Chemical nature of some substances required for the growth of fibroblasts and epithelial cells.

Abstract

Pure strains of fibroblasts or of epithelial cells increase in mass in an unlimited manner, when they are cultivated in plasma and embryonic tissue juice. For 14 years, colonies of a strain of fibroblasts have doubled in size every 48 hours in such a medium. Pavement and thyroid epithelium also have been found to manufacture unlimited amounts of protoplasm from the constituents of embryonic juice. Neither epithelial cells nor fibroblasts multiply in serum proteins, egg albumin, crystallized egg albumin, amino acids from embryonic juice, or artificial mxtures of amino acids for a longer time than in Tyrode solution. So far, embryonic juice is the only material which has been found to maintain epithelial cells and fibroblasts in a conditoti of true cultivation.

Investigation of the chemical nature of the nutritive materials in the embryo juice has led to the conclusion that the nitrogenous substance utilized by the tissues is the protein itself. The amino acids and other ultra-filtrable and dialyzable constituents slightly stimulated the migration and multiplication of the cells, but failed to produce an increase in the mass of the tissues. Since the protein of the embryo juice is utilized by the cells, it seems evident that it must be hydrolyzed and some intermediate product absorbed. Complete digestion by trypsin and pepsin produced only toxic substances.

However, some of the higher cleavage products formed by the partial hydrolysis of protein have been found to produce the same effect as the protein of the embryo juice, causing continuous multiplication of cells and increase in the mass of tissue for long periods of time. In fact, some preparations of these protein hydrolytic products have given a larger increase in the mass of the tissue than has ever been obtained by embryo juice.