Plasma hyaluronan levels in rabbit immobilization osteoarthritis: effect of remobilization

The right knee joint of 11 rabbits was immobilized in full extension with a splint for a period of three days. The effect of the immobilization and subsequent remobilization on plasma hyaluronan (HA) level was measured, using a sensitive radiometric HA binding protein (125I-HABP) assay. No significant effect of the immobilization on plasma HA level (54 +/- 4 micrograms/l) was noted, but shortly (45 minutes) after splint removal, plasma hyaluronate was at its highest (91 +/- 20 micrograms/l). One day after removal of the splint a return to baseline (53 +/- 6 micrograms/l) was observed. It is suggested that HA may accumulate in the joint during immobilization. Shortly after removing the splint, the level of HA shows a rise in many of the rabbits, even if this is not a consistent finding, probably due to variation in the extent and kinetics of the HA mobilization. Such an accumulation of HA could be deleterious for joint tissues, since HA is an-effective stimulator of interleukin-1 (also called catabolin) synthesis and secretion, and since immobilization osteoarthritis ensues in the splinted rabbit joints.