The low-affinity site of the beta1-adrenoceptor and its relevance to cardiovascular pharmacology.

beta-Adrenoceptor blocking agents (beta-blockers) that at low concentrations antagonize cardiostimulant effects of catecholamines, but at high concentrations also cause cardiostimulation, have been appearing since the late 1960s. These cardiostimulant beta-blockers, coined non-conventional partial agonists, antagonize the effects of catecholamines through a high-affinity site (beta(1H)AR), but cause cardiostimulation mainly through a low-affinity site (beta(1L)AR) of the myocardial beta(1)-adrenoceptor. The experimental non-conventional partial agonist (-)-CGP12177 increases cardiac L-type Ca(2+) current density and Ca(2+) transients, shortens action potential duration but augments action potential plateau, increases heart rate and force, as well as causes arrhythmic Ca(2+) transients and arrhythmic cardiocyte contractions. Other beta-blockers, which do not cause cardiostimulation, consistently have lower affinity for beta(1L)AR than beta(1H)AR. These sites were verified and the cardiac pharmacology of non-conventional partial agonists confirmed on recombinant beta(1)-adrenoceptors and on beta(1)-adrenoceptors overexpressed into the heart. A targeted mutation of Asp138 to Glu138 virtually abolished the pharmacology of beta(1H)AR but left intact the pharmacology of beta(1L)AR. Non-conventional partial agonists may be beneficial for the treatment of peripheral autonomic neuropathy but probably due to their arrhythmic propensities, may be harmful for the treatment of chronic heart failure.

A brief history of inhaled asthma therapy over the last fifty years.

This year is the 50th anniversary of the introduction into clinical use of the first modern inhaler for the management of asthma--the pressurised metered-dose inhaler (pMDI). The pMDI was initially used for the administration of the non-selective beta-agonists adrenaline and isoprenaline. However, the epidemic of asthma deaths which occurred in the 1960s led to these drugs being superseded by the selective short-acting beta-agonist salbutamol, and the first inhaled corticosteroid (ICS) beclomethasone. At the same time, sodium cromoglycate was introduced, to be administered via the first dry-powder inhaler--the Spinhaler--but owing to its relatively weak anti-inflammatory action its use is now very limited. Over the last 10 years, the long-acting beta-agonists (LABAs) have become an important add-on therapy for the management of asthma, and they are now often used with ICS in a single ICS/LABA combination inhaler.

Current issues with beta2-adrenoceptor agonists: historical background.

The discovery that dessicated adrenal glands had beneficial effects in asthma arose in 1900 following a vogue for studying organotherapy at the end of the 19th century. The adrenal hormone adrenaline was found to have sympathomimetic properties and was isolated and synthesized in 1901. The first nonselective beta-agonist, isoproterenol, was isolated in 1940, followed by the development of selective beta2-agonists in the 1960s and the introduction of the long-acting beta2-agonists in the 1990s. The introduction of beta2-selectivity reduced adverse effects, as did developments in inhaler technology that allowed subjects to inhale much smaller doses of drug selectively to the airways. The beta2-agonists are some of the more important drugs to have been developed in the 20th century. Excessive doses can cause problems, and attempts to maximize the benefit from beta2-agonists and to reduce adverse effects has led to considerable epidemiological, clinical, and mechanistic research over the last 50 yr.

Drugs for asthma.

Current drug therapy for asthma is highly effective and has evolved from naturally occurring substances through logical pharmaceutical developments. Pharmacology has played a critical role in asthma drug development and several key experimental observations have been published in this journal. Understanding the pharmacology of effective drug therapies has also taught us much about the underlying mechanisms of asthma. beta(2)-Adrenoceptor agonists are the most effective bronchodilators and evolved from catecholamines from the adrenal medulla, whereas corticosteroids, from the adrenal cortex, are by far the most effective controllers of the underlying inflammatory process in the airways. The current 'gold standard' of asthma therapy is a combination inhaler containing a long-acting beta(2)-agonist with a corticosteroid - an improved form of adrenal gland extract. Cromoglycate, derived from a plant product and theophylline, a dietary methyl xanthine, have also been extensively used in the therapy of asthma, but we still do not understand their molecular mechanisms. Pharmacology has played an important role in improving natural products to make effective long lasting and safe asthma therapies, but has so far been challenged to produce new classes of antiasthma therapy. The only novel class of antiasthma therapy introduced in the last 30 years are leukotriene antagonists, which are less effective than existing treatments. New, more specific, therapies targeted at specific cytokines are less effective than corticosteroids, whereas more effective therapies carry a risk of side effects that may not be acceptable. It seems likely that pharmacology, rather than molecular genetics, will remain the main approach to the further improvement of treatment for asthma.

