A series of novel xanthine-based tricyclic heterocycles in lH-imidazo [4, 5-c] quinolin-4 (5H)- ones was designed, synthesized, and tested as potential active bronchodilators. Inhibition of the Schulz-Dale (SD) reaction-induced contraction in trachea and inhibition of antigen inhalation-induced bronchospasm in passively sensitized guinea pigs served as primary in vitro and in vivo assays, respectively. Simultaneous measurement of acute lethal toxicity ( ...