EFFECTS OF CECAL LIGATION AND SALINE ACCLIMATION ON PLASMA-CONCENTRATION AND ORGAN MASS IN MALE AND FEMALE PEKIN DUCKS, ANAS-PLATYRHYNCHOS

The intestinal caeca reabsorb urinary sodium chloride (NaCl) and water (Rice and Skadhauge 1982). Free water may be generated if the reabsorbed NaCl is secreted via salt gland secretion (Schmidt-Nielsen et al. 1958). Therefore ceacal ligation should (a) reduce hind-gut NaCl and water reabsorption, (b) enhance the increase in plasma osmolality during saline acclimation, and (c) affect drakes more than ducks. Twelve Pekin drakes and 13 Pekin ducks, Anas platyrhynchos, were caecally ligated or sham operated before acclimation to 450 mmol . l NaCl. Body mass, hematocrit, plasma osmolality, and ionic concentrations of plasma, cloacal fluid, and salt gland secretion were measured after each increase in drinking water salinity. Osmoregulatory organ masses were determined. Caecal ligation did not affect plasma osmolality or ion concentrations of plasma, cloacal fluid, or salt gland secretion, but reduced salt gland size in ducks. Drakes and ducks drinking fresh water had the same hematocrit, plasma osmolality, and plasma concentrations of Na+ and Cl-. In both sexes exposure to 75 mmol . l-1 NaCl significantly decreased plasma [Na+] and doubled cloacal fluid [Na+]. Exposure to 450 mmol - l-1 NaCl decreased body mass and increased hematocrit, plasma [Na+], [CI-], and plasma osmolality (more in drakes than in ducks); cloacal fluid osmolality nearly doubled compared to freshwater-adapted ducks, due mainly to osmolytes other than Na+ and Cl-. The [Cl-] in salt gland secretion only slightly exceeded drinking water [CI-].