored by exacerbations.     

Pharmacogenetics of asthma

Recent advances in the extent of knowledge regarding interindividual genetic variation in drug treatment targets and drug metabolizing enzymes has resulted in studies designed to assess the contribution of genetic variability to treatment response in a range of diseases. This review describes the current state of knowledge of genetic variability in key airway targets important in the treatment of asthma. Whilst the genes coding for some key treatment targets contain little polymorphic variation (e.g. the muscarinic M2 and M3 receptors) other genes whose products are important targets in the treatment of asthma contain extensive genetic variation. The best examples of the latter are the beta2-adrenoceptor and the 5-lipoxygenase genes. Genetic variability in both of these genes may account in part for interindividual variability in treatment response. Finally, a number of key targets within the airways remain to be adequately screened for polymorphic variation.     

Human heart beta-adrenoceptors: beta1-adrenoceptor diversification through 'affinity states' and polymorphism

1. In atrium and ventricle from failing and non-failing human hearts, activation of beta(1)- or beta(2)-adrenoceptors causes increases in contractile force, hastening of relaxation, protein kinase A-catalysed phosphorylation of proteins implicated in the hastening of relaxation, phospholamban, troponin I and C-protein, consistent with coupling of both beta(1)- and beta(2)-adrenoceptors to stimulatory G(salpha)-protein but not inhibitory G(ialpha)-protein. 2. Two 'affinity states', namely beta(1H) and beta(1L), of the beta(1)-adrenoceptor exist. In human heart, noradrenaline elicits powerful increases in contractile force and hastening of relaxation. These effects are blocked with high affinity by beta-adenoceptor antagonists, including propranolol, (-)-pindolol, (-)-CGP 12177 and carvedilol. Some beta-blockers, typified by (-)-pindolol and (-)-CGP 12177, not only block the receptor, but also activate it, albeit at much higher concentrations (approximately 2 log units) than those required to antagonize the effects of catecholamines. In human heart, both (-)-CGP 12177 and (-)-pindolol increase contractile force and hasten relaxation. However, the involvement of the beta(1)-adrenoceptor was not immediately obvious because (-)-pindolol- and (-)-CGP 12177-evoked responses were relatively resistant to blockade by (-)-propranolol. Abrogation of cardiostimulant effects of (-)-CGP 12177 in beta(1)-/beta(2)-adrenoceptor double-knockout mice, but not beta(2)-adrenoceptor-knockout mice, revealed an obligatory role of the beta(1)-adrenoceptor. On the basis of these results, two 'affinity states' have been designated, the beta(1H)- and beta(1L)-adrenoceptor, where the beta(1H)-adrenoceptor is activated by noradrenaline and blocked with high affinity by beta-blockers and the beta(1L)-adrenoceptor is activated by drugs such as (-)-CGP 12177 and (-)-pindolol and blocked with low affinity by beta-blockers such as (-)-propranolol. The beta(1H)- and beta(1L)-adrenoceptor states are consistent with high- and low-affinity binding sites for (-)-[(3)H]-CGP 12177 radioligand binding found in cardiac muscle and recombinant beta(1)-adrenoceptors. 3. There are two common polymorphic locations of the beta(1)-adrenoceptor, at amino acids 49 (Ser/Gly) and 389 (Arg/Gly). Their existence has raised several questions, including their role in determining the effectiveness of heart failure treatment with beta-blockers. We have investigated the effect of long-term maximally tolerated carvedilol administration (> 1 year) on left ventricular ejection fraction (LVEF) in patients with non-ischaemic cardiomyopathy (mean left ventricular ejection fraction 23 +/- 7%; n = 135 patients). The administration of carvedilol improved LVEF to 37 +/- 13% (P < 0.005); however, the improvement was variable, with 32% of patients showing pound 5% improvement. Upon segregation of patients into Arg389Gly-beta(1)-adrenoceptors, it was found that carvedilol caused a greater increase in left ventricular ejection faction in patients carrying the Arg389 allele with Arg389Arg > Arg389Gly > Gly389Gly.     

