Isolation of rat trachea interstitial fluid and demonstration of local cytokine production in lipopolysaccharide-induced systemic inflammation.

Access to interstitial fluid from trachea is important for understanding tracheal microcirculation and pathophysiology. We tested whether a centrifugation method could be applied to isolate this fluid in rats by exposing excised trachea to G forces up to 609 g. The ratio between the concentration of the equilibrated extracellular tracer 51Cr-labeled EDTA in fluid isolated at 239 g and plasma averaged 0.94 +/- 0.03 (n = 14), suggesting that contamination from the intracellular fluid phase was negligible. The protein pattern of the isolated fluid resembled plasma closely and had a protein concentration 83% of that in plasma. The colloid osmotic pressure in the centrifugate in controls (n = 5) was 18.8 +/- 0.6 mmHg with a corresponding pressure in plasma of 22 +/- 1.5 mmHg, whereas after overhydration (n = 5) these pressures fell to 9.8 +/- 0.4 and 11.9 +/- 0.4 mmHg, respectively. We measured inflammatory cytokine concentration in serum, interstitial fluid, and bronchoalveolar lavage fluid in LPS-induced inflammation. In control animals, low levels of IL-1 beta, IL-6, and TNF-alpha in serum, trachea interstitial fluid, and bronchoalveolar lavage fluid were detected. LPS resulted in a significantly higher concentration in IL-1 beta and IL-6 in interstitial fluid than in serum, showing a local production. To conclude, we have shown that interstitial fluid can be isolated from trachea by centrifugation and that trachea interstitial fluid has a high protein concentration and colloid osmotic pressure relative to plasma. Trachea interstitial fluid may also reflect lower airways and thus be of importance for understanding, e.g., inflammatory-induced airway obstruction.