The Integrative Control of Fluid and Electrolyte Balance in Birds

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9906431BraunIn mammals (humans) the kidney is the only organ that functions to maintain the composition of plasma constant. It is necessary to maintain the composition of the plasma for the cells of the body to function in a normal manner. In birds, the situation with respect to the regulation of the composition of the plasma is slightly different. This is mainly because birds do not have a urinary bladder in which to store urine until it can be conveniently voided and birds excrete nitrogen as uric acid and not as urea as is the case for mammals. Why is this difference between birds and mammals of interest? Several reasons or justifications can be given for gaining a better understanding of kidney function in birds. First, birds (domestic fowl) are of a significant economic importance and second, human health insights can be gained from studies on birds. The research in this proposal is to address how birds regulate their plasma glucose concentration, how birds excrete large amount of nitrogen as uric acid without forming kidney stones, and how birds can conserve body water by producing urine in which the solutes are in a greater concentration than in the plasma. The plasma glucose concentration in humans is normally regulated very closely (normal is 80-100 mg%). If this concentration increases to 120-150 mg% and stays at these levels for a prolonged time, type II contrary, birds (domestic) fowl have plasma glucose concentrations of about 350 mg% as a normal circumstance. Despite these concentrations, they show no symptoms of type II diabetes. A portion of the research on this proposal will be directed toward understanding how birds live with these high plasma glucose concentrations. Answer(s) to this question may help in understanding why humans develop type II diabetes. Birds excrete 75% of their nitrogen as uric acid. Why is this of interest? Uric acid is almost insoluble in water and precipitates from solutions at very low concentrations. If the concentration in human urine exceeds the solubility limits of uric acid, crystals will form. These will lead to kidney stone formation. Birds have very high concentrations of uric acid in their urine, but do not form kidney stones. A portion of the research on this proposal will be directed toward understanding this difference. Birds have much simpler mechanism (but similar to mammals) to concentrate the urine to conserve body water. Because the system is less complicated in birds, it is much easier to study and manipulate. Results from these studies should lead to a better understanding of how the system functions in mammals (humans). Taken as whole, the proposed research should provide better information on kidney function not only in birds, but also in mammals (humans).