The composition of the nucleus from 25 intervertebral discs of sperm and fin whales of different fetal developmental stages and postnatal ages is reported. Early stages in the nucleus intrauterine life (one quarter to one half development) show drastic changes in the proportion of galactosamine and glucosamine. The collagen content of the dry fetal nucleus is higher than the hexosamine content in early stages although it rapidly decreases to a plateau in specimens of one half to full term development. Afterward, in the postnatal nucleus and during aging, the amount of hexosamine greater than that of collagen on a dry weight basis; furthermore, both remain invariant, although irregular changes in the proportion of galactosamine and glucosamine are observed.
The polysaccharides from the fetal tissue are more polydisperse and undersulfated than those isolated from postnatal specimens. The major polysaccharides of the whale nucleus are CS-4SO4, CS-6SO4, and KS. The fetal nucleus also contains CS. The distribution of CS-4SO4 and CS-6SO4 in the cartilage plates is the reverse of that observed in the nucleus pulposus. Characteristic of both anatomic structures is a decrease of CS during fetal development.
The proteoglycan fraction of the postnatal nucleus (PG-L) was found to contain polysaccharide peptides. Similar fractions from fetal specimens contained no polysaccharide peptides. The polydispersity of the proteoglycans in the fetal nucleus appears to be regulated by the amount of a cystine-containing proteoglycan fraction (Fraction F) sensitive to disulfide reducing reagents. Such a correlation was not observed in preparations from postnatal specimens