Thymoxamine and airways obstruction

Importance of Alpha-adrenergic Receptor Subtypes in Regulating of Airways Tonus at Patients with Bronchial Asthma

Background:

In this work, effect of Tamsulosin hydrochloride as antagonist of alpha_1A and alpha_1B- adrenergic receptor and effect of Salbutamol as agonist of beta₂- adrenergic receptor in patients with bronchial asthma and increased bronchial reactibility was studied.

Methods:

Parameters of the lung function are determined by Body plethysmography. Raw and ITGV were registered and specific resistance (SRaw) was also calculated. Tamsulosin was administered in per os way as a preparation in the form of the capsules with a brand name of “Prolosin”, producer: Niche Generics Limited, Hitchin, Herts.

Results:

Results gained from this research show that blockage of alpha_1A and alpha_1B- adrenergic receptor with Tamsulosin hydrochloride (0.4 mg and 0.8 mg in per os way) has not changed significantly (p > 0.1) the bronchomotor tonus of tracheobronchial tree in comparison to the inhalation of Salbutamol as agonist of beta₂- adrenergic receptor (2 inh. x 0.2 mg), (p < 0.05). Arterial blood pressure showed no significant decrease following the administration of the dose of 0.8 mg Tamsulosin.

Conclusion:

This suggests that the activity of alpha_1A and alpha_1B- adrenergic receptor in the smooth musculature is not a primary mechanism which causes reaction in patients with increased bronchial reactibility, in comparison to agonists of beta₂ – adrenergic receptor which emphasizes their significant action in the reduction of specific resistance of airways.

Tolerability of carvedilol in patients with heart failure and concomitant chronic obstructive pulmonary disease or asthma

BACKGROUND

A substantial proportion of the population with congestive heart failure (CHF) has concomitant airway disease. Little information exists on the tolerability of carvedilol in patients with chronic obstructive pulmonary disease (COPD). In this study, we assessed the tolerability and efficacy of carvedilol in patients with CHF and concomitant COPD or asthma.

METHODS

Between 1996 and 2000, a total of 487 patients began receiving open-label carvedilol. Forty-three (9%) had COPD (n = 31) or asthma (n = 12). Spirometry supported clinical diagnosis in all, and full pulmonary function testing supported diagnosis in 71%. Sixty percent began carvedilol therapy in the hospital and underwent measurement of peak expiratory flow rates (PEFR) before and after dosing.

RESULTS

In patients with COPD, mean forced expiratory volume in one second (FEV(1)) was 62% +/- 13% predicted, reversibility was 4% +/- 4% with bronchodilators, and FEV(1)/FVC was 62% +/- 8%. Mean PEFR was 325 +/- 115 liter/min before the dose and increased by 17% 2 hours after the carvedilol dose (p = 0.04). In patients with asthma, mean FEV(1) was 80% +/- 17% predicted, reversibility was 13% +/- 7%, and FEV(1)/FVC was 74% +/- 11%. Mean PEFR was 407 +/- 161 liter/min before the dose with no significant change 2 hours after the dose. Carvedilol was introduced safely in 84% of patients with COPD, with only 1 patient withdrawn from therapy for wheezing. In contrast, only 50% of patients with asthma tolerated carvedilol. Survival at 2.5 years was 72%. In survivors, left ventricular end-diastolic diameter decreased from 76 +/- 11 mm to 72 +/- 14 mm (p = 0.01), left ventricular end-systolic diameter decreased from 65 +/- 13 mm to 60 +/- 15 mm (p = 0.01), and fractional shortening increased from 14% +/- 7% to 17% +/- 7% (p = 0.05) at 12 months.

CONCLUSIONS

Patients with CHF and COPD tolerated carvedilol well with no significant reversible airflow limitation, but patients with CHF and asthma tolerated carvedilol poorly. The effect of carvedilol on left ventricular dimensions and function in patients with concomitant airway diseases was similar to that seen in our general group of patients. Asthma remains a contraindication to beta-blockade.

Adrenoceptors in airway smooth muscle

This review examines the roles and functional significance of alpha and beta-adrenoceptor subtypes in airway smooth muscle, with emphasis on human airway function and the influence of asthma. Specifically, we have examined the distribution of beta-adrenoceptors in lung and the influence of age, the epithelium, respiratory viruses and inflammation associated with asthma on airway smooth muscle beta-adrenoceptor function. Sites of action, beta 2-selectivity, efficacy and tolerance are also examined in relation to the use of beta 2-agonists in man. In addition, alpha-adrenoceptor function in airway smooth muscle has been reviewed, with some emphasis on comparing observations made in airway smooth muscle with those in animal models.

Alpha 1-adrenoceptor function and autoradiographic distribution in human asthmatic lung

1. The autoradiographic distribution of alpha 1-adrenoceptors was investigated in non-diseased and asthmatic human lung by use of [3H]-prazosin (H-PZ). To validate binding and autoradiographic methods, H-PZ binding was also measured in rat heart. 2. Significant levels of specific H-PZ binding were detected in sections of rat heart. This binding was associated with a single class of non-interacting sites of high affinity (dissociation constant, Kd = 1.17 +/- 0.26 nM). The maximum binding capacity (Bmax) was 59.5 +/- 4.5 fmol mg-1 protein. 3. In sharp contrast, very low levels of specific H-PZ binding were found in both human nondiseased and asthmatic bronchus, although a high level of binding of [125I]-iodocyanopindolol (I-CYP, 50 pM) to beta-adrenoceptors was detected in these airways. Furthermore, very low levels of autoradiographic grains representing specific H-PZ binding were found in all airway structures in human non-diseased or asthmatic lung parenchyma. 4. Consistent with these data, the alpha-adrenoceptor agonist phenylephrine failed to induce significant increases in tone in bronchi isolated from either non-diseased or asthmatic human lung. Results indicate that asthma does not involve significant increases in airway alpha 1-adrenoceptor function.

