New class of selective stimulants of beta-adrenergic receptors

L-arginine supplementation reduces mortality and improves disease outcome in mice infected with Trypanosoma cruzi

Chagas disease caused by Trypanosoma cruzi is a neglected disease that affects about 7 million people in Latin America, recently emerging on other continents due to migration. As infection in mice is characterized by depletion of plasma L-arginine, the effect on infection outcome was tested in mice with or without L-arginine supplementation and treatment with 1400W, a specific inhibitor of inducible nitric oxide synthase (iNOS). We found that levels of L-arginine and citrulline were reduced in the heart and plasma of infected mice, whereas levels of asymmetric dimethylarginine, an endogenous iNOS inhibitor, were higher. Moreover, L-arginine supplementation decreased parasitemia and heart parasite burden, improving clinical score and survival. Nitric oxide production in heart tissue and plasma was increased by L-arginine supplementation, while pharmacological inhibition of iNOS yielded an increase in parasitemia and worse clinical score. Interestingly, electrocardiograms improved in mice supplemented with L-arginine, suggesting that it modulates infection and heart function and is thus a potential biomarker of pathology. More importantly, L-arginine may be useful for treating T. cruzi infection, either alone or in combination with other antiparasitic drugs.

Trypanosoma cruzi is the causative agent of the neglected Chagas disease in humans. During infection in mice, depletion of plasma L-arginine is correlated with mortality. L-arginine is a semi-essential amino acid needed for cell proliferation, and is the substrate of arginase 1 (Arg-1) and inducible nitric oxide synthase (iNOS), which is involved in the immune response against infections. Observed L-arginine depletion is likely caused by increased Arg-1 activity, but the effect on immune response are still unknown. Our hypothesis is that L-arginine depletion may block nitric oxide (NO) production by iNOS, which is needed for parasite killing. To test this hypothesis, mice were supplemented with and without L-arginine, and the differential effect of treatment with an iNOS inhibitor was determined. L-arginine supplement was beneficial to the mice, lowering mortality and improving disease outcome and heart function. The beneficial effect was associated with increased levels of NO, thus low levels of L-arginine and NO are considered candidate markers of pathology. Finally, as L-arginine is a common dietary supplement, it may be useful for treatment of Chagas patients, either alone or in combination with antiparasitic drugs.

Salmeterol's extreme β2 selectivity is due to residues in both extracellular loops and transmembrane domains

Salmeterol is a long-acting β2-agonist, widely used as an inhaled treatment of asthma and chronic obstructive pulmonary disease. It has very high β2-affinity (log KD -8.95) and is very selective for the β2-adrenoceptor (1000-fold selectivity over the β1-adrenoceptor). This study used a mutagenesis approach to determine the exact amino acids in the human β2-adrenoceptor responsible for this very high selectivity. Wild-type β2- and β1-adrenoceptors, chimeric β2/β1-adrenoceptors, and receptors with single-point mutations were transfected into Chinese hamster ovary-K1 cells, and affinity and function were studied using [(3)H]CGP 12177 [(-)-4-(3-tert-butylamino-2-hydroxypropoxy)-benzimidazol-2-one] whole-cell binding and [(3)H]cAMP accumulation. Extracellular loop 3 (and specifically amino acid K305) had the largest single effect by reducing salmeterol's affinity for the β2-adrenoceptor by 31-fold. H296 in transmembrane 6 also had a major effect (18-fold reduction in salmeterol affinity). Combining these, in the double mutant β2-H296K-K305D, reduced salmeterol's affinity by 275-fold, to within 4-fold of that of the β1-adrenoceptor, without affecting the affinity or selectivity of other β2-agonists (salbutamol, formoterol, fenoterol, clenbuterol, or adrenaline). Another important amino acid was Y308 in transmembrane 7, although this also affected the affinity and selectivity of other agonists. F194 in extracellular loop 2 and R304 in extracellular loop 3 also had minor effects. None of these mutations (including the double mutant β2-H296K-K305D) affected the efficacy or duration of action of salmeterol. This suggests that the high affinity and selectivity of salmeterol are due to specific amino acids within the receptor itself, but that the duration of action is at least in part due to other factors, for example lipophilicity.

