Antitussive Effect of Diltiazem in Experimental Conditions

Bratisl Lek Listy 2004; 105 (56): 203206 203

EXPERIMENTAL STUDY

Antitussive effect of diltiazem in experimental conditions

Franova S, Nosalova G

Department of Pharmacology, Jessenius Faculty of Medicine, Comenius University, Martin, [email protected]

Abstract

Background: Cough is the most important defence reflex of the airways. Little information exists about participation of the ion channels in the mechanism of the cough reflex. Objectives: The aim of the study was to investigate the effect of diltiazem administration on the sensitivity of the mechanically induced cough reflex in experimental conditions. Methods: Mechanical stimulation of the laryngopharyngeal and tracheobronchial area of the airways in non-anaesthetized cats was used in this experiment. The number of cough efforts, and the frequency and intensity of the cough attack were utilized as evaluated parameters. Results: Perorally administered diltiazem (30 mg/kg b.w.) caused a statistically significant decrease of measured cough parameters. Cough suppressing activity of diltiazem was lower than codeine, but higher than dropropizine and prenoxdiazine. Conclusion: Experimental results showed antitussive activity of the calcium-channel blocker diltiazem and suggested the role of voltage-gated calcium channels of type L in mechanism of the cough reflex. (Fig. 4, Ref. 15.) Key words: cough, diltiazem, calcium channels of L-type.

The cough, as the most frequent symptom of respiratory sys- propriate coughing in response to stimuli and mediators that are tem diseases, is the important defence reflex of the airways. The otherwise only mildly irritating (7). RARs are more sensitive to neuro-anatomical components of the cough reflex include sub- mechanical events occurring in the airways (8). The cough reflex sets of sensory nerve fibres innervating the airways, which de- is precipitated by distinct firing patterns in RARs fibres. Neuropep- tect the presence of either mechanical or chemical irritation of tide-containing airway C-fibres are much less sensitive to mechani- the airways. The airways are innervated by population of affer- cal stimuli, but are activated in response to a variety of chemical ent nerves including myelinated Aä and unmyelinated C-fibres irritants (cigarette smoke, bradykinin, tachykinins etc.) (9). (1). These sensory nerves project to the nucleus of the solitary The experimental studies provide new information about the tract (nTS) in the brainstem and drive a complex neuronal net- peripheral and central mechanism of the cough reflex, however work that integrates and coordinates coughing (2). The efferent very little is known about function of ion channels in modula- nerves project from the central nervous system to a variety of tion of the cough. The aim of our experimental study was to effector muscles responsible for producing the cough (3). follow the participation of the L-type calcium VOC (voltage In the afferent mechanism of the cough reflex three types of operated channel) in mechanism of the cough reflex. The effect sensory receptors may be involved: rapidly adapting (RARs), C- of diltiazem administration on the sensitivity of the mechani- fibre, and Aδ-nociceptors (4). While all three types of receptors cally induced cough in non-anaesthetized cats was investigated are activated with various sensitivities by tussigenic agents, RARs in the experiment. cause cough directly and C-fibre receptor act by local release of tachykinins that stimulate RARs (5). The reflex role of Aδ-noci- Department of Pharmacology, Jessenius Faculty of Medicine, Comenius ceptors is unknown (6). University, Martin The neural pathway responsible for regulating cough may un- Address of correspondence: S. Franova, RND, PhD, Dept of Pharma- dergo disease-related changes (plasticity) such that the protective cology JMF CU, Sklabinska 26, SK-037 53 Martin, Slovakia. aspects of the cough reflex are replaced by exaggerated and inap- Phone: +421.43.4132535, Fax: +421.43.4134807 204 Bratisl Lek Listy 2004; 105 (56): 203206

Methods and methods

Diltiazem, codeine and dropropizine were purchased from Sigma-Aldrich. All other chemicals and solvents used were purchased from commercial sources.

Mechanically induced cough by in vivo method A method of mechanical stimulation of the laryngopharyngeal and tracheobronchial area of the airways of the non-anaesthetized cats of both sexes weighing 15002500 g was used in the experiment. After several days of quarantine, a tracheal can- nula was surgically implanted into the animals, which served for the mechanical stimulation of the airways with nylon fibre 0.35 mm in diameter, as well as for recording of side tracheal pressure. The cough parameters included: the number of cough efforts (NE), the frequency of the cough (NE/min), and the intensity of the cough efforts in expirium (IE+) and inspirium (IE-) were evaluated on the basis of the pressure values recorded during the experiment from laryngopharyngeal (LPh) and tracheo- Fig. 1. The changes in the number of cough efforts (NE) from laryn- bronchial (TBr) part of the airways. gopharyngeal (LPh) and tracheobronchial (TB) area of the airways The number of the cough efforts obtained before drug ad- of the non-anaesthetized cats, before diltiazem administration (control) and after 0.5, 1, 2, 5 hours after diltiazem administration. Data ministration represented the control values. Diltiazem was ad- represent the mean S.E.M., n=12, * p<0.05, ** p<0.01. ministered perorally as a saline solution in the dose 30 mg/kg b.w.. The cough suppressing effect of diltiazem was compared to effect of clinically used antitussives codeine (10 mg i.p.), dropropizine (30 mg i.p.) and prenoxdiazine (50 mg i.p.). The effect of diltiazem on the cough parameters was monitored in the intervals 0.5, 1, 2, 5 hours after administration. Statistical analysis: The results of the experiments, which estimated the cough response, were evaluated by Wilcoxon Wilcox statistical method. The columns represent the average values; the dispersion is mean error of average. Statistical sig- nificance * p<0.05, ** p<0.01.

