Recent advances of knowledge on the mechanism of action of drugs modifying the bronchial secretions.

In order to explain the mechanism of action of drugs modifying the bronchial secretions, their subdivision into agents with a direct or an indirect action seems justified: the former primarily modify already formed secretions, whilst the latter act on the bronchial structures originating mucus. In hypersecretive states with increased viscoelasticity of mucus, a widespread therapy is represented by the use of direct reducing drugs, which act by breaking the mucofibrillar network. Among them the most important are those with free sulphydryl groups (-SH), which can break the disulphide bonds of the bronchial secretions. The mechanism of action of substances such as acetylcysteine and tiopronin, that are included in those with a direct reducing action, was already verified by researches with the modified thrombo-elastograph (MTE) and has been recently confirmed by the present authors by employing a simple biochemical method, by which the action of such drugs on the structure of serum IgM can be studied in vitro. The same method permits the classification of carbocisteine and letosteine as amongst the drugs with indirect action. From the results obtained by such in vitro experiences, the necessity to examine more closely the consequences of secondary effects which direct mucolytic agents may cause by modifying the rheological, biochemical and immunological properties of bronchial secretions has been demonstrated.