Vascular-extravascular exchange of I131 plasma proteins in the rat

Abstract

Rates at which plasma proteins penetrate from the vascular system into extravascular spaces in tissues was measured with I¹³¹-labeled rabbit gamma globulin, rat gamma and beta globulins, and rat albumin. After vascular mixing was complete, as measured with Cr⁵¹-labeled erythrocytes, initial rates of increase in the ratio of tissue radioactivity to plasma radioactivity were used to calculate vascular-extravascular transfer rates; these are reported as grams blood plasma equivalents which penetrate the vascular-extravascular barrier in 1 gm tissue each hour. Transfer rates ranged from 0.06–0.76 for visceral organs to 0.0005–0.005 for tissues such as muscle, fat and skin; the transfer rates were roughly proportional to the vascularity of the tissues. Ratios of tissue to plasma radioactivity reached at equilibrium were used to calculate the amounts of plasma proteins present extravascularly. These protein masses ranged from 0.02 gm plasma equivalents per gm tissue for muscle to 0.13 for skin. Significant differences between the various plasma proteins were found only in the liver, spleen and stomach.