Selective appearance of heparin in mammalian tissues during development

The distribution of heparin in tissues of bovine and porcine fetuses of different ages as well as in the adult animals is reported. Heparin is present almost exclusively in the hematopoietic and lymphoid tissues of fetuses (spleen, liver, thymus and lymph nodes), whereas ileum, skin and lung besides lymph nodes and bovine thymus are the heparin-rich tissues in adult animals. The small amount of heparin in fetal tissues, its decrease in porcine liver and spleen, its appearance in skin, ileum and lung, tissues directly exposed to the environment after birth, its preferential localization at the maternal side of the placenta together with other data led to the suggestion that heparin may be involved with defense mechanisms.