The Renal Excretion of Nitrogenous Compounds by the Duck (Anas Platyrhynchos) Maintained on Freshwater and on Hypertonic Saline

Abstract

1. The excretory rates of total nitrogen, uric acid, urea and ammonia by intact birds maintained on fresh water did not differ significantly from the corresponding rates of excretion by birds maintained on saline equivalent to 60% sea water (284 mM-NaCl, 6.0 mM-KCl). 2. The uric acid excreted by these birds contributed 53.8%, the ammonia 29.2% and the urea 1.5% of the total nitrogen excreted. The three compounds together accounted for 84.5% of the nitrogen excreted. 3. The glomerular filtration rates (inulin clearance) and the renal plasma flow rates (PAH clearance) did not differ between the freshwater-maintained and the salinemaintained birds. 4. The clearance of uric acid in all groups of birds was equal to the PAH clearance and may be interpreted as a reliable measure of the renal plasma flow rate. 5. The urea:inulin clearance ratios for the individual urine samples from all birds suggested that renal tubular synthesis and secretion of urea may occur. 6. In a second set of experiments uric acid and urea concentrations in the plasma of fed ducks were followed during adaptation to hypertonic saline and during a similar period of dehydration. 7. A sharp in the increase plasma uric acid concentration was generally observed in all groups of birds after feeding and the concentration then gradually declined to the prefeeding level. 8. The plasma urea concentrations of birds given saline equivalent to 60% sea water equilibrated, after the first 24 hr., at about twice the concentration found in the freshwater-maintained birds. 9. In birds maintained on saline equivalent to 100% sea water (470 mM-NaCl; 10 mM-KCl), the plasma urea concentration steadily rose during the first 50 hours and then equilibrated at a level approximately 10 times that observed in freshwatermaintained birds. 10. Withholding all drinking water from birds which had been previously given fresh water resulted in a rise in the plasma urea concentration during the first 50 hr. similar to that observed in the birds maintained on saline equivalent to 100% sea water. But the plasma urea concentration of these birds, in contrast to that of salinemaintained birds, continued to rise throughout the remainder of the experimental period.