Concentration of Azoproteins in Yolk Sac Placenta of the Rat.

Bovine serum albumin and rat serum albumin were coupled to an azo dye, echt säure blau B to form colored azoproteins. Female rats at various stages of gestation were exposed 24 hours to these compounds and to control solutions. Both azoprotein molecules could be found within the kidney tubules, lymph nodes, maternal serum, and in all stages of the developing yolk sac placenta. No evidence of the dye in either case could be found in the embryonic tissues proper or within any of the other extraembryonic membranes at any stage of gestation studied. The significance of this apparrent impermeability of the rat placenta to these azoproteins is discussed.