Continuous simultaneous measurement of plasma protein concentration and hematocrit in the alert rat. A short preliminary report.

A method for continuous plasmapheresis and refractometric determination of the protein concentration of blood circulating in the vascular system of the unanesthetized rat is presented. The method is applied to demonstrate very rapid transvascular fluid exchange during physical activity of the animal, noradrenalin infusions and hemorrhage. Changes of protein concentration are compared with concomitant changes of hematocrit in the hepatic portal vein and the v. cava inferior. Though both parameters invariably change in a parallel fashion, relative variations of protein concentration fall short of hot variations by 50%.