The circulation of the airways: anatomy, physiology and potential role in drug delivery to the respiratory tract

Comparison of the bronchodilating effects of inhaled β₂-agonists after methacholine challenge in a human lung reperfusion model

The aim of the present investigation was to compare the onset of action and intrinsic activity of the long-acting β(2)-agonist GW597901 with the fast- and short-acting salbutamol as model compounds using an isolated human lung reperfusion model. Twelve resected human lung lobes were challenged with methacholine (MCh) and subsequently nebulised with either GW597901 or salbutamol. Prostaglandin E(2) (PGE(2)) concentrations in the perfusion fluid were compared with the dose of MCh that was required to induce a bronchoconstriction. After successful MCh provocation, nebulisation of GW597901 and salbutamol fully reversed any observed bronchoconstriction. The bronchodilating effect was more pronounced for GW597901. Salbutamol revealed an immediate onset of action while the effect of GW597901 was observed with an approximate delay of 6 min. Higher doses of MCh were required for a successful bronchial challenge in the presence of elevated PGE(2) levels (r=0.8171, p ≤ 0.05). For the first time, an isolated perfused human lung model has been established for comparing the onset of action and potency of a short- and long-acting β(2)-agonist. We therefore conclude that it is an alternative for determination of drug effect characteristics and suitable for supplementing or predicting clinical data.

Clinical perspectives: role of the airway circulation in drug therapy

Theoretically, the airway circulation can regulate the absorption of inhaled drugs, redistribute inhaled drugs within the respiratory tract, and influence the distribution of systemic drugs to the airway. Some of these functions of the airway circulation have been verified experimentally, but not in human subjects. Since pharmacological manipulation of airway blood flow could have therapeutic implications in airway disease, the development of new methods to measure airway blood flow noninvasively in human subjects is needed.