The clinical pharmacology of salmefamol

1 The absorption, excretion and metabolism of [(3)H]-salmefamol, a new sympathomimetic bronchodilator drug, have been studied in asthmatic patients. 2 Following oral administration of 1 or 2 mg to four patients the drug was well absorbed, peak plasma levels occurring from 0.6-2.0 h after administration. An improvement in forced expiratory volume in 1 s (FEV(1)) (ranging from 12-50% above baseline) was seen. 3 Following aerosol administration of 0.22-0.34 mg to four patients a rapid rise in FEV(1) was seen (range 26-117%). The plasma and urinary pictures following this route were similar to those seen after oral administration, suggesting that the majority of the dose was swallowed. 4 Very little free salmefamol was found in plasma or urine, the majority being present as metabolites. Urinary radioactivity was mainly present in the form of sulphate conjugates of at least two compounds, one of which was salmefamol. The other compound has not been identified but it is suggested that it may be an active metabolite.

Effects of time, albuterol, and budesonide on the shape of the flow-volume loop in children with asthma

BACKGROUND

Assessment of asthma through spirometric analysis in children is challenging because of often normal FEV(1) values.

OBJECTIVE

We used Mead's slope ratio (SR; (dV /dV)/(V /V)) to analyze the shape of the flow-volume loop.

METHODS

We analyzed the effects of time, albuterol, and budesonide on FEV(1), FEV(1)/forced vital capacity (FVC) ratio, forced expiratory flow from 25% to 75% of expired volume, and Mead's SR both early (between 75% and 50% of FVC, SR61) and late (between 75% and 50% of FVC, SR35) in exhalation in the Childhood Asthma Management Program cohort at baseline, 4 months, and the end of the study in participants who received either inhaled placebo or budesonide twice daily.

RESULTS

In the placebo group both SR61 and SR35 improved over time. Bronchodilator consistently improved both SR61 and SR35, without change in degree of improvement over time. Similarly, in the budesonide group time and bronchodilator each independently improved both SR61 and SR35. At 4 months and the end of the study, patients receiving budesonide had significant improvements in SR61 relative to patients receiving placebo, which was independent of bronchodilator effect. Budesonide and placebo were not different with respect to prebronchodilator or postbronchodilator SR35.

CONCLUSION

Budesonide-treated patients have less concave flow-volume loops when compared with placebo-treated patients. Time and bronchodilator also make the flow-volume loop less concave. Furthermore, it appears that there are discrete bronchodilator- and corticosteroid-responsive components of airflow obstruction in pediatric asthma.

Using guinea pigs in studies relevant to asthma and COPD

The guinea pig has been the most commonly used small animal species in preclinical studies related to asthma and COPD. The primary advantages of the guinea pig are the similar potencies and efficacies of agonists and antagonists in human and guinea pig airways and the many similarities in physiological processes, especially airway autonomic control and the response to allergen. The primary disadvantages to using guinea pigs are the lack of transgenic methods, limited numbers of guinea pig strains for comparative studies and a prominent axon reflex that is unlikely to be present in human airways. These attributes and various models developed in guinea pigs are discussed.

Very high dose inhaled corticosteroids: panacea or poison?

Perspective on the paper by Paton et al (see page 808)

The childhood asthma epidemic

A case of delayed rather than mistaken diagnosis

The pharmacokinetics of levosalbutamol: what are the clinical implications?

