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The respiratory system serves as a functional gas exchanger and as a defense against perturbing antigens that cause a reflex tracheo-bronchoconstriction which affects homeostasis. In concert with the cardiovascular system, the pulmonary system continually adapts and responds to the demands for oxygen by tissues throughout the body, and pathological abnormalities profoundly deteriorate this function. Airways act reflexly to limit the intrusion of irritating air pollutants that trigger smooth muscle reactivity as in many pulmonary diseases. Tracheo-bronchoconstriction is a common sign in respiratory diseases and can be simulated experimentally in animal models in order to study the underlying mechanisms and to find the proper therapeutic approach. Since airways innervation plays a major role in the mechanism of smooth muscle hyperreactivity, this study was designed to evoke tracheo-bronchoconstriction by different stimuli that alter the autonomic nervous control of the respiratory system. In addition, the respiratory and hemodynamic effects of different classes of known bronchodilators were compared by using induced-bronchoconstriction in anesthetized dogs