Pharmacokinetics and systemic beta2-adrenoceptor-mediated responses to inhaled salbutamol

AIMS: To examine whether systemic beta2-adrenoceptor responses, such as tachycardia, tremor and hypokalaemia, can be used as a surrogate for the 20 min pharmacokinetic profile of inhaled salbutamol. METHODS: A retrospective analysis of eight separate published studies in healthy volunteers was performed, each with an identical protocol evaluating the early lung absorption profile of a nominal 1200 microg dose of salbutamol given by different inhaler devices. Peak postural finger tremor, plasma potassium and heart rate were assessed. RESULTS: We found the maximum (Cmax) and average (Cav) plasma concentrations of salbutamol to be correlated (P < 0.0001) to change in plasma potassium (Cmax r = 0.904; Cav r = 0.899) and tremor (Cmax r = 0.875; Cav r = 0.857). No significant correlations existed between change in heart rate and Cmax (r = 0.425) or Cav (r = 0.415). CONCLUSIONS: Systemic beta2-adrenoceptor responses, in particular hypokalaemia and tremor, but not heart rate, appear to be good surrogates for evaluating the lung delivery of inhaled salbutamol. Consequently it is suggested that potassium or tremor responses may be used to evaluate the relative lung delivery of salbutamol from different inhaler devices.     

Comparison of the effects of tulobuterol patch and salmeterol in moderate to severe asthma

1. Although the clinical effects of the tulobuterol patch have been reported to include an increase in morning peak expiratory flow (PEF) values and a decrease of symptoms and the frequency of the rescue use of inhaled short-acting beta2-adrenoceptor agonists, no trials comparing the efficacy of the tulobuterol patch to other standard inhaled long-acting beta2-adrenoceptor agonists have yet been conducted. The aim of the present study was to compare the clinical effects of the patch formulation of tulobuterol with those of inhaled salmeterol in moderate to severe asthma. 2. Fifty-four patients with moderate to severe asthma, whose conditions were suboptimally controlled despite receiving inhaled corticosteroids, were recruited. The study was a prospective, randomized trial of cross-over design comparing the effects of 4 weeks treatment with tulobuterol patch, 2 mg once daily, and salmeterol, 50 mg twice daily. The mean prebronchodilator morning PEF during the last 14 days of each treatment period and health-related quality of life (HRQoL) were the primary outcome variables. The HRQoL was assessed using the St George's Respiratory Questionnaire. 3. Forty-four patients (81.5%) completed the trial and were included in the analysis. The mean morning PEF and HRQoL score were significantly improved in both the salmeterol (P < 0.0001 and P < 0.05, respectively) and the tulobuterol patch (P < 0.01 and P < 0.05, respectively) treatment periods compared with the run-in period. Although the mean morning PEF was significantly higher in the salmeterol-treated group than in the tulobuterol-treated group (P < 0.001), the HRQoL scores were comparable. 4. The tulobuterol patch may be useful as a controller medication in addition to inhaled corticosteroids in moderate to severe asthma.     

Contribution of nitric oxide to beta2-adrenoceptor mediated vasodilatation in human forearm arterial vasculature

AIMS: beta2-adrenoceptor agonists are generally considered to produce endothelium independent vasodilatation through adenylate cyclase. We determined whether nitric oxide contributes to beta2-adrenoceptor vasodilatation in human arterial vasculature. METHODS: Forearm blood flow responses to brachial intra-arterial infusions of ritodrine (2.5-50 microg min(-1)), a selective beta2-adrenoceptor agonist, were determined in 24 healthy, normotensive subjects (mean age 22 years, 5F) on two occasions with initial and concomitant administration of L-NMMA (800 microg min(-1)), an NO synthase inhibitor, or noradrenaline (5-30 ng min(-1)), a control constrictor not affecting basal NO activity. Responses to the endothelium dependent vasodilator scrotonin (n = 6) and an endothelium independent vasodilator GTN (n = 9) were also determined. RESULTS: Maximal dilatation to ritodrine during L-NMMA infusion (310+/-32%; mean+/-s.e.mean) was reduced compared to that during noradrenaline infusion (417+/-41%, P<0.05), as were summary responses (1023+/-101 vs 1415+/-130; P<0.05). Responses to GTN were unaffected by L-NMMA compared to noradrenaline; max 177+/-26 vs 169+/-20%, 95% CI for difference -33,48; P=0.68; summary response 361+/-51 vs 396+/-37, 95% CI -142,71; P=0.46. Dilator responses to serotonin were reduced by L-NMMA; max 64+/-20 vs 163+/-26%, P<0.01; summary response 129+/-36 vs 293+/-60; P<0.05) and to a greater extent than ritodrine (58+/-7 vs 25+/-14%, P<0.05). CONCLUSIONS: beta2-adrenoceptor mediated vasodilatation in the human forearm has an NO mediated component. The underlying mechanism for this effect is unclear, but flow mediated vasodilatation is unlikely to be responsible.     

