Reduced in vivo plasma fibronectin content of lung matrix during postoperative sepsis

Sepsis after surgery, trauma, or burn contributes to altered lung endothelial permeability and respiratory failure. Fibronectin (Fn), an opsonic and adhesive glycoprotein, exists in both a soluble form in plasma and an insoluble form in the extracellular matrix (ECM). Recent studies [E. M. Wheatley, P. J. McKeown-Longo, P. A. Vincent, and T. M. Saba, Am. J. Physiol. 265 (Lung Cell. Mol. Physiol. 9): L148-L157, 1993] suggest that the ECM content of Fn may influence lung vascular permeability. We evaluated the incorporation of plasma-derived Fn (pFn) into the ECM of the lung during postoperative sepsis. Postoperative nonseptic and postoperative septic rats were compared, using a model of laparotomy followed by cecal ligation and puncture. To label the pFn pool, rats received intravenously 3 micrograms of purified rat 125I-labeled Fn/100 g body weight 6 h after surgery (laparotomy). 125I-Fn in the deoxycholate detergent-insoluble fraction of tissues was used to quantify matrix-incorporated Fn at 4 h after infusion with 125I-Fn. Septic rats exhibited a peripheral leukopenia as well as reduction in plasma volume, Fn halflife, and total pFn pool. Incorporation of pFn in the liver and spleen of postsurgical septic rats was not different (P > 0.05) from sham-operated (postsurgical nonseptic) rats, but incorporation was significantly decreased (P < 0.05) in vivo in the lung. However, under controlled in vitro conditions, lung tissue harvested from septic or sham-operated rats demonstrated a similar tissue incorporation of soluble 125I-pFn as well as similar rates of retention/turnover of ECM 125I-Fn, based on pulse-chase experiments. These data suggest that the in vivo inflammatory environment in the lung during postoperative sepsis, which cannot be reproduced in vitro, may alter the Fn content of the ECM of the lung. Such reduced levels of pFn in the lung ECM may be a factor influencing lung vascular integrity during postoperative sepsis.