The metabolism of carbon-labeled urea in the germ free rat.

For many years, urea was considered an end product of amino acid metabolism in mammals. With the advent of isotopic techniques (l-3), it was realized that further catabolism of urea occurred, probably due to bacterial action in the gut. Dintzis and Hastings (4) found that by feeding a mixture of various antibiotics to mice, the breakdown of urea to carbon dioxide and ammonia was almost completely abolished. From this, they concluded that enzymatic hydrolysis of urea in mammals is effected only by urease of the bacteria present in the gut. Kornberg et al. (5, 6) also arrived at this conclusion from their experiments in cats. We have subjected this thesis to direct test in the “germfree” animal.