Results

The cough suppressing effect of diltiazem was investigated after mechanical stimulation of the laryngopharyngeal (LPh) and tracheobronchial (TBr) area of the airways in non- anaesthetized cats. Diltiazem in the dose 30 mg/kg b.w. administered perorally caused a statistically significant decrease in the number of cough efforts (NE) (Fig. 1) from laryngopharyngeal as well as from the Fig. 2. The changes in the frequency of the cough attacks (NE/min) tracheobronchial area of the airways. from the laryngopharyngeal (LPh) and tracheobronchial (TB) regions A similar picture of the changes was observed after estimation of the airways of the non-anaesthetized cats, before diltiazem admin- of cough frequency (NE/min) from LPh and TBr region (Fig. 2). istration (control) and 0.5, 1, 2, 5 hours after diltiazem administra- Significant suppression of the other measured cough param- tion. Data represent the mean S.E.M., n-12, * p<0.05, ** p<0.01. eter the intensity of the cough attacks in expirium (IE+) and inspirium (IE-) from both parts of the airways was observed after diltiazem application (Fig. 3). parameters was compared to drugs generally used in clinical prac- The cough parameters were suppressed significantly, within tice to suppress the cough reflex: opioid antitussive codeine and 30 minutes after administration of diltiazem and the decrease peripherally-acting prenoxdiazine or dropropizine (Fig. 4). The was sustained throughout the experiment. antitussive efficiency of diltiazem (40.4 %) was lower than the In order to recognize the importance of the observed antitus- effect of codeine (61.8 %), but significantly higher than dro- sive activity of diltiazem, the effect of diltiazem on the cough propizine (27.3 %) and prenoxdiazine (24.7 %). Franova S, Nosalova G. Antitussive effect of diltiazem 205

However limited information exist about the modulation of the cough reflex through the ion channels. Local anaesthetics and other inhibitors of voltage-gated sodium channels block the cough reflex (12). Pinacidil, an ATP-sensitive K+ channel opener, in- hibited the cough in guinea pigs (13). The openers of maxi-K+ Ca2+ dependent channel of the afferent nerves are the other group of substances able to inhibit the cough reflex (14). Our experimental results, related to the cough suppressing activity of calcium channel blocker diltiazem, confirmed the participation of voltage-operated calcium channels of type L in the modulation of the cough reflex. In order to recognize the importance of the observed antitussive activity of diltiazem, we performed comparative experiments with some drugs generally used in clinical practice: the opioid antitussive codeine and the non-opioid peripherally acting dropropizine and prenoxdiazine. It is evident from the experiment that the cough-suppressing activity of diltiazem was lower than that of the most frequently used opioid antitussive drug codeine, however the results of our study showed that diltiazem had a greater antitussive effect than non-opioid dropropizine and prenoxdiazine. The mechanism of the cough-suppressing activity of diltiazem could involve the peripheral or central level. The voltage-gated calcium current plays an important role in the excitability of the vagal afferent nerves (15). The antitussive effect of diltiazem can be a result of its ability to inhibit the activity of the peripheral nerve endings of C and Aδ fibres regulating the cough reflex. The modulation of the central transmission of cough reflex Fig. 3. The changes in the intensity of cough attacks in expirium in the nucleus tractus solitarius (nTS) of the brainstem could be (IE+) and in inspirium (IE-) from the laryngopharyngeal (LPh) and another location where the calcium channel blockers might act. tracheobronchial (TB) areas of the airway of the non-anaesthetized In conclusion, the present study demonstrates the cough sup- cats, before diltiazem administration (control) and 0.5, 1, 2, 5 hours pressing activity of the calcium channel blocker diltiazem on after diltiazem administration. Data represent the mean S.E.M., mechanically induced cough under experimental conditions. The n=12, * p<0.05, ** p<0.01. results confirmed the role of calcium channels of type L in the mechanism of the cough reflex. From this point of view the abil- Discussion ity of diltiazem to suppress the cough reflex is clinically rel- evant and physician should be take this pharmacodynamic ac- Airway afferent (sensory) nerves express a variety of recep- tivity into account during therapeutic use of diltiazem. tors and ion channels that, when acted upon by various pharma- cological agents, modulate the activity of these nerves (10). The induced changes in the activity of airway afferent nerves, in turn, inform the central nervous system about a change in their imme- diate environment, and via reflex pathways modulate the para- sympathetic (cholinergic and noncholinergic) and sympathetic outflow to the airways (11). In addition, airway afferent nerve activation is responsible for initiating the cough reflex and serves to modulate breathing pattern. According to our results the voltage operated (gated) calcium channels type L play a role in the reflex mechanisms of the cough. Diltiazem administered perorally caused in our study a significant decline in the measured cough parameters induced by mechanical stimulation of the laryngopharyngeal and tracheobronchial mucous membrane of the airways in non-anaesthetized cats. Ion channel modifying compounds can increase or decrease Fig. 4. Comparison of the antitussive efficiency of diltiazem (30 mg/kg ionic current through voltage-gated ion channels in airway affer- p.o.) to antitussives used in clinical practice /- codeine (10 mg/kg ent nerves and in this way change the respiratory reflex activity. i.p.), prenoxdiazine (50 mg/kg i.p.) and dropropizine (30 mg/kg i.p.). 206 Bratisl Lek Listy 2004; 105 (56): 203206

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