The proposed research is a study of the integrative aspects of fluid and electrolyte balance in birds. Because of the lack of a urinary bladder, the urine of birds enters the terminal portion of the gastrointestinal tract, the cloaca. The urine does not remain here, but moves in an oral direction into the rectum where it comes into contact with epithelial tissues capable of active transport. Thus, conditions are created under which the composition of the urine can be modified. Because of this anatomical and functional relationship, the kidneys of birds do not have sole control of fluid and electrolyte balance, as is the case for mammals. In this proposal, I plan to investigate several components of this system. These are: 1) An investigation of the factors that control the movement of urine from the cloaca into the intestine. Does this movement occur at all times, or does it vary with the composition and volume of the urine? If it does vary, what parameters are sensed and how are they detected? 2) An investigation of the concentrating mechanism of the bird kidney. What limits the capacity of the bird kidney to concentrate the urine? Typically, the kidneys of birds do not concentrate the urine well when compared to those of mammals. 3) An investigation of binding of uric acid to proteins in the urine of birds. The concentration of uric acid in the urine of birds greatly exceeds the solubility limits for this compound. Crystal formation is prevented by the binding of uric acid to a protein (glycoprotein). Where does this protein come from and how does it bind uric acid? Domestic fowl (Gallus domesticus) are to be used as experimental animals to generate data to test the hypothesis of this proposal. Data generated by the proposed research will lead to a better understanding of the regulation of fluid and electrolyte balance and should help to correct some of the misconceptions about avian osmoregulation.//