Salbutamol (albuterol) is a beta2-adrenoceptor agonist used as a bronchodilator for the treatment of asthma and as a uterine relaxant for the suspension of premature labour. Salbutamol has been marketed as a racemic mixture, although beta2-agonist activity resides almost exclusively in the (R)-enantiomer. The enantioselective disposition of salbutamol and the possibility that (S)-salbutamol has adverse effects have led to the development of an enantiomerically pure (R)-salbutamol formulation known as levosalbutamol (levalbuterol). Salbutamol is metabolised almost exclusively by sulphotransferase (SULT) 1A3 to an inactive metabolite. (R)-Salbutamol is metabolised up to 12 times faster than (S)-salbutamol. This leads to relatively higher plasma concentrations of (S)- salbutamol following all routes of administration, but particularly following oral administration because of extensive metabolism by the intestine. Enantiomer concentrations are similar for the first hour following an inhaled dose, reflecting the fact that salbutamol in the lung probably undergoes little metabolism. Subsequently, (S)-salbutamol predominates due to absorption and metabolism of the swallowed portion of the inhaled dose. Following oral or inhaled administration of enantiomerically pure salbutamol, a small amount (6%) is converted to the other enantiomer, probably by acid-catalysed racemisation in the stomach. Tissue binding of salbutamol is not enantioselective and plasma protein binding is relatively low. Both enantiomers are actively excreted into the urine. Compared with healthy individuals, patients with asthma do not have substantially different pharmacokinetics of the salbutamol enantiomers, but they do appear to have less drug delivered to the lung following inhaled administration because of their narrowed airways. Levosalbutamol elicits an equal or slightly larger response than an equivalent dose of the racemic mixture. This is probably due to competitive inhibition between the enantiomers at beta-adrenoceptors. Pharmacokinetic-pharmacodynamic relationships for levosalbutamol show relatively large interindividual variations. Functionally significant genetic polymorphisms have been identified for beta2-adrenoceptors, SULT1A3 and organic action transporters, all of which affect the disposition or action of levosalbutamol. Animal, in vitro and some clinical studies have reported deleterious effects of (S)-salbutamol on smooth muscle contractility or lung function. However, well-designed clinical studies in patients with asthma have failed to find evidence of significant toxicity associated with (S)-salbutamol. The clinical consequences of relatively higher plasma concentrations of (S)-salbutamol following administration of racemate remain unclear, but in the absence of clear evidence of toxicity the clinical superiority of levosalbutamol over racemic salbutamol appears to be small.

Enantioselective disposition of albuterol in humans

The study of enantioselective disposition of chiral drugs is important to provide a rationale of plasma concentration-effect relationships, which are often misleading when based on total drug concentration. It is also important when considering new dosage routes or formulations in order to optimize therapeutic plasma concentrations of the active enantiomer. Improvements in the sensitivity and selectivity of biological assays coupled with the developments in chiral analysis have made it possible to study the enantioselective disposition of drugs. Although valuable pharmacokinetic data were obtained for the beta 2-agonists by nonenantioselective methodology, more recent chiral studies have revealed the existence of extensive enantioselectivity in the disposition of these agents. The most significant features of the enantioselective disposition of albuterol are the relatively rapid plasma clearance and low bioavailability of the eutomer. Although this in itself does not necessarily justify the development of a single enantiomer formulation, the implications of the high levels of distomer after i.v. and oral dosing await clarification. Similarly, more work is required to elucidate the consequences of the major difference in disposition between albuterol and terbutaline in humans through both in vivo and in vitro studies of the mechanisms giving rise to this phenomenon. The enantioselective disposition of the other clinically used beta 2-agonists, such as fenoterol, formoterol, and salmeterol also needs to be characterized. The metabolism of the majority of beta 2-agonists is generally by conjugation to give one major metabolite. The situation is therefore uncomplicated by multiple metabolic pathways, which may differ in the extent and direction of their enantioselectivity. Many beta 2-agonists are excreted largely unchanged in the urine making studies of urinary excretion accessible without the requirement for very sensitive assays. The realization that the enantiomers of beta 2-agonists previously thought of as "inactive" may be associated with toxic effects is a further compelling reason to study the enantioselective pharmacokinetics of this class of drugs. In addition, the role of enantiomers in producing side effects, such as tremor and reduction in renal function, needs to be reassessed. The beta 2-agonists can be looked on as textbook examples of the inherent danger of ignoring chirality in the study of pharmacokinetics and pharmacodynamics. The growing body of information on the enantioselective disposition of beta 2-agonists in humans will enhance the rational use of these drugs in the future management of patients.

