Phosphodiesterase 4 and tolerance to beta 2-adrenoceptor agonists in asthma.

beta 2-Adrenoceptor agonists provide a mainstay in the treatment of asthma worldwide. However, despite their ability to provide symptomatic relief, chronic or repeated exposure to beta 2-adrenoceptor agonists does not resolve asthmatic inflammation, because of the rapid development of tolerance by pro-inflammatory and immune cells of the lung. The prevailing belief is that tolerance to the so-called non-bronchodilator actions of beta 2-adrenoceptor agonists is largely attributable to direct receptor desensitization mediated by G protein receptor-coupled kinases and/or cAMP-dependent protein kinase. Here, Mark Giembycz suggests another, largely ignored, explanation for beta 2-adrenoceptor desensitization that is based on the accelerated degradation of cAMP by phosphodiesterase.