Observations on the presence of plasma proteins in skin and tendon

Abstract

The presence of plasma proteins in extracts of skin of rat and rabbit and in extracts of tendon of rat, rabbit and ox was demonstrated by electrophoresis and immunological methods. Plasma proteins and serum albumin labeled with I131 were injected into rabbits. Radioactivities of skin extracts or of the albumin fractions of skin were measured at different times after injection and compared with those of corresponding specimens obtained from blood. Similar experiments were also carried out with C14-labeled albumin, C14-labeled antibody and horse-serum albumin. The crude albumin from rabbit skin resembles circulating serum albumin in its electrophoretic behavior, its UV spectrum in acid and alkaline solution, its optical rotation and its instantaneous denaturation with guanidine. Further partition of this fraction by electrophoresis on treated cellulose columns yielded a major fraction which appeared to be identical with serum albumin as judged by its immunological behavior. But the crude albumin contained at least 2 other proteins resembling serum albumin but not identical with it. It is concluded that both tendon and skin contain significant quantities of serum proteins in addition to those present within the blood vessels. The amount present in rabbit skin is approximately 0.7 g/100 g of skin, which is equivalent to 25-30% of that found in circulating plasma. Appreciable variations between animals and other uncertainties have made it impossible to calculate accurately the rate of exchange between skin albumin and circulating albumin. However, the data suggest that about 60% of the skin albumin is replaced every day by circulating serum albumin.