Methods

Albino rats of Mendel-Osborne strain, 5 weeks old, were purchased from a commercial breeder. During the first week, tracheal constriction was done, and intratracheal injection initiated. The rats were fed a commercially available diet and were weighed once a week. After seven to 12 weeks they were anesthetized for measurement of pulmonary function, collection of blood samples and the rat was subsequently sacrificed. The histological section from the lung was prepared and assessed for emphysematous lesions. The details of each major procedure are as follow: Tracheal Constriction.-The rat was anesthetized with ether and the trachea was exposed by a midline neck incision. An 00 silk suture was tied around the trachea to fit snugly around the circumference. The skin was sutured with silk thread. Intratracheal Injection.-A miniature laryngoscope, similar to that described by Gross6 was used to facilitate the injection of either saline or 0.1% crystalline papain. The injection was administered once a week; during the first two weeks, the volume of injection was 0.5 ml and this was increased to 1 ml during the next two weekly injections. An IS-gauge, 3-inch needle with beveled tip was inserted into the larynx with the animal under light ether anesthesia. A miniature bulb was mounted to the tip of the speculum to give direct illumination of the laryngeal cord.