Evidence for hyaluronan production in the air pouch model in rats

The aim of our work was to investigate the presence of hyaluronan (HA) in the rat air pouch and its behaviour in response to inflammatory stimuli.

HA levels (by a microplate assay) and the leucocyte count were determined in the fluid obtained from air pouches in which acute or subacute inflammation had been induced by the injection of monosodium urate crystals (MSU) or high density polyethylene (HDPE) debris respectively and in relative controls.

In control pouches of both groups, remarkable levels of HA were found; these levels were higher in the very first hours (2475 and 1850 micrograms/l at 6 hrs) and then gradually decreased. In pouches injected with MSU, HA moderately increased (p < 0.001) after 6 hrs, reached a peak after 12 hrs (p < 0.001) and began to taper at 24 hrs (p < 0.001). The leucocyte count was also increased at 6 hrs (p < 0.001), became higher at 12 hrs (p < 0.001) and tapered at 24 hrs (p < 0.001). In the HDPE pouches, HA levels were significantly reduced with respect to controls after 6 hours (p < 0.001), increasing later (p < 0.001) to reach a peak at 24 hrs (p < 0.001), and returning to the original levels, or even below, in the following 72 hours.

These data confirm that the pouch lining produces fair amounts of HA and provide evidence that, in this system, HA levels seem to be influenced by the degree of inflammation even if with variable behaviour in relation to the different characteristics and phases of phlogosis. The present data suggest that the air pouch is a useful experimental model for studies on HA metabolism in either acute or chronic inflammation.