EFFECT OF TETRACYCLINE ON RABBIT PLEURA

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Abstract
Two concentrations of unbuffered tetracycline hydrochloride in sterile water were instilled into the pleural space of normal rabbits to characterize the acute and long-term response of the pleura to this recently advocated sclerosing agent [used for malignant pleural effusions]. Ten rabbits were given 7 mg of low-dose tetracycline (LTCN) per kg of body weight, and 10 received 35 mg of high-dose tetracycline (HTCN) per kg of body weight in 2 ml of sterile water instilled into the right pleural space through an 18-gauge catheter. Ten rabbits were given 2 ml of sterile water and served as control animals. Thoracenteses were attempted serially for 120 h. Five rabbits from each group were killed after 120 h. and the other 5 were killed after 34 days. Both groups of animals given tetracycline developed an acute exudative pleural effusion characterized by increased leukocyte counts, predominance of neutrophils, normal pH and normal glucose. Pleural-fluid leukocyte count (P < 0.01), total protein concentration (P < 0.01) and the percentage of neutrophils (P < 0.01) decreased significantly during 120 h. The mononuclear cell was again the predominant cell in the pleural fluid after 48-72 h. Pleural fluid pH was significantly lower in the group of animals given HTCN (P < 0.05) and after 12 h. correlated inversely with visceral pleural thickness after 120 h. (r [correlation coefficient] = -0.84, P < 0.01). The control animals had a normal pleural space 120 h after instillation. The rabbits, given LTCN showed minimal inflammation, and those given HTCN demonstrated a marked inflammatory response. Visceral pleural thickness was 0.22 .+-. 0.000 mm in the control animals, 0.21 .+-. 0.01 mm in the rabbits receiving LTCN, and 0.42 .+-. 0.05 mm in those receiving HTCN. The pleural fluid pH 12 h after intrapleural administration of tetracycline was the only pleural fluid characteristic to correlate significantly with the production of pleural symphysis (P < 0.01). Tetracycline injures rabbit pleura by producing a protein-rich pleural effusion. The dose used may be a critical factor in determining whether or not pleural symphysis occurs.

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