5-HT modifiers as a potential treatment of asthma

ATP stimulates Ca2+ oscillations and contraction in airway smooth muscle cells of mouse lung slices

In airway smooth muscle cells (SMCs) from mouse lung slices, > or =10 microM ATP induced Ca2+ oscillations that were accompanied by airway contraction. After approximately 1 min, the Ca2+ oscillations subsided and the airway relaxed. By contrast, > or =0.5 microM adenosine 5'-O-(3-thiotriphosphate) (nonhydrolyzable) induced Ca2+ oscillations in the SMCs and an associated airway contraction that persisted for >2 min. Adenosine 5'-O-(3-thiotriphosphate)-induced Ca2+ oscillations occurred in the absence of external Ca2+ but were abolished by the phospholipase C inhibitor U-73122 and the inositol 1,4,5-trisphosphate receptor inhibitor xestospongin. Adenosine, AMP, and alpha,beta-methylene ATP had no effect on airway caliber, and the magnitude of the contractile response induced by a variety of nucleotides could be ranked in the following order: ATP = UTP > ADP. These results suggest that the SMC response to ATP is impaired by ATP hydrolysis and mediated via P2Y(2) or P2Y(4) receptors, activating phospholipase C to release Ca2+ via the inositol 1,4,5-trisphosphate receptor. We conclude that ATP can serve as a spasmogen of airway SMCs and that Ca2+ oscillations in SMCs are required to sustain airway contraction.

The medical benefit of 5-HT research

5-HT research is now more than 50 years old, and it has generated a wealth of therapeutic agents, some of which have had a major impact on disease management. The 5-HT reuptake inhibitors (SSRIs) are among the most widely prescribed drugs for treating depression and a variety of other disorders including anxiety, social phobia and premenstrual dysphoria (PMD). The other major success stories of 5-HT research are the discovery of 5-HT1B/D receptor agonists for treating migraine and 5-HT3 receptor antagonists for chemotherapy and radiation-induced emesis. The role of 5-HT in the mechanism of action of antipsychotic agents remains a topic of intense research, which promises better treatments for schizophrenia in the future. Compounds interacting with 5-HT1F, 5-HT2C, 5-HT6 and 5-HT7 receptors are currently under investigation and may prove to have important therapeutic applications in the future.

The pharmacologic treatment of uncomplicated arterial hypertension in patients with airway dysfunction

Because many antihypertensive drugs can affect airway function, the treatment of hypertension in patients with airway dysfunction is complex. For example, the worsening or precipitation of asthma by beta-adrenoceptor antagonists is well-recognized, but beta(1)-adrenoceptor blockers that exert mild beta(2)-agonist effects, and those that modulate the endogenous production of nitric oxide, affect airway function to a lesser extent. Therapy with selective alpha(1)-blockers is not contraindicated in cases of chronic airway obstruction. Conversely, alpha(2)-agonists must not be given to asthmatic subjects because they can adversely affect the bronchi. Calcium channel blockers do not exert severe side effects on the airways. Angiotensin-converting enzyme inhibitors may cause cough and exacerbate or even induce asthma; however, angiotensin II type I (AT(1)) antagonists do not cause cough. 5-Hydroxytryptamine modifiers such as urapidil are a treatment option for patients with chronic airway obstruction. In patients with airway dysfunction, we suggest treatment with thiazide diuretics as the initial drug choice, and calcium channel blockers if the response is poor. In the case of no response, calcium channel blockers alone must be used. However, there is no strict rule because individual patients may respond differently to individual drugs and drug combinations. Consequently, it is important to adopt a flexible approach. For patients who are unresponsive to the aforementioned drugs, AT(1) receptor antagonists, newer beta(1)-adrenoceptor-blocking agents with ancillary properties (eg, celiprolol or nebivolol), and/or vasodilators can be considered.