Albumin diffusion measured in an isolated segment of rabbit lung interstitium with a radioactive tracer (125I-albumin) technique was independent of albumin concentration and similar to the free diffusion of albumin in water (Qiu et al, 1998. J Appl Physiol 85: 575–583). We studied the effect of hyaluronidase on the diffusion of albumin. Isolated rabbit lungs were inflated with silicon rubber by way of airways and blood vessels, and two chambers were bonded to the sides of a ∼0.5-cm thick slab enclosing a vessel with an interstitial cuff. One chamber was filled with 2 g/dl albumin solution containing 125I-albumin and 0.02 g/dl hyaluronidase. Unbound 125I was removed from the tracer by dialysis before use. The other chamber filled with Ringer's solution was placed within a NaI(Tl) scintillation detector. Diffusion of tracer was measured continuously for 120 h. Albumin diffusion coefficient (D) and interstitial area (A) were obtained by fitting the tracer-time curve with the theoretical solution of the equation describing one-dimension diffusion of a solute across a membrane. D averaged 5.2 × 10−7 cm2/s for albumin diffusion with hyaluronidase, 20% less than that measured previously without hyaluronidase. Hyaluronidase had no effect on A. Results indicated an interaction between albumin and interstitial hyaluronan that was the opposite of the steric effect on albumin excluded volume measured in solution.
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