The effect of thymoxamine and cromolyn sodium on postexercise bronchoconstriction in asthma

Effect of Inhaled Alpha-Blocker on Airflow Obstruction in Asthma1

A controlled study of the effect on airflow obstruction of 30 mg of the alpha-blocker thymoxamine given by inhalation is reported in 10 patients with chronic stable asthma. No significant change in peak expiratory flow rate was seen with either thymoxamine or placebo in any patient. Alpha-adrenergic receptors are therefore unlikely to contribute significantly to resting bronchomotor tone in chronic stable asthma.

Alpha-adrenoceptor blocking drugs in asthma

The effect of alpha-adrenoceptor blocking drug, thymoxamine alone and in combination with isoprenaline, was studied on the specific airways conductance (SGaw) in ten patients with extrinsic asthma. Thymoxamine when given together with isoprenaline produced significantly greater increase in SGaw as compared to improvement achieved with isoprenaline alone. It is suggested that the potentiation of isoprenaline induced bronchodilatation by thymoxamine is mediated by increased cyclic AMP formation in the bronchial smooth muscle.

Alpha(1L)-, but not alpha(1H)-, adrenoceptor antagonist prevents allergic bronchoconstriction in guinea pigs in vivo

alpha-Adrenoceptors have been classified into alpha(1)- and alpha(2)-adrenoceptors. Recently, the alpha(1)-adrenoceptors were divided into two subtypes: alpha(1L) with low affinity and alpha(1H) with high affinity for prazosin. Little is known concerning the role of each subtype of alpha(1)-adrenoceptor in asthma. We investigated the effects of specific antagonists of alpha(1)- and alpha(2)-, alpha(1H)-, alpha(1L)-, and alpha(2)-adrenoceptors, namely moxisylyte, prazosin, 3-[N-[2-(4-hydroxy-2-isopropyl-5-methylphenoxy) ethyl]-N-methylaminomethyl]-4-methoxy-2, 5, 6-trimethylphenol hemifumarate (JTH-601), and yohimbine, respectively, on antigen-induced airway reactions in guinea pigs. Fifteen minutes after intravenous administration of moxisylyte (0.01, 0.1 or 1 mg/kg), prazosin (0.01, 0.1, 1 or 10 mg/kg), JTH-601 (1, 3, 6 or 10 mg/kg) or yohimbine (0.1 or 1 mg/kg), passively sensitized and artificially ventilated animals received an aerosolized antigen challenge. Bronchial responsiveness to inhaled methacholine was assessed as the dose of methacholine required to produce a 200% increase in the pressure at the airway opening (PC(200)) in non-sensitized animals. JTH-601 and moxisylyte, but not prazosin or yohimbine, dose dependently inhibited antigen-induced bronchoconstriction. None of the tested drugs altered PC(200). JTH-601 significantly reduced leukotriene C(4) levels in bronchoalveolar lavage fluid obtained 5 min after antigen challenge, but prazosin did not. These results indicate that prevention of antigen-induced bronchoconstriction by blockade of alpha-adrenoceptors is due to the inhibition of mediator release via alpha(1L)-adrenoceptor antagonism.

Growth hormone response to exercise in asthmatic and normal children

Maximal growth hormone (GH) increments following exercise were compared in asthmatic (n = 14) and normal (n = 8) children. Exercise, which consisted of 6 min ergometer cycling while breathing cold dry (CD) air, induced asthma in all asthmatic patients but not in normal subjects. Baseline plasma GH levels were similar in both groups. Following exercise, however, asthmatic patients had significantly higher mean GH increments than normal subjects (14.8 vs 4.9 ng/ml, P less than 0.025). To evaluate the possible role of bronchoconstriction in the GH response all subjects exercised again, this time while breathing warm humid (WH) air. Despite the absence of exercise-induced asthma (EIA) while breathing WH air, asthmatic patients still had significantly higher mean GH increments than normal subjects (9.2 vs 2.3 ng/ml, P less than 0.05). We conclude that some asthmatic children show excessive GH secretion after exercise regardless of inspired air conditions or the development of EIA.

