HISTOCHEMICAL CHARACTERIZATION OF THE AGING MICROVASCULATURE IN THE HUMAN AND OTHER MAMMALIAN AND NONMAMMALIAN VERTEBRATES BY THE PERIODIC ACID-SCHIFF REACTION

Prior histochemical studies with the periodic acid-Schiff (PAS) reaction have shown altered biochemical composition in a limited part of the microvasculature (MV) in aging in two species of laboratory animals. We therefore studied, with the PAS reaction, all the components of the MV in multiple tissues from various immature, adult and aged mammals, including human, and immature and aged non-mammalian vertebrates. We now demonstrate that there is an altered biochemical composition of capillaries, arterioles and venules in various tissues with aging. These are first detectable somewhat beyond half the life-span in man ( > 45 years), marmoset (5 years) and dog (8 years) and seen in old fish, reptiles and birds. The capillary wall is increasingly PAS+; in arterioles there are focal PAS+ areas in the media which increase in size and number with age and become hyalinized masses. The non-muscular venules are increasingly PAS+ apparently due to a polysaccharide staining of connective tissue elements. These histochemical changes in the MV with aging are in the extracellular matrix and appear to be a specific manifestation of aging in vertebrates. The consequences of such changes in MV aging may be important physiologically.