TURNOVER OF HYALURONAN IN SYNOVIAL JOINTS - ELIMINATION OF LABELED HYALURONAN FROM THE KNEE-JOINT OF THE RABBIT

After the injection of [H-3]acetyl-labelled hyaluronan into normal rabbit knee joints, about 90% of its isotope content was ultimately accounted for as (H2O)-H-3. The rate of elimination of hyaluronan from synovial fluid was therefore estimated from changes in the level of (H2O)-H-3 in plasma. The half-life of plasma (H2O)-H-3 was 6.2 days (S.D. 0.7). As estimated from its metabolism to (H2O)-H-3, the mean intrasynovial half-life of [H-3]hyaluronan of high molecular weight (modal relative molecular mass (M(r)) > 6.0 x 10(6)) was 13.2 h (range 11-15.5 h; n = 4); an otherwise identical preparation of low molecular weight (modal M(r) 0.09 x 10(6)) exhibited a mean half-life of 10.2 h (range 7.8-13.5 h; n = 4). The difference between the two groups was significant (P = 0.029). Both estimates were nevertheless close to those determined by others in the same species for injected proteoglycans (M(r) 2.5 x 10(6), t1/2 = 12 h) and for endogenous hyaluronan calculated from changes in concentration during intravenous infusion of fluid under anaesthesia (t1/2 = 16 h). The similarity suggests that hyaluronan and proteoglycan are removed from synovial fluid by a common pathway with limited dependence on their molecular dimensions and concentrations.