Studies of the agonist and antagonist activity of cicloprolol in man

To assess the partial agonist activity of cicloprolol in man, four studies were carried out in normal male volunteers. I and II. Open dose escalating studies of the effects of oral doses of the drug on exercise tachycardia and sleeping heart rate. III and IV. Double-blind randomized studies of the effects of placebo, cicloprolol 25 mg, cicloprolol 50 mg, cicloprolol 100 mg, atenolol 50 mg, pindolol 10 mg, salbutamol 8 mg and prenalterol 50 mg on sleeping heart rate, resting supine heart rate, blood pressure, forearm blood flow, finger tremor and exercise tachycardia. All doses of cicloprolol above 2.5 mg reduced an exercise tachycardia but there was no increase in effect above a dose of 50 mg. Cicloprolol caused a dose dependent increase in sleeping heart rate up to 200 mg. Cicloprolol increased resting supine heart rate, systolic blood pressure, forearm blood flow and finger tremor. None of the drugs affected quality of sleep. Cicloprolol has significant partial agonist activity at the beta 1-adrenoceptor as indicated by increases in heart rate and systolic blood pressure. The increases in finger tremor and forearm blood flow suggest that cicloprolol has some partial agonist activity at the beta 2-adrenoceptor.

An assessment of the partial agonist activity of Ro 31-1118, flusoxolol and pindolol in man

1. The effects of single oral doses of three beta-adrenoceptor partial agonists (Ro 31-1118, flusoxolol and pindolol), two beta-adrenoceptor antagonists (propranolol and atenolol), two beta-adrenoceptor agonists (salbutamol and prenalterol) and placebo on sleeping heart rate, quality of sleep, supine heart rate, exercise heart rate, blood pressure, forearm blood flow and finger tremor were studied in eight healthy male volunteers. 2. Sleeping heart rate was increased by Ro 31-1118, flusoxolol, pindolol, salbutamol and prenalterol and decreased by propranolol and atenolol. 3. None of the drugs studied affected quality of sleep. 4. Supine heart rate was increased by flusoxolol, prenalterol and salbutamol, unaffected by Ro 31-1118 and pindolol and reduced by propranolol and atenolol. 5. Exercise heart rate was reduced by both beta-adrenoceptor antagonists and the three partial agonists and unaffected by salbutamol and prenalterol. 6. Systolic blood pressure was increased by Ro 31-1118, flusoxolol, salbutamol and prenalterol, unaffected by pindolol and reduced by propranolol and atenolol. Diastolic blood pressure was reduced by salbutamol and prenalterol. 7. Forearm blood flow was increased by Ro 31-1118, salbutamol and prenalterol, unchanged by pindolol and flusoxolol and decreased by atenolol and propranolol. 8. Finger tremor was increased by Ro 31-1118, flusoxolol, pindolol, salbutamol, and prenalterol. 9. beta-adrenoceptor partial agonists have different effects on the cardiovascular system and finger tremor to beta-adrenoceptor antagonists. 10. While Ro 31-1118 and flusoxolol are antagonists mainly at the beta 1-adrenoceptor they have agonist activity at both beta 1- and beta 2 adrenoceptors. 11. While pindolol is a non-selective antagonist its agonist activity is mainly at the beta 2-adrenoceptor.

