The Patterns of Renal Electrolyte Excretion in the Duck (Anas platyrhynchos) Maintained on Freshwater and on Hypertonic Saline*

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Abstract
1. The renal excretion of water and electrolytes was examined in starved ducks maintained on fresh water and on hypertonic saline containing 284 mM/1. NaCl and 6.0 mM/l. KCl. 2. No significant differences were observed in the urine flow, glomerular filtration rate, renal plasma flow and the excretory rates of K+, NH4+ and inorganic phosphate between these two groups of birds. 3. The excretory rates of Na+, Cl- and Ca2+ were significantly higher in saline-maintained birds than in the freshwater-maintained birds. 4. NH4+ appeared to be a major cationic component which occupied over half of the available osmotic space in the urine of both the freshwater-maintained and saline-maintained birds. 5. In saline-maintained birds the excretion of K+ and inorganic phosphate appeared to be independent of the available osmotic space in the urine whereas the excretion of Na+ and Cl- appeared to be very dependent upon this factor. 6. These observations suggest that the kidneys of the saline-maintained bird constitute the primary pathway for the excretion of K+, NH4+ and inorganic phosphate, and that with respect to the excretion of Na+ they constitute a relatively minor pathway.