Differential effects of alpha-adrenoceptor blockade on essential, physiological and isoprenaline-induced tremor: evidence for a central origin of essential tremor

Intravenous thymoxamine reduced the power of essential tremor but increased that of physiological and isoprenaline-induced tremor. These findings indicate that essential and physiological tremor have dissimilar pathophysiological mechanisms. They also suggest that central adrenergic mechanisms are involved in the pathophysiology of essential tremor and that isoprenaline-induced tremor is not a good model of essential tremor. Furthermore, alpha-adrenoceptor blockers may be a useful therapy for essential tremor.

Prazosin, an alpha 1-adrenoceptor antagonist, partially inhibits exercise-induced asthma

The effect of prazosin, a potent and specific alpha 1-adrenoceptor antagonist given by inhalation (total nebulized 2 mg) was compared with placebo in a double-blind randomized study of 10 atopic asthmatic children. Prazosin significantly (p less than 0.01) reduced the severity of post-exercise bronchoconstriction (maximum fall in peak expiratory flow after exercise 21.4% +/- SEM 6.3% after prazosin compared with 42.5% +/- 7.3% after placebo). This protective action of prazosin suggests that activation of alpha 1-adrenoceptor may be involved in the pathogenesis of exercise-induced asthma either by facilitation of mast-cell mediator release or by direct contraction of bronchial smooth muscle. Prazosin did not significantly change resting bronchomotor tone or histamine-induced bronchoconstriction, suggesting no effect on bronchial smooth muscle contractility.

Inhaled prazosin in asthma

Prazosin, a potent and selective alpha-adrenergic antagonist, was given by inhalation to nine asthmatic subjects aged 25-48 years (six with positive skin tests). Prazosin 0.5 mg, salbutamol 1 mg, or placebo were given by nebuliser in randomised double-blind fashion on separate days. Although all subjects showed a significant increase in FEV1, vital capacity, and maximum expiratory flow at 70% of total lung capacity after salbutamol, there was no significant difference between prazosin and placebo. This suggests that alpha-adrenergic receptors are not important in the control of bronchial tone in asthma. The weak bronchodilatation ascribed to alpha-antagonists in previous studies could be explained by other pharmacological actions of the drugs used.

Indoramin--an alpha adrenoreceptor antagonist for airway obstruction

Indoramin, an alpha adrenoreceptor antagonist, was given in tablet form, in addition to regular salbutamol by aerosol, to 30 patients with airway obstruction. Indoramin produced a small increase in peak flow rate, no change in forced expiratory volume in one second and no improvement in symptoms. Troublesome unwanted effects occurred in six patients.

Investigation of occurrence of tolerance to bronchodilator drugs in chronically pretreated guinea-pigs

1 The actions of sympathomimetic amines on isolated preparations of atria, trachea and ileum were studied in vitro in guinea-pigs, which had been pretreated for 5 or 12 days, by subcutaneous injection, with adrenaline (5 mug/kg), salbutamol (0.5 mug/kg), salbutamol (0.5 mug/kg), methoxamine (250 mug/kg) or saline (0.9% w/V NaCl solution). 2 In the trachea, a decrease in sensitivity (tolerance) to the relaxant effect of adrenaline was induced by pretreatment, for 12 but not for 5 days, with adrenaline. In these animals, cross-tolerance to isoprenaline or salbutamol was not observed. Tolerance to the relaxant actions of adrenaline isoprenaline or salbutamol was not observed after pretreatment with salbutamol. 3 In the trachea, pretreatment with methoxamine or adrenaline for 12 days did not change the sensitivity to the alpha-adrenoceptor-mediated contractor action of methoxamine. 4 In the atria from those guinea-pigs pretreated with adrenaline or salbutamol, there was no reduced sensitivity to the beta-adrenoceptor agonist actions of adrenaline, isoprenaline or salbutamol. In animals pretreated with methoxamine or adrenaline, there was no observable tolerance or cross tolerance to methoxamine with respect to its alpha-adrenoceptor-mediated positive inotropic action in the atria and no unequivocal evidence of a reduced sensitivity to that action of adrenaline. 5 It was confirmed that the twitch-like contractions of the longitudinal muscle of the electrically stimulated ileum were inhibited by sympatomimetic amines acting on alpha- and beta-adrenoceptors. There was no reduced sensitivity to the inhibitory actions of noradrenaline or isoprenaline on the twitch of ileum isolated from animals pretreated with adrenaline, salbutamol or methoxamine for 5 or 12 days. 6 From our results on these three preparations from the same animals, it is concluded that generalizations regarding changes in sensitivity to sympathomimetic amines following their prolonged administration should not be made in any one species.

Evaluation of tolerance after continuous and prolonged oral administration of salbutamol to asthmatic patients

Salbutamol (8 mg) was administered twice daily as a sustained release formulation to twenty-four asthmatic patients for up to four weeks under double-blind conditions. 2. The ability of bronchial smooth muscle to respond was determined by monitoring the response to salbutamol (200 mug) administered by aerosol at set intervals three times a week. 3. There was no evidence of diminishing response during the study period. 4. It is concluded that tolerance to salbutamol does not occur at therapeutic dose levels and that clinical observations of tolerance may be due to other factors.