Effects of albuterol enantiomers on in vitro bronchial reactivity.

Abstract

Asthma is one of the most common diseases in the industrialised countries. The underlying mechanisms are complex and still not fully understood although inflammation of the airways plays an important role. There are to day several types of drugs used in the treatment of asthma such as anti-inflammatory drugs, specific antagonists for inflammatory mediators and bronchodilators. Beta-agonists are the main choice for relaxing airway constriction, however unwanted effects of beta-agonists on patients with asthma has been reported. The betaantagonists that are used for treatment of hypertension and various other conditions also is shown to be deleterious in asthmatics. In the present study we have used guinea pig airways to examine the proposed deleterious effects of beta-agonists and antagonists. We have shown that the (S)-enantiomeric forms of salbutamol and formoterol are able to potentiate cholinergic stimuli and we have shown that the potentiation was indomethacin sensitive in airway preparations of sensitised guinea pigs. We also showed and confirmed that the (R)-enantiomeric forms of salbutamol and formoterol were more potent in relaxing airway smooth muscle contracted with different stimuli compared to the (S)-enantiomers. The betaantagonists propranolol and pindolol were shown to be able to contract tracheal preparations if they had been pre-treated with a beta-agonist and the contraction was not simply a blockade of the beta-adrenoceptor induced relaxation. Propranolol contraction was stereo-selective and (S)-propranolol was more effective in inducing contraction than (R)-propranolol. Moreover, atenolol a betacselective antagonist induced significantly smaller contractions compared to general beta-antagonists. This indicates that the beta2-adrenocepor probably is involved in the beta-antagonist induced contraction. The cyclooxygenase inhibitor indomethacin, the 5-lipoxygenase inhibitor MK886 and a thromboxane A2 antagonist as well as capsaicin reduced the beta-antagonist induced contraction. This indicates that several arachidonic acid products as well as neuropeptides may be involved in the beta-antagonistinduced contraction.The worsening of asthma by beta-antagonists is well known and the risks associated with beta-agonists are discussed, but the mechanisms behind these effects need further clarification. In this thesis some of the possible mechanism have been discussed, further studies are needed in order to get more safe and effective asthma treatment regime.