Growth of rat salivary glands after terbutaline or dobutamine

Six days after commencement of a regimen of twice daily administration of 25, 50, or 75 mg/kg body wt doses of the beta 1 adrenergic agonist, dobutamine, or the beta 2 adrenergic agonist, terbutaline, submandibular and parotid glands of rats were enlarged in size. The beta 1 receptor was responsible for mediation of these changes with both agonists, since the effects of either agonist were prevented when a 10 mg/kg dose of the beta 1 antagonist, atenolol, was injected 20 min prior to the agonists but were not prevented when the beta 2 antagonist butoxamine, was given prior to each agonist. The increase in gland size caused by dobutamine was more marked than that induced by terbutaline; total amount of DNA of the parotid gland was also higher with dobutamine than with terbutaline. The response of the parotid gland to each dose of either agonist was greater than that of the submandibular gland, suggesting that the parotid gland has more beta receptors than does submandibular gland. The data also show that the increase in cell size precedes an increase in cell number. The increase in cell size depends on activation of fewer receptors than are required for the increase in DNA, since at the same dose of dobutamine, e.g., increase in cell size but not cell number was observed; moreover, the same dosage effected an increase in DNA of parotid but not submandibular gland. The data thus show that enlargement of both glands, as well as increase in size and number of their acinar cells, is dependent on activation of beta 1 adrenoceptors only.

Albuterol: an adrenergic agent for use in the treatment of asthma pharmacology, pharmacokinetics and clinical use

Albuterol is a long-acting beta 2-adrenergic receptor-selective drug that relaxes airway smooth muscle. It is currently available in the United States in oral and metered-dose inhaler forms. Nebulizer solutions and parenteral preparations are likely to be marketed here in the future. The chemical modifications that make albuterol beta 2-selective also promote oral bioavailability and increased duration of action by decreasing sensitivity to degradative enzymes. Albuterol can also produce undesirable dose-related effects: metabolic effects including decreased levels of plasma potassium, phosphate, calcium and magnesium; increased levels of plasma glucose, insulin, renin, lactate and ketones; peripheral vasodilation and perhaps some direct cardiac stimulation resulting in decreased systemic and pulmonary vascular resistance, increased pulse pressure and tachycardia; and skeletal muscle tremor. These side effects are most common with parenteral administration and much less prominent with aerosol administration, which yields lower systemic concentrations. Limited pharmacokinetic data suggest a long distribution phase, a terminal half-life of 3-8 hours, and 10-20% oral bioavailability. Aerosolization of albuterol or a similar agent with a compressed-air nebulizer appears to be best first-line management of the patient with acute dyspneic asthma, but appropriate preparations for this kind of therapy are currently missing from the United States market. Intravenous albuterol has also been employed in acutely dyspneic patients, but produces more side effects than carefully administered intravenous theophylline, is impaired by lack of sufficient pharmacokinetic information to guide dosing, and is of uncertain efficacy in the asthmatic with respiratory failure. However, it appears to lack the potentially life-threatening side effects that can result when theophylline is used carelessly . In the ambulatory patient, aerosolized albuterol (or a similar agent) administered by metered-dose inhaler is an excellent agent for treatment as needed and/or for prevention of acute bronchospasm triggered by exercise or other predictable cause. Advantages include a high degree of efficacy, rapid onset and long duration of effect, and minimal side effects. Regularly scheduled administration of albuterol by metered-dose inhaler is a widely used and effective maintenance medication for patients requiring long-term prophylactic therapy. However comparisons of the ability of this regimen and the other common maintenance regimens (cromolyn and theophylline) to control chronic symptoms of asthma are needed.

Effects of N-aralkyl substitution of beta-agonists on alpha- and beta-adrenoceptor subtypes: pharmacological studies and binding assays

The pharmacological and binding properties of four beta-adrenomimetic drugs with N-alkyl substitutions (isoprenaline, terbutaline, salbutamol and soterenol) were compared with those of four corresponding drugs with N-aralkyl substitutions (protokylol, ME 506, salmefamol and zinterol). BD-40 A, a very powerful beta 2-agonist with a related chemical structure, was also included in this study. The beta 1- and beta 2-activities of these drugs were determined on guinea-pig atria and trachea, their alpha-adrenolytic activity was measured on rat aorta and their affinities (Ki) for alpha 1- and alpha 2-adrenoceptors on rat cortical membranes were assessed using [3H]prazosin and [3H]yohimbine. In this group of beta-agonists, substitution of the N-alkyl by an N-aralkyl group had a variable effect on the beta 2-selectivity whereas alpha-adrenolytic properties were always enhanced. An increase of the affinities (Ki) for both alpha 1- and alpha 2-adrenoceptors was found but the effect was much more pronounced for alpha 1-adrenoceptors. These results indicated that the alpha-adrenolytic activity observed with the N-aralkyl beta-agonists was selective for alpha 1-adrenoceptors.

