Uric Acid Excretion in the Chick as Related to the Intake of Its Precursors and Nitrogen

URIC acid is the main end product of nitrogen metabolism in the bird. This phenomenon appears to have arisen evolutionwise because of the limited availability of water to the developing embryo. Uric acid is relatively non-toxic, and highly insoluble; thus, it can be excreted into the allantois of the embryo without causing toxemia or dehydrating the embryo because of the high osmotic pressure a more soluble material would create (Baldwin, 1957). Sixty to eighty percent of urinary nitrogen of chickens is found in uric acid (Milroy, 1904; Paton, 1905; and Davis, 1927). Recent isotopic work (Barnes and Schoenheimer, 1943; Sonne et al., 1946; Buchanan and Sonne, 1946; Sonne et al., 1948; Buchanan et al., 1948) has shown the precursors of uric acid to be carbon dioxide, formate, glycine in toto and nitrogen from the general pool. The methyl group of methionine has also been reported to be a source of …