Bone mineral and glycosaminoglycans in newborn and mature rabbits

The relation between bone mineralization and glycosaminoglycans (GAG) was investigated in newborn and mature rabbit diaphyseal bone. Using the density fractionation technique, the bone was separated into fractions of increasing density from 1.4 to 2.3 grams/ml. Each fraction was analyzed by X-ray diffraction to determine the average crystal size. The GAG content of each fraction and of the unfractionated bone was determined by direct extraction and on a few fractions by sequential extraction in guanidine hydrochloride and guanidine/EDTA. There was a decrease in the GAG content with animal age and with increasing fraction density in the newborn rabbit. In one overlapping fraction (2.0-2.1 grams/ml), the GAG content was twice as high in the newborn as in the mature animal. Finally, the crystal size substantially increased from newborn to mature rabbits. Therefore, calcification and maturation of bone is associated with a decrease in the proteoglycan content of the organic matrix.