Intersexual Comparison of Plasma Osmolytes, Kidney Size, and Glomerular Number and Size in Pekin Ducks (arias Platyrhynchos)

Increased sodium chloride (NaC1) intake resulted in sexually disparate changes in body mass and plasma osmolality (Osmp•; Hughes et al. 1992) and plasma concentrations of the osmoregulatory hormones arginine vasotocin ([AVT]p 0 and angiotensin II ([AII]p•; Zenteno-Savin 1991) in Pekin ducks (Anas platyrhynchos).During gradual increase in drinking water NaC1 concentration ([NaC1]), both sexes maintained body mass and changed Osmp•, [AVT]p•, and [AII]p• similarly until they drank 300 mM NaC1; at higher [NaC1], males became more dehydrated and their Osm•, [AVT] p•, and [AII]• increased significantly more than in females.Kidney mass tended to be smaller in male ducks than in female ducks (Hughes et al. 1989(Hughes et al. , 1992)).In this study, we reexamined body mass, hematocrit (Hct), plasma ion concentrations, and Osmp• of male and female Pekin ducks rapidly acclimated (over three weeks) to 225 mM NaC1 and following longer exposure to this [NaC1] (four and seven months).Finally, the ducks were euthanized and dissected to obtain organ masses.We found female ducks had larger kidneys, so we counted glomeruli (nephrons) in kidneys of both sexes to determine if the kidneys of females actually contained more nephrons.We also measured glomerular diameters to determine if glomerular sizes were equally represented in both sexes.Methods and materials.--TwelvePekin ducks (6 male, 6 female) were reared for six months in adjacent enclosures on ad libitum tap water and duck pellets (Buckerfield's, Abbottsford, British Columbia; sodium, [Na-•], potassium, [K-•], and chloride, [C1-], concentrations, 83, 153.5, and 99 mM.Kg -•, respectively).They were then acclimated in three equal weekly increments to 225 mM NaC1.Drinking this solution at the minimum rate measured for Pekin ducks (Hughes et al. 1991) should replace at least one-half of the Na* in the extracellular fluid each day.This Na -• intake should have been sufficient to increase the secretory potential of the salt glands allowing Osmp• to be maintained (Hughes et aL 1992).At the end of each week, birds were weighed and 5.0 mL blood samples were taken.The birds were held on 225 mM NaC1 for seven months and blood samples were taken at the end of the fourth and