Disposition and bioavailability of the β1-adrenoceptor antagonist talinolol in man

In an open randomized crossover study, the pharmacokinetics and bioavailability of the selective β₁-adrenoceptor antagonist talinolol (Cordanum®—Arzneimittelwerk Dresden GmbH, Germany) were investigated in twelve healthy volunteers (five female, seven male; three poor and nine extensive metabolizers of the debrisoquine hydroxylation phenotype) after intravenous infusion (30 mg) and oral administration (50 mg), respectively. Concentrations of talinolol and its metabolites were measured in serum and urine by HPLC or GC-MS. At the end of infusion a peak serum concentration (C_max) of 631 ± 95 ng mL^?1 (mean ± SD) was observed. The area under the serum concentration-time curve from zero to infinity (AUC_0-∞) was 1433 ± 153 ng h mL^?1. The following parameters were estimated: terminal elimination half life (t_1/2), 10.6 ± 3.3 h; mean residence time, 11.6 ± 3.1 h; volume of distribution, 3.3 ± 0.5 L kg^?1; and total body clearance, 4.9 ± 0.6 mL min^?1 kg^?1. Within 36 h 52.8 ± 10.6% of the administered dose was recovered as unchanged talinolol and 0.33 ± 0.18% as hydroxylated talinolol metabolites in urine. After oral administration a C_max of 168 ± 67 ng mL^?1 was reached after 3.2 ± 0.8h. The AUC_0-∞ was 1321 ± 382 ng h mL^?1. The t_1/2 was 11.9 ± 2.4 h. 28.1 ± 6.8% of the dose or 55.0 ± 11.0% of the bioavailable talinolol was eliminated as unchanged talinolol and 0.26 ± 0.17% of the dose as hydroxylated metabolites by kidney. The absolute bioavailability of talinolol was 55 ± 15% (95% confidence interval, 36–69%). Talinolol does not undergo a relevant first-pass metabolism, and its reduced bioavailability results from incomplete absorption. Talinolol disposition is not found to be altered in poor metabolizers of debrisoquine type.     

A proof of concept study to evaluate putative benefits of montelukast in moderate persistent asthmatics

AIMS: Whether chronic dosing with montelukast confers benefit in patients with moderate to severe asthma remains to be fully established. A proof of concept study was performed evaluating putative benefits with montelukast in moderate persistent asthmatics who were taken off inhaled corticosteroids (ICS) and switched to salmeterol. The latter was done to dissociate the effects of montelukast from ICS. METHODS: Twenty moderate to severe persistent asthmatics completed a randomized double-blind crossover study. Subjects received montelukast 10 mg daily or placebo for 2 weeks each. This was preceded by a 2-week run-in when ICS were discontinued and salmeterol started, and used on a regular basis throughout the study. Measurements were made after run-in and after both randomized treatments. RESULTS: There were no significant sequence effects for responses as to whether placebo or montelukast were given first or second. Methacholine PD20 values after run-in, first and second placebo were 63 micro g, 60 micro g and 64 micro g, respectively (corresponding to 2, 4 and 6 weeks of ICS washout, respectively). Lung function deteriorated pre vs post run-in, which was significant (P < 0.05) for FEF25-75 % predicted. Montelukast conferred significant (P < 0.05) improvements as change from post run-in compared with placebo in methacholine PD20, FEV1 % predicted, FEF25-75 % predicted, diurnal peak expiratory flow, symptoms and salbutamol use. For the primary outcome of methacholine PD20, this amounted to a 1.6-fold difference (95% CI 1.1, 2.5). CONCLUSIONS: In moderate persistent asthmatics switched from taking ICS to salmeterol alone, adding montelukast conferred significant benefits on all parameters of asthma control. Further studies are indicated to evaluate whether montelukast exhibits additive effects to ICS/long-acting beta2-adrenoceptor agonist combination inhalers upon clinically important outcomes.     