Prazosin in the treatment of chronic asthma

The role of prazosin, an alpha 1 adrenoceptor blocker, was investigated in patients with chronic stable asthma who continued to have symptoms despite conventional treatment. Forty patients were entered into a double blind, placebo controlled, crossover trial to examine the effect of adding oral prazosin (2 mg twice daily) to previous medication for three weeks. Sixteen patients withdrew from the study. The remaining 24 patients showed no significant change in peak expiratory flow, FEV1, forced vital capacity (FVC), FEV1/FVC ratio, diary card symptom scores, or dose of beta sympathomimetic.

Bronchial responsiveness to methacholine during airway cooling in normal subjects

In order to investigate the effects of airway cooling on bronchial responsiveness in normal subjects, we measured bronchial responsiveness to inhaled methacholine with and without the inhalation of cold air. Two out of seven subjects showed an increase in baseline respiratory resistance (Rrs) during cooling of the airway but the other five subjects showed little change in their baseline Rrs. All subjects increased bronchial responsiveness to methacholine. Additionally, the threshold dose of methacholine decreased to one-third of the control dose with cooling of the airway. We speculate that airway cooling increased bronchial responsiveness to methacholine in normal subjects presumably due to increased vagal tone, increased alpha-adrenergic activity and/or a release of chemical mediators.

The effect of thymoxamine on guinea-pig ileum contractions

The effects of thymoxamine on the contractions induced in guinea-pig isolated ileum were examined. The drug was tested in a large range of concentrations (10(-8)-10(-4) M). The twitch response induced by acetylcholine was potentiated by low concentrations and inhibited by high concentrations of the alpha 1-blocking drug thymoxamine. The contractions in response to carbachol were always inhibited. Thymoxamine also affected the responses of the ileum to other stimulants: angiotensin, pentagastrin, cholecystokinin. The drug (8 X 10(-5), 5 X 10(-4) M) inhibited the calcium contraction of high K+ depolarized preparations.

Bronchopulmonary effects of phenylephrine and methoxamine in the guinea-pig. Interaction with bronchoconstrictor drugs

The bronchopulmonary effects of phenylephrine (Phe) and methoxamine (Met) were investigated in vitro on isolated guinea-pig tracheas and lung strips and in vivo on pulmonary airway resistance (Raw) in conscious guinea-pigs. Phe, but not Met, relaxed the isolated trachea precontracted with acetylcholine (ACh); this effect was inhibited by propranolol and ascribed to beta-adrenergic stimulation. In the presence of propranolol, both Phe and Met contracted the isolated trachea (-log EC50 were 3.80 +/- 0.37 and 3.04 +/- 0.25 respectively (n = 5] and this effect was competitively antagonized by phentolamine. Phe and Met contracted the isolated lung strips more strongly than the trachea (-log EC50 were 5.14 +/- 0.23 and 4.30 +/- 0.14 respectively (n = 5]. In contrast with the latter, the maximum response was equivalent to that induced by ACh; this effect was also antagonized by phentolamine. In the conscious guinea-pig, Phe (100 and 300 micrograms/kg) and Met (1 and 3 mg/kg) had no effect on Raw but significantly reduced the bronchoconstriction induced by ACh (25 micrograms/kg), histamine (20 micrograms/kg) and serotonin (15 micrograms/kg); this protective effect was unmodified by propranolol (2 mg/kg), yohimbine (1 mg/kg) or piperoxan (0.3 mg/kg) but was significantly inhibited by prazosin (30 micrograms/kg) or AR- C239 (50 micrograms/kg). These results suggest that alpha-adrenergic vasoconstriction with subsequent shrinkage of the bronchial mucosa is responsible for the protective effect of Phe and Met against ACh-induced bronchoconstriction. In isolated lung strips, vasoconstriction would increase tension.

Bucindolol: effects on blood pressure, airways resistance and serum creatine phosphokinase

The effect of bucindolol on pulse, blood pressure and airways resistance was studied in eight patients. One hour after 150 mg bucindolol, a significant decrease in supine, standing and post-exercise blood pressure was observed. No change in blood pressure occurred 10 to 14 h after doses ranging from 50-150 mg indicating that bucindolol has a relatively short duration of action. A dose related inhibition of exercise induced tachycardia was observed consistant with beta-receptor blocking activity. However, there was no change in the resting pulse indicating partial sympathomimetic activity. There was no increase in airways resistance at all doses of bucindolol. Serum creatine phosphokinase increased beyond normal limits in 3 out of 6 patients studied, probably due to a direct effect upon skeletal muscle.