Contractile and relaxant actions of prostaglandins on guinea-pig isolated trachea

1 The effects of 12 prostaglandins on guinea-pig isolated trachea have been examined in the presence of indomethacin. Two series of experiments were carried out, the first on preparations without tone ('zero tone'), and the second on preparations with tone induced with acetylcholine ('high tone'). 2 The compounds tested fell into two groups. The first, comprising prostaglandins F1 alpha, F2 alpha, F2 alpha acetal, I2 and Wy 17186, contracted both zero and high tone preparations. The second, comprising prostaglandins A1, A2, B1, B2, E1, E2 and F2 beta, contracted zero, but relaxed high tone preparations. Responses to the second group of compounds are probably the resultant of their contractile and relaxant actions. 3 The order of potency for contracting zero tone preparations was prostaglandin E (PGE) greater than F = 1 = Wy 17186 greater than B greater than A, 2-series compounds being 5 to 18 times more potent than 1-series compounds. 4 The order of potency for relaxing high tone preparations was PGE greater than F beta greater than B greater than A greater than Wy 17186 greater than F alpha = I = 0. There was little difference between the potency of 1- and 2-series compounds. 5 The possible relevance of these results to the interpretation of the effects of prostaglandins on human airways is discussed.

Cardiopulmonary effects of fenoterol and salbutamol aerosols

Comparative evaluation of the bronchodilator and cardiovascular effects of cumulative dose of fenoterol and salbutamol (albuterol) aerosols was carried out in an open crossover study on 15 patients with chronic stable reversible airways obstruction. On a weight for weight basis, there was no significant difference in the bronchodilator efficacy of fenoterol and salbutamol; though the heart rates after fenoterol were significantly higher than after salbutamol. Ventricular dysrhythmias requiring premature cessation of the study in four patients were seen with fenoterol; whereas no significant ventricular dysrhythmias were observed with salbutamol. It is concluded that salbutamol has lesser cardiostimulatory effects than fenoterol.

Comparison of the beta-adrenoceptor effects of soterenol and its 3-hydroxy, 4-sulphonamido isomer (MJ6987-1) in isolated tissues from the guninea-pig

1. Soterenol and its 3-hydroxy, 4-methanesulphonamido isomer (MJ6987-1) were compared with isoprenaline for beta-adrenoceptor mediated effects in guinea-pig atrial, tracheal, uterine and ileal preparations. In addition, MJ6987-1 was tested for its effects in the atria of cats, rabbits and rats. 2. Soterenol had a lower intrinsic activity and was approximately two to six times less active than isoprenaline in all preparations. 3. MJ6987-1 was a full agonist, being some 30--200 times less active than isoprenaline at beta 1-receptor sites and greater than 3000 times less active in preparations where beta 2-receptor activation was involved. 4. Change in the position of the ring substituents in soterenol leads to the production of beta 1-receptor selective agonist.

Dependency upon salbutamol inhalers

A case of dependency on salbutamol inhalers has been described. This has been discussed in relation to abuse of other drugs by alveolar absorption and other effects of salbutamol. It is not known whether the dependency is due to the salbutamol itself or to the fluorinated hydrocarbons used as propellants.

Assessment of the selectivity of OPC-2009, a new beta2-adrenoceptor stimulatn, by the use of the blood-perfused trachea in situ and of the isolated blood-perfused papillary muscle of the dog