Pharmacokinetics of β-adrenoceptor blockers in obese and normal volunteers

Aims Obesity can modify the pharmacokinetics of lipophilic drugs. As β-adrenoceptor blockers (BB) are often prescribed for obese patients suffering from hypertension or coronary heart disease, this study compares the pharmacokinetics of lipophilic β-adrenoceptor blockers in obese and control subjects. Methods Nine obese (157±24% of ideal body weight (IBW) mean±s.d.) and nine non-obese healthy volunteers (98±10% IBW), aged 32±9 years, were included in the study. Subjects were randomly given a single i.v. infusion of one of the following racemic β-adrenoceptor blockers, whose doses (expressed as base per kg of IBW) were: propranolol (0.108 mg), labetalol (0.99 mg) and nebivolol (0.073 mg). The plasma concentrations of unchanged drugs were measured by h.p.l.c. The ionisation constants and lipophilicity parameters of β-adrenoceptor blockers were assessed. Results The pharmacokinetic data for the three drugs were qualitatively similar. There was a trend towards a greater total distribution volume (V_ss ) in obese patients than in controls. However, V_ss expressed per kg body weight was slightly smaller in obese patients. The relationship between V_ss and lipophilicity of five β-adrenoceptor was studied by combining the current results with those previously obtained with a moderately lipophilic drug (bisoprolol) and a hydrophilic one (sotalol). The V_ss of the five drugs was positively and well-correlated (r²=0.90; P<0.01) with their distribution coefficient at pH 7.4 (log D^7.4 ), but not with their partition coefficients. The linear regression coefficients for lean and obese subjects were very similar. Conclusions Lipophilic β-adrenoceptor blockers seem to diffuse less into adipose than into lean tissues. All electrical forms of the drugs (i.e. cations, neutral forms, or zwitterions) present at physiological pH contribute to their tissue distribution, in both obese and lean subjects.Their tissue distribution in obese patients could be restricted by the sum of hydrophobic forces and hydrogen bonds they elicit with macromolecules in lean tissues.     

Synergism between beta 2-adrenoceptor agonists and subtype-selective alpha 1A-adrenoceptor antagonists in the tocolytic effect on pregnant rat uterus in vitro

1. Despite great efforts in recent decades, premature birth is still a leading cause of perinatal morbidity and mortality. beta2-Adrenoceptor agonists are frequently used as tocolytics, although their use is rather controversial. Previous animal studies have revealed that blockade of alpha1A-adrenoceptors results in relaxation of the pregnant rat myometrium. 2. The aim of the present study was to investigate the uterus relaxant effect of the beta2-adrenoceptor agonists (terbutaline, ritodrin) applied together with the subtype-selective alpha1A-adrenoceptor antagonists (WB 4101, 5-methylurapidil) in an in vitro rat model. The main objective of the experiments was to clarify whether there was an additive or a potentiating synergism between the two drug classes. 3. Myometrial rings were taken from female, 22-day pregnant (end-term) Sprague-Dawley rats. Electrical field stimulation (EFS) was used to elicit rhythmical contractions. Non-cumulative concentration-response curves were constructed to the beta2-adrenoceptor agonists and the alpha1A-adrenoceptor antagonists alone and to beta2-adrenoceptor agonists co-administered with the alpha1A-adrenoceptor antagonists. 4. Both groups of drugs inhibited EFS-induced contractions in a dose-dependent way. Administering the beta2-adrenoceptor agonists in combination with the alpha1A-adrenoceptor antagonists resulted in a significant decrease in the EC50 and an increase in the maximal contraction inhibiting effect. 5. The potentiating synergism that has been revealed between beta2-adrenoceptor agonists and alpha1A-adrenoceptor antagonists in the uterus relaxant effect may be of great clinical importance because it could improve the efficacy of therapy of preterm delivery.     

