Diffusion of small solutes into the intervertebral disc: as in vitro study

By comparing results obtained in vivo on penetration of (35S) sulphate and (3H) methyl glucose into the intervertebral disc of adult dogs, with those calculated using Fick’s law, and diffusion and partition coefficients obtained in vitro, diffusion was shown to be the main mechanism for transport o f small solutes into the intervertebral disc. About 40 percent of the endplate area was found to be permeable to small solutes. However the amount of solute entering via the endplate was shown to be less for negatively charged solutes such as the sulphate ion, than for neutral solutes such as glucose, because of charge exclusion in the region of the nucleus. The mean turnover time of 470 days found for sulphated glycosaminoglycans in the disc is similar to that reported for dog articular cartilage.