Ureotelic metabolism

Birds and reptiles are oviparous, and the cleidoic eggs that they produce contain all the nutrient required until hatching. This nutrient, which is mainly protein and lipoprotein, is synthesised in the liver and oviduct prior to oviposition. Lipoproteins are discussed in Section 4.5, and the control of egg protein synthesis in Section 10.3. Birds excrete a semi-solid urine, and this requires a lower water intake than is possible in ureotelic animals. The metabolic adaption that allows this to occur is the excretion of nitrogen principally in the form of uric acid. Uric acid is sparingly soluble in water and is present in avian ureters largely as a colloidal suspension. This is discussed in Section 5.4. 

Most of the animals listed in Table lO-I are ureotelic or ammoniotelic i.e., urea or ammonia is the chief end product of protein metabolism. Birds,... 

Studies of the regulation of glutamine metabolism in birds (urecotelic) and mammals (ureotelic) may be relevant to the pathogenesis of gout. The major func-... 

The end products of purine metabolism are uric acid in primates and uricotelic animals, allantoin in mammals other than primates, urea in the rest of the ureotelic animals, and ammonia in many of the ammonotelic animals. 

This species difference may be associated with the fact that birds and mammals differ profoundly in their nitrogenous metabolism the bird being uricotelic, arid excreting waste protein nitrogen as uric acid, whereas the mammal is ureotelic, and excretes nitrogen chiefly as urea (p. 378). 

Transformation and Degradation of Purine in Animals.—Animals other than birds and reptiles excrete their waste protein nitrogen in the urine, and are said to be ureotelic. In ureotelic animals, purine metabolism proceeds along independent lines. The purines of the diet, chiefly nucleotides and nucleosides liberated from nucleo-proteins, are resolved into their constituent amino purines by the enzymes of the alimentary tract and mucosa. The amino purines are absorbed into the portal s3rstem, and if not utilised, are de-aminated by the appropriate enzjones, adenase and guanase, found in the liver. 

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