Evaluation of the effect on heart rate variability of a beta2-adrenoceptor agonist and antagonist using non-linear scatterplot and sequence methods

AIMS: To examine the impact on heart rate variability (HRV), of agonism or antagonism at the cardiac beta2-adrenoceptor in healthy volunteers, using standard time-domain summary statistics and non-linear methods (scatterplot and quadrant analysis). METHODS: Under double-blind and randomised conditions (Latin square design), 17 normal volunteers received placebo, salbutamol (beta2-adrenoceptor partial agonist), ICI 118,551 (specific beta2-adrenoceptor antagonist), or salbutamol plus ICI 118,551. Single oral doses of medication (at weekly intervals) were administered at 22.30 h, with HRV assessed from the sleeping heart rates. RESULTS: Salbutamol reduced the long-term (SDNN: 135 ms [120, 156], SDANN: 107 ms [89, 124]) time-domain indicators of HRV compared with placebo (SDNN: 39 [24, 55], SDANN 42 [29, 56], [mean difference [95% confidence intervals of difference]]). Alone, ICI 118,551 did not effect HRV, but in combination blocked the actions of salbutamol. Scatterplot length (944 ms [869, 1019]) and area (222*10(3) ms2 [191, 253]) were reduced by salbutamol compared with placebo; (length difference (164 [98, 230]) and area difference 59 [36, 83]). Scatterplot width (dispersion) was lower at both low (width RR-1 25% salbutamol 277 ms [261, 293]: salbutamol minus placebo 14 ms [0, 28]) and high (width 75% salbutamol 417 [391, 443]: salbutamol minus placebo 41 [20, 62]) heart rates. ICI 118,551 alone did not alter scatterplot parameters but in combination blocked the effect of salbutamol. Cardiac acceleration episodes (i.e. consecutive deltaRR and deltaRRn+1 shorten) were increased following salbutamol 7288 [6089, 8486] compared with placebo -1890 [-2600, -1179]; the beat-to beat difference (deltaRRn+1) was reduced after salbutamol compared with the other treatments. ICI 118,551 did not effect acceleration episodes but reduced the effect of salbutamol when used in combination. CONCLUSIONS: Agonism at the cardiac beta2-adrenoceptor in healthy volunteers with salbutamol altered autonomic balance towards sympathetic dominance; this re-balancing was blocked by ICI 118,551 given in combination with salbutamol. However antagonism at the beta2-adrenoceptor with ICI 118,551 alone did not significantly alter the HRV. The beta2-adrenoceptor modulates HRV in healthy volunteers; the implications of agonism and antagonism at the beta2-adrenoceptor in cardiovascular disease states warrants further investigation.     

Combination of calcium channel blockers and β-adrenoceptor blockers for patients with exercise-induced angina pectoris: a double-blind parallel-group comparison of different classes of calcium channel blockers

AIMS: The combination of calcium channel blockers and beta-adrenoceptor blockers is more effective for the treatment of exercise-induced angina pectoris than beta-adrenoceptor blocker monotherapy. As ischaemia in exercise-induced angina is preceded by increase in heart rate, calcium channel blockers with negative chronotropic properties may perform better for this purpose than nonchronotropic compounds. METHODS: A 335 patient double-blind parallel-group study comparing 14 day treatment with amlodipine 5 and 10 mg, with diltiazem 200 and 300 mg, and mibefradil 50 and 100 mg added to baseline beta-adrenoceptor blocker treatment was performed. Exercise testing (ETT) was performed by bicycle ergometry. RESULTS: Although none of the calcium channel blockers improved duration of exercise or amount of workload, all significantly delayed onset of 1 mm ST-segment depression on ETT (P<0.001 for any treatment vs baseline). In addition, mibefradil, both low and high dose treatment, produced the longest delays (low dose: different from diltiazem and amlodipine by 24.1 and 29.8 s, respectively, P<0. 003 and <0.001; high dose: different from diltiazem and amlodipine by 33.7 and 37.0 s, respectively, P<0.001 and <0.001). These effects were linearly correlated with the reduction in rate pressure product (RPP). Serious symptoms of dizziness occurred significantly more frequently on mibefradil (P<0.05), and 19 patients on mibefradil withdrew from trial. CONCLUSIONS: Calcium channel blockers with negative chronotropic properties provide greater delay of ischaemia in patients with exercise-induced angina, but the concomitant risk of intolerable dizziness attenuates this benefit.     

