Drug targeting of airway surface liquid: a pharmacological MRI approach

Pharmacological MRI at 4.7 T was used to investigate the secretory response to Sylvestris pine oil stimuli in the rat airways, with the aim of developing an in vivo model in a small laboratory animal. The availability of such a model would greatly facilitate the drug discovery process using compounds active on airway surface liquid (ASL) production, and would make it possible to obtain information on chemoreceptoral mechanisms and to test the effects of environmental substances on the airways. T1- and T2-weighted images were acquired in the trachea and larynx before and at various times after exposure to pine oil. Several post-processing procedures were tested in order to improve the visibility of the secretory response and to measure the enhancement of the signal intensity of ASL. A semiautomatic application software was written to localize and to measure the volume involved in the secretory response to a compound administration. A significant effect of the pine oil administration on the secretory response was founded in trachea (p<0.01) and in the salivary glands (p<0.01). 3D reconstructions of MRI data and virtual endoscopy permitted a quick visualization of tracheal morphology and localization of the greatest response to stimulus. The study demonstrated that, despite technical problems due to the air/tissue interface and to the small dimensions of the experimental animals, the secretory response can be evaluated and the pharmacological MRI (phMRI) of the rat airways is feasible. The potential and the limitations of phMRI investigation in drug targeting of ASL are discussed.