Effects of aging on the synthesis of antithrombin-binding sites on heparin chains and heparan sulphate chains in the rat.

[35S]Heparin proteoglycans were isolated from the skins and peritoneal mast cells of male rats aged 2 to 22 months. Their [35S]heparin chains were separated on antithrombin-agarose into fractions with high and low affinities for antithrombin. In skin, the proportion of 35S-labelled high-affinity heparin chains declined from 23% at 2 months to 8% at 12 months and did not change significantly between 12 and 22 months. In peritoneal mast cells, the proportion of 35S-labelled high-affinity heparin chains increased from 14% at 2 months to 21% at 4 months and then did not vary significantly until 15 months of age. By 21 months a consistent and significant decline to 8% occurred. The structures of high-affinity heparin proteoglycans did not change with age. Their decreased proportions, without change in their structure, may indicate that they are produced by a unique subset of mast cells, the proportion of which declines with age. [35S]heparan sulphate chains were isolated from skins and brains of rats in the same age range and fractionated on antithrombin-agarose. There were no significant variations in the proportions of 35S-labelled high-affinity heparan sulphate chains in skin (10%) or brain (24%) between 4 and 22 months of age.