Relation between the antihistaminic effect and the alpha-adrenolytic one of thymoxamine

Thymoxamine, suggested by some authors as a useful drug in the asthma therapy associated with beta-adreno-stimulant agents, tested on smooth tracheal muscle of guinea-pig, showed a stronger antihistaminic activity compared to the alpha-adrenolytic action.

Comparison of the effects of single doses of atenolol and labetalol on airways obstruction in patients with hypertension and asthma

1 The effects of atenolol (100 mg), a cardioselective beta-adrenoceptor blocking agent, and labetalol (300 mg), a combined alpha- and non-selective beta-adrenoceptor blocking agent given in single doses were examined in a double-blind placebo controlled study in 11 asthmatic patients with hypertension. Changes in forced expiratory volume in one second (FEV1) were measured. 2 There were no significant differences between the effects of the active drugs, approximately half the patients having higher FEV1 values during each of the two active treatments. When compared with placebo, labetalol significantly reduced the effect of inhaled salbutamol on FEV1. 3 Whilst beta-adrenoceptor blockings drugs cannot be recommended in patients with airways obstruction, should they inadvertantly be given, labetalol like atenolol may be considered relatively safer then pure non-selective beta-adrenoceptor blocking drugs.

Comparison between an alpha-adrenergic antagonist and a beta 2-adrenergic agonist in bronchial asthma

Fifteen patients suffering from asthma received inhalations of phentolamine, albuterol (salbutamol), a combination of phentolamine and albuterol, and placebo, in a single-blind fashion; the changes in the pulmonary function tests were recorded over a three-hour period. Three patients responded to phentolamine with marked bronchodilatation, whereas severe bronchoconstriction was induced by the drug in two patients. Five patients improved more with phentolamine than with placebo, while all patients improved more markedly with albuterol and still more following inhalation of the combination of both drugs. As a group, there were no statistically significant differences between the responses to phentolamine compared with placebo, or between albuterol alone compared with the combination of both drugs. We concluded that both alpha-antagonist and beta 2-agonist agents act in the same direction in most patients, the beta 2-agonist being the dominant. These results do not offer convincing proof that enhanced alpha-adrenergic activity is the main bronchoconstrictor mechanism even in those few with good response to phentolamine, who also showed very good responsiveness to albuterol. The mechanism of phentolamine-induced bronchoconstriction was discussed, but in the light of presently accepted theories, we were unable to evolve a reasonable explanation.

Protective effect of drugs on bronchoconstriction induced by sulphur dioxide

The response to inhaled sulphur dioxide in eight normal, seven atopic, and 22 asthmatic subjects was studied by measuring thoracic gas volume and airway resistance in a whole-body plethysmograph. The fall in specific airway conductance in relation to the concentration of sulphur dioxide inhaled (0-20 ppm) was determined in all three groups. The specific airway conductance fell significantly in the atopic and asthmatic subjects but not in the normal group. In a double-blind study prior inhalation of disodium cromoglycate caused a significant reduction in the response to sulphur dioxide inhalation in atopic and asthmatic subjects. Prior treatment with inhaled ipratropium bromide blocked the response in the atopic subjects, but the effect was variable in the patients with asthma. Previous treatment with inhaled clemastine also reduced the response in patients with asthma, without causing a change in baseline specific conductance. We conclude that non-allergic bronchial hyperreactivity was increased in the atopic and the asthmatic subjects and that mediator release, in addition to a vagal reflex, has a role in such bronchoconstriction.

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.