Intracellular Ca2+ and adrenergic responsiveness of cardiac myocytes in streptozotocin-induced diabetes

1. The contractile function of diabetic hearts is impaired. In addition, the responsiveness of diabetic cardiac muscle to sympathetic stimulation is altered. Previous studies have revealed a depressed response to beta-adrenoceptor stimulation; however, the response to alpha-adrenoceptor activation remains controversial. Because alpha- and beta-adrenoceptor agonists increase cardiac contractility, largely through increased mobilization of intracellular Ca2+, the aim of the present study was to investigate the effects of alpha- and beta-adrenoceptor stimulation on intracellular Ca2+ handling in cardiac myocytes from streptozotocin-induced diabetic rats. 2. Intracellular Ca2+ was measured using fura-2. Under basal conditions (27 degrees C, 2.5 mmol/L extracellular [Ca2+], 0.3 Hz stimulation), there was no significant difference in resting or peak Ca2+ levels between control and diabetic cardiomyocytes. However, the time course of the intracellular Ca2+ transient was significantly prolonged in cells from diabetic hearts. 3. The beta-adrenoceptor agonist orciprenaline (at 10(-7) and 10(-6) mol/L) increased the amplitude of the Ca2+ transient in both groups; however, the extent of potentiation was less in diabetic compared with control cardiomyocytes. Orciprenaline decreased the duration of the transient to the same extent in both groups. 4. The alpha-adrenoceptor agonist phenylephrine (at 10(-7) and 10(-6) mol/L) had no effect on the Ca2+ transient in control myocytes but caused a significant concentration-dependent increase in its amplitude in diabetic cardiomyocytes. Phenylephrine had no effect on the time course of the transient in either group. 5. These results demonstrate differential effects of insulin-dependent diabetes on the responsiveness of cardiomyocytes to alpha- and beta-adrenoceptor stimulation. The heightened response to alpha-adrenoceptor stimulation observed in diabetic cardiomyocytes may partly compensate for the diminished myocardial beta-adrenoceptor response.     

Add-on therapy with montelukast or formoterol in patients with the glycine-16 beta2-receptor genotype

AIMS: We assessed whether montelukast or formoterol provides additive effects to asthmatics not controlled on inhaled corticosteroids, by studying patients who were considered to be genetically susceptible to beta2-receptor down regulation and subsensitivity, and who expressed the homozygous glycine-16 beta2-receptor genotype. METHODS: Fifteen corticosteroid-treated, mild to moderate persistent asthmatics received montelukast 10 mg once daily or formoterol 9 micro g twice daily for 2 weeks, separated by a 2-week placebo run-in and washout, in a double-blind, double-dummy, randomized crossover design. Bronchoprotection against adenosine monophosphate (AMP) challenge (primary endpoint), spirometry and blood eosinophils were measured at trough after placebo, first and last doses. RESULTS: For AMP PC20vs placebo, there were sustained significant (P < 0.05) doubling dilution improvements following first (1.1; 95% CI 0.4, 1.9) and last (1.0; 95% CI 0.3, 1.8) doses of montelukast, and following first (1.3; 95% CI 0.1, 2.6) but not last (0.3; 95% CI -0.9, 1.6) doses of formoterol. Blood eosinophils (x 10(6) l(-1)) were significantly (P < 0.05) suppressed after the last dose of montelukast (-71; 95% CI -3, -140) compared with placebo, while formoterol exhibited a nonsignificant rise (20; 95% CI -92, 132). Neither treatment significantly improved FEV1, FEF25-75 or PEF after 2 weeks. CONCLUSIONS: In genetically susceptible patients with the homozygous glycine-16 genotype, montelukast, but not formoterol, conferred sustained anti-inflammatory properties in addition to inhaled corticosteroid, which were dissociated from changes in lung function after 2 weeks. Thus, assessing lung function may miss potentially beneficial anti-inflammatory effects of montelukast when used as add-on therapy.