The Integrative Aspects of Fluid and Electrolyte Balance in Birds

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The proposed research is to study how two organ systems are integrated to regulate fluid and electrolytes in birds. In mammals the output of the kidneys (the urine) is conveyed to a storage organ, the urinary bladders. This urine, once it leaves the kidneys is not modified. Birds do not have urinary bladders to store the urine. Instead the urine is conveyed by the ureters to the terminal segment of the gastrointestinal tract (the cloaca). The urine does not remain here. It is carried into the colon by a reverse action of the colonic muscle layers. In the colon, the urine formed by the kidneys can be modified. How the kidneys and colon of birds are integrated into a unit that functions in a concerted fashion to maintain the fluid and electrolyte balance is not understood. The research outlined in this proposal is directed toward answering some aspects of this basic question. A second aspect of the proposal deals with the chemistry of nitrogen excretion in birds. Mammals (including humans) excrete the majority of waste nitrogen as urea, a very water soluble compound. Birds excrete waste nitrogen in the form of uric acid, a very water insoluble compound. Excreting nitrogen as uric acid could lead to problems of kidney stone formation as it does in humans. However, birds excrete large amounts of uric acid without forming kidney stones. How this occurs is not understood. A portion of this grant proposal deals with research that is directed toward answering this very fundamental question.