Adrenoceptors: molecular nature and role in atopic diseases

Since Szentivanyi proposed the idea that asthma and other atopic diseases are due to a beta adrenergic defect there has been much interest in the role of the adrenergic receptors in allergy. The radioactive ligand binding techniques developed within the last few years have greatly increased our knowledge concerning the molecular nature of the adrenoceptors and the events following receptor stimulation. The adrenoceptors have shown to be very dynamic structures. Their number and affinity may be altered due to various physiological and pharmacological stimuli. Their role in the pathogenesis of atopic diseases has not been definitely settled, but there seem to be a true beta adrenergic hyporesponsiveness and alpha hyperresponsiveness in asthma. This article briefly describes the radioligand binding technique and summarizes our present knowledge of the nature of the alpha and beta adrenoceptors and their possible role in atopic diseases.

Physical Activity and the Asthmatic

In brief: Recent studies suggest that avoiding exercise is unwarranted and detrimental for asthmatics. Although exercise provokes bronchospasm in most asthmatics, the severity of exercise-induced asthma can be reduced by several factors: control of exercise duration; less intense, intermittent exercise; warm-ups; warmer, humid inspired air; aerobic fitness; and drugs. Regular vigorous activity increases fitness, enhances tolerance to attacks, and provides more social and psychological independence. The recent development of protective medications has made such activity possible for many asthmatics. Preexercise cromolyn sodium and beta adrenergic agonists are recommended for blocking or reversing attacks.

Plasma catecholamines during exercise-induced bronchoconstriction in bronchial asthma

Plasma levels of adrenaline and noradrenaline during and after submaximal exercise in patients with bronchial asthma were investigated. Three groups were studied comprising 10 patients with exercise-induced bronchoconstriction (EIB), 10 asthmatic patients without EIB and four normal control subjects. Plasma catecholamines were measured at rest, at the end of exercise, and five and 15 minutes after exercise. Changes in airway resistance were assessed by measuring peak expiratory flow rate. Significant differences in catecholamine levels between reacting and non-reacting patients were found. In 10 patients developing EIB adrenaline and noradrenaline levels had risen significantly by the end of exercise and remained elevated up to the fifth minute of recovery. The rise in catecholamine levels in non-reacting asthmatics was insignificant. In control subjects noradrenaline had increased significantly by the end of exercise.

Alpha-adrenergic hyper-responsiveness in asthma

Because alpha-adrenergic stimulation causes bronchoconstriction, the alpha-adrenergic responsiveness of 21 subjects with allergic asthma was compared with that of 16 subjects with allergic rhinitis and 38 normal control subjects. None of the patients had taken medications for at least 30 days before study. Alpha-adrenergic responsiveness was measured by the capacity of phenylephrine to constrict the cutaneous vascular bed and to dilate the pupillary sphincter muscle. Asthmatic subjects required 4.0 +/- 0.6 ng to reduce their cutaneous blood flow by 50 per cent, whereas normal controls required 32.0 +/- 7.5 ng (P less than 0.005) and subjects with allergic rhinitis required 23.7 +/- 9.4 ng (P less than 0.02). The pupils of asthmatic subjects dilated by greater than 0.5 mm in response to 1.8 +/- 0.14 per cent phenylephrine, patients with allergic rhinitis required 2.4 +/- 0.16 (P less than 0.01), and normal controls needed 2.7 +/- 0.07 (P less than 0.00001). Therefore, the patients with allergic asthma had significantly enhanced alpha-adrenergic responses when compared both to normal subjects and patients with allergic rhinitis; the possibility that increased alpha-adrenergic activity contributes to the asthmatic diathesis warrants further exploration.

Adrenergic responses of asthmatic and normal subjects to submaximal and maximal work levels

The response of the adrenergic system of asthmatic subjects to exercise and the role of plasma catecholamines in exercise-induced asthma were investigated. Plasma levels of norepinephrine and epinephrine were measured at rest, during and after exercise in 7 asthmatic and 9 matched normal subjects. Exercise-induced bronchospasm occurred in all asthmatic subjects following exercise, while no significant change was observed in the normal subjects. The results showed that plasma levels of norepinephrine and epinephrine at rest and changes that occcurred during and after exercise were similar in both normal and asthmatic subjects. These data suggest that the adrenergic response of asthmatics to the same relative exercise stress as reflected in plasma catecholamine levels does not differ from that of normal subjects. It appears that changes in the circulating catecholamines do not play a significant role in the pathogenesis of exercised-induced asthma.