Morphologic and Biochemical Features Affecting the Antithrombotic Properties of the Inferior Vena Cava of Rabbit Pups and Adult Rabbits

The incidence of venous thromboembolic disease is reduced in children compared with adults. Thromboprotective mechanisms, some of which have already been identified in plasma, must be present in children. Blood vessel walls have important antithrombotic properties that maintain blood fluidity. This is in part due to proteoglycan (PG)-related glycosaminoglycan (GAG) molecules within vessel walls. PGs are macromolecules with covalently attached GAG chains, either chondroitin, dermatan, heparan, or keratan sulfate. The influence of age on the concentration and anticoagulant activities of PGs and GAGs, within vein walls before puberty has not been previously investigated. We hypothesized that developmental differences in vein walls may contribute to the reduced risk of thrombosis in children. We used a rabbit model to examine morphologic and biochemical features of inferior venae cavae (IVCs). We assessed IVC wall morphology, PG distribution, GAG mass, and GAG antithrombin activity. Morphologically, there were only minor differences between pups and adult rabbits' IVCs. However, there was a significant increase in GAGs by mass in IVCs from pups compared with adult rabbits (p = 0.012). In addition the total antithrombin activity (p = 0.04), and especially that of heparan sulfate (p = 0.01) was significantly increased in pups compared with adult rabbits. These results demonstrate important differences in the antithrombotic properties of IVC walls in pups and adult rabbits. In summary, developmental differences in vein wall PG content and activity exist which may contribute to the reduced risk of venous thromboembolism in children. Further characterization of these differences is required.