The composition and protein metabolism in the immature rabbit intervertebral disc

The nucleus pulposus (NP) and annulus fibrosus (AF) of immature rabbit intervertebral discs (IVD) have been subjected to the dissociative extraction procedure of Sajdera and Hascall (1969). The soluble, insoluble and unextracted fractions so obtained were analysed for total nitrogen, collagen, tyrosine, uronic acid, hexosamine and sialic acid content. A high proportion of non-collagenous protein, hexose and sialic acid in the NP insoluble fraction suggests the presence of glycopeptides associated with collagen and/or proteoglycans. The levels of proteoglycan in the soluble NP and AF fraction are similar. Immature (soluble) collagen, however, resides largely in the AF region. The metabolism of rabbit IVD protein components was also investigated both chemically and by autoradiography. L-Tyrosine-3,5-H3 was administered intraperitoneally (3 mc/kg) to 4 week-old rabbits. Animals were sacrificed at various time intervals and the harvested tissues extracted as before and lumbar discs collected. The levels of L-Tyrosine-3,5-H3 in the NP and AF insoluble and soluble fractions were determined using a tritium scintillation counting procedure and localisation by autoradiography. Pronounced extracellular activity of proteoglycan and glycoprotein is not evident before 24 hours. Soluble collagen, however, is synthesized and dispersed within 4 hours of isotope administration.