1 The potency and selectivity of 5-(1-hydroxy-2-isopropylamino)butyl-8-hydroxy carbostyril hydrochloride hemihydrate (OPC-2009), a new beta(2)-adrenoceptor stimulant, was compared with those of isoprenaline, trimetoquinol and salbutamol by the use of blood-perfused tracheal preparations in situ and of blood-perfused papillary muscle preparations of the dog. All drugs were injected intra-arterially.2 All the four drugs decreased tracheal intraluminal pressure (tracheal relaxation) and increased tracheal blood flow in a dose-dependent manner. The four drugs produced a dose-dependent increase in developed tension of papillary muscles. In both preparations the duration of action of isoprenaline and salbutamol was short, whereas that of OPC-2009 and trimetoquinol was long. These effects were antagonized by propranolol.3 Dose-response curves to the four drugs for tracheal relaxation were almost parallel. OPC-2009 was 2.4 times more potent, and trimetoquinol and salbutamol were 2.2 and 6.2 times less potent than isoprenaline in causing tracheal relaxation.4 Dose-response curves to the four drugs for tracheal vasodilatation were also parallel. OPC-2009, trimetoquinol and salbutamol were 3.9, 6.7 and 23 times less potent than isoprenaline.5 Slopes of the dose-response curves to the four drugs for increased developed tension were not parallel; that of OPC-2009 was the least steep, whereas that of isoprenaline was the steepest. Trimetoquinol, salbutamol and OPC-2009 were about 18, 570 and 2400 times less potent than isoprenaline.6 Selectivity calculated from relative potencies indicate that OPC-2009 was about 6000 times, salbutamol about 92 times and trimetoquinol about 8.2 times more selective than isoprenaline for tracheal smooth muscle as compared to ventricular muscle.7 The high potency and selectivity of OPC-2009 for tracheal smooth muscle and its long duration of action suggest its potential usefulness for treatment of bronchial asthma.8 The present results are also compatible with the concept that beta(1)-adrenoceptors in cardiac muscle and beta(2)-adrenoceptors in tracheal and vascular smooth muscle can be distinguished. Furthermore, the results revealed that the beta-adrenoceptors mediating tracheal relaxation and vasodilatation may also be different.

Salmefamol orally in asthmatics - two doses compared

The responses of twelve patients with chronic asthma to salmefamol 1 mg and 2 mg, taken orally, were compared in a double-blind cross-over study. Both produced a rise of 40-50% in PEFR and FEV1. Statistically significant improvements were maintained for three to four hours, and 20% improvements for four to six hours. There was no significantly different effect on ventilatory capacity between the two doses. After the 2 mg dose there was a statistically significant fall in diastolic blood pressure at 1 and 1 1/2 hours. Four patients experienced tremor and this was the only side-effect noted. The possible reasons for failure to demonstrate a greater effect with the higher dose are discussed.

Comparison of salmefamol with salbutamol aerosols in asthamatics

In twelve asthmatic patients 200 mug of salmefamol and salbutamol given by metered aerosol produced a similar initial effect on FEV1, FVC and PEFR without significant effect on heart rate or blood pressure. The duration of effect of salbutamol was approximately 4 hours; there was still an appreciable effect from salmefamol at 8 hours.

Comparison of salmefamol and salbutamol in patients with chronic airways obstruction

1 Inhaled salmefamol, in doses of 100 mug and 200 mug has been compared with inhaled salbutamol, in a dose of 200 mug, and with placebo in patients with airways obstruction. 2 Both salmefamol and salbutamol are potent bronchodilators with a signficantly superior action over placebo at all times up to 8 h after treatment. 3 The mean peak percentage increases in FEV produced by the three active preparations were similar. The decline from peak values was significantly slower with salmefamol than with salbutamol. Neither drug produced tachycardia.

Comparison of respiratory and cardiovascular effects of isoproterenol, propranolol, and practolol in asthmatic and normal subjects

Pulmonary functions, by means of FEV1, FVC, and airway resistance, and cardiovascular responses, i.e., ECG, blood pressure, and pulse contour, were measured in 10 control and 15 symptom-free asthmatic subjects during and after the infusions of isoproterenol, with or without previous administration of propranolol or practolol. Bronchial sensitivity to methacholine and response to isoproterenol after methacholine were also measured. Bronchial sensitivity to methacholine challenge was markedly enhanced by propranolol and the effect of isoproterenol infusion on the pulmonary function was also significantly diminished, whereas practolol did not reveal any effect on bronchial sensitivity to methacholine or isoproterenol. The above changes were much more profound in symptom-free asthmatic subjects than in control subjects. The results suggest that practolol does not significantly affect the beta-2 bronchial receptors, is safe to use in asthmatic subjects, and is consistent with an abnormality of these receptors in bronchial asthma.

