Roentgen-ray Study on Non-permeability to Thorium Dioxide of Placenta of Albino Rat. ∗

Abstract

Experimental work on the permeability of the placenta to certain dyestuffs has been reported by a number of investigators. Wislocki 1 reports that when phenolsulphonephthalein is injected into the peritoneal cavity of a guinea pig fetus it is absorbed and passes slowly from the fetal blood stream through the placenta into the maternal blood stream and is excreted by the maternal kidney. A similar injection of trypan blue is also absorbed from the peritoneal cavity of the fetus, but is not transmitted by the placenta to the maternal organism. According to Wislocki's observations the placenta is incapable of transmitting an inert foreign colloid from the fetus to the mother. Shimidzu 2 injected pregnant rats subcutaneously between the scapulae, using 23 different dyes, 8 basic and 15 acidic. He found that the placenta was permeable to all of the basic dyes, and only 8 out of the 15 acid dyes penetrated the placenta; also that the permeable dye solutions were slightly colloidal or non-colloidal in character, with the exception of Biebrich's scarlet, a highly colloidal dye. Dyes largely in the colloidal state do not, with rare exceptions, penetrate the placenta. These experiments were made on animals either at operation or after death.

We were unable to find in the literature reports of experiments on the permeability of the placenta to colloidal substances opaque to the roentgen ray. We appreciated that but few colloidal substances have been found which penetrate the placenta because of the size of the particles in these substances. We used thorotrast, a colloidal thorium dioxide, miscible in all proportions with body fluids. We hoped that its particles of thorium would be small enough to penetrate the placenta, as in the instance of Biebrich's scarlet, and thereby visualize the reticulo-endothelial system of the fetus.