Short-acting beta-agonist research: a perspective. 1997.

Asthma mortality increased sharply in New Zealand in 1977, prompting a national investigation into circumstances of asthma deaths. Subsequent observations of improved asthma control in subjects withdrawn from regular beta(2)-agonist treatment raised the question of whether asthma severity and, therefore, mortality could relate to frequent beta-agonist use. A randomized controlled trial of regular inhaled fenoterol versus as-needed bronchodilator use showed worsened asthma control during regular treatment despite concomitant use of inhaled corticosteroids. Assessment of these findings led to delay in the publishing of the American Asthma Guidelines, which were modified to suggest caution in using beta(2)-agonist treatments. Simultaneously, case control studies in New Zealand suggested that prescription of fenoterol was a substantial risk factor for asthma mortality. The causal association was hotly debated, but increasing evidence pointed to an adverse effect of fenoterol on asthma severity and, hence, mortality. This was supported by dramatic decreases in both morbidity and mortality when fenoterol was effectively withdrawn from use in New Zealand. The link between worsening asthma morbidity and mortality, and the use of potent short-acting beta(2)-agonists fulfills the Bradford Hill criteria for attributing causality. Application of evidence from randomized, controlled trials of short-acting beta-agonist use has led to a major shift in therapy in asthma to the recommendation of as-needed use only of short-acting beta-agonists and decreased patient reliance on regular bronchodilator therapy.

Inhaled adrenergic bronchodilators: historical development and clinical application.

The adrenergic bronchodilators that have been developed for oral inhalation represent successive refinement in terms of receptor specificity and duration of action. Beta agonist bronchodilators have durations of 4-6 hours, or, in the case of salmeterol, of up to 12 hours, offering convenient dosing. Inhalation of the aerosol formulations targets the lung directly. The release of levalbuterol now provides an agent with a single isomer active on beta-2 receptors. The currently available agents offer clinicians and patients with reversible obstructive lung disease a choice of sophisticated drugs for airway smooth muscle relaxation. Although improvements in the drugs have reduced adverse effects and beta agonists are considered safe, concerns persist about the effect of beta agonists in asthma. An improved understanding of asthma pathophysiology may lead to more appropriate use of beta agonists in asthma.

The evolution of beta-agonists.

Inhaled beta-agonists have become the mainstay of bronchodilator therapy for reactive airway diseases, either alone or in conjunction with other medications. The history of the development of beta-agonists is a fascinating one that spans more than 5000 years. Scientific investigation for the past several hundred years has elucidated the physiology of bronchoconstriction and bronchodilation. In the past decade, a wealth of knowledge has come forth since the discovery of the beta-adrenoceptor which, along with advances in pharmacology, have helped answer the questions of how beta-agonists work. From these advancements, three classes of beta-agonists have been developed: catecholamines, resorcinols, and saligenins. The chemical structures of the more commonly used agents in each class, their interaction with the beta-adrenoceptor, and their beneficial and adverse effects are discussed. Review of the duration of action of these agents may suggest a new way of classifying them into ultrashort-acting, short-acting, intermediate-acting, and long-acting.

[Astute in vivo observations discover anti-asthma medication]. / Skarpsinniga in vivo iakttagare upptäcker astmaläkemedel.

Will the new reductive biology write the book of revelation of all progress as concerns the pathophysiology and pharmacology of asthma? The early and recent medical history of anti-asthma drugs supports the possibility that exploratory in vivo research involving patients and disease-like test systems may "unexpectedly" provide leap discoveries in pathophysiology and pharmacology. New treatments based on defined molecular disease mechanisms will no doubt emerge. However, the future may also hold novel important anti-asthma drugs where the exact mode of action remains a challenge. Indeed, many aspects of the efficacies of the already long established anti-asthma drug principles have yet to be explained at the end-organ, cellular and molecular levels.