A double-blind trial of salmefanol, a new bronchodilator

Salmefamol is a new sympathomimetic drug with predominantly β₂ actions. In a double-blind trial in a group of twenty-four patients with airway obstruction, we have compared the effect of 100 μg of salmefamol given by metered aerosol with that of a placebo aerosol. In the same patients we have also compared the aerosols with subcutaneous adrenaline and subcutaneous atropine, the sequence of treatments being determined by a latin square design.

At all times salmefamol had a significantly greater bronchodilator effect than the placebo. Although the effects of atropine and adrenaline were greater at the earlier times of measurement, that of salmefamol was greater at 4 hr.

New bronchodilator aerosol, salmefamol, in asthma

Twenty-five asthmatics were tested with salmefamol aerosol (200 mug q.d.s.) for a period of 3 months. The ventilatory capacity before and after adrenaline was measured weekly and symptoms were assessed daily using a scoring system over a period of 9 months. The results during the 3 months' treatment with salmefamol were compared with the preceding and succeeding 3-month-periods when patients were receiving either salbutamol aerosol or orciprenaline aerosol. Statistically significant improvements were seen in ventilatory capacity before adrenaline inhalation and in symptom scores while on salmefamol. Ventilatory capacity after adrenaline inhalation remained unchanged throughout the study: thus there was no evidence of tachyphylaxis. A significantly greater number of patients preferred the new drug. Four patients developed slight muscle tremor in the first few days of salmefamol therapy, but there were no changes in haematological or biochemical values after 3 months' therapy. Thus, salmefamol seems to have marked efficacy with low toxicity and is generally well tolerated.

The beta-adrenoceptors of the lung mediating inhibition of antigen-induced histamine release

The beta-adrenoceptor stimulants, isoprenaline (IPR), orciprenaline (OPR), terbutaline (TRB), and ITP were studied for effects on antigen-induced release of histamine from guinea-pig lung tissue and for effects on guinea-pig isolated trachea and heart. The order of potency for the agents in the four funct-ons studied were: (a) inhibition of histamine release, IPR greater than OPR approximately equal to TRB greater than ITP equal 0; (b) heart stimulation, chronotropic effect, IPR greater than OPR greater than ITP approximately equal to TRB; (c) heart stimulation, inotropic effect, IPR greater than OPR greater than ITP greater than TRB; (d) trachea relaxation: IPR greater than TRB greater than OPR greater than ITP. These findings suggest that the beta-adrenoceptors mediating inhibition of antigen-induced release of histamine are more related to those mediating trachea relaxation (beta2) than those mediating cardiac stimulation (beta1).

An economical method of comparing inhaled bronchodilators in reversible diffuse airways obstruction. With special reference to a beta-2 stimulant--salmefamol

Lal, S., Dash, C. H., and Gribben M. D. (1974).Thorax, 29, 317-322. An economical method of comparing inhaled bronchodilators in reversible diffuse airways obstruction: with special reference to a β-2 stimulant—salmefamol. A method is described for comparing the bronchodilator effect of a large number of drugs. It involves self-recording of peak expiratory flow rate by patients at home. From the experience gained, the method was used to compare isoprenaline, orciprenaline, terbutaline, salbutamol, and salmefamol with an inert pressurized aerosol. The results of the comparison show that the method is simple and practical and that salmefamol would seem to have a more prolonged bronchodilator effect than the other drugs tested.

Terbutaline in children with asthma

A double-blind, single-dose trial was carried out on 30 asthmatic children to study the effect of oral terbutaline in two different concentrations and of a placebo on ventilatory function and pulse rate. The higher dose of terbutaline (0·075 mg/kg) gave a satisfactory and prolonged action on ventilation without cardiovascular side effects.