The impact of prolonged general anaesthesia on composition of glycosaminoglycans (GAGs) components of pulmonary extracellular proteoglycans (PGs) was studied in 20 healthy rats anesthetized with ketamine/medetomidine (K) or urethane/penthobarbital (U) given i.p. After tracheotomy and cannulation of the carotid artery, the animals were turned supine and left to breath spontaneously for either 15 min [sham controls; K-s (n=5) and U-s (n=5) groups] or 4 hours [K-4h (n=5) and U-4h (n=5) groups]. At the end of experiments, analysis of GAGs were performed on excised lung tissue samples. In U-4h, the lung static pressure-volume curve was shifted to the right compared to K-4h, with a significantly decrease of static compliance. The extravascular lung water content was within normal values in all groups, independently upon the type of anesthesia. However, in U-4h lungs the extraction of loosely bound chondroitin sulphate (CS) GAGs and, in particular, of heparan sulphate (HS) GAGs was significantly increased with respect to sham and to K-4h groups. The greater GAG extraction was associated with increased expression of systemic and local metalloproteases both in their zymogen (pro-MMP-9 and pro-MMP-2, respectively) and activated (MMP-2, MMP-9) forms. Therefore, the anaesthetic drug chosen to induce prolonged general anaesthesia may have a profound effect on the pulmonary function, modifying not only the respiratory pattern, but also the integrity of the lung parenchyma.