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Uric acid decomposition in the lower gastrointestinal tract.
1Department of Physiology, College of Medicine, University of Arizona, Tucson.
The Journal of Experimental Zoology. Supplement : Published Under Auspices of the American Society of Zoologists and the Division of Comparative Physiology and Biochemistry
|January 1, 1989
Summary
Birds reclaim nutrients from urine using a unique uric acid-to-VFA pathway. Bacterial degradation of uric acid spheres in the ceca recovers carbon and nitrogen, preventing waste.
Area of Science:
- Avian physiology
- Microbiology
- Biochemistry
Background:
- Uric acid, the end product of nitrogen metabolism in birds, has very low aqueous solubility.
- Despite low solubility, uric acid crystals are rarely found in bird urine; instead, it is packaged into spheres.
- These spheres navigate the renal duct system and are transported to the cloaca and digestive ceca.
Purpose of the Study:
- To investigate the fate and metabolic significance of uric acid spheres in avian urinary and digestive systems.
- To elucidate the role of cecal bacteria in uric acid degradation and nutrient reclamation.
Main Methods:
- Observation of uric acid sphere transport through the avian renal and cloacal systems.
- Analysis of the microbial population and metabolic activity within the digestive ceca.
- Identification of metabolic products derived from uric acid degradation.
Main Results:
- Uric acid spheres are efficiently transported from the kidney to the ceca via antiperistalsis.
- Cecal bacteria metabolize uric acid into volatile fatty acids (VFA) and ammonia.
- Absorbed VFA provide energy to cecal tissue, and ammonia is used for glutamine synthesis.
Conclusions:
- The reflux of uric acid into the ceca facilitates its bacterial degradation.
- This process represents an effective mechanism for avian nutrient reclamation, recovering carbon and nitrogen from urine.
- The avian urinary-digestive tract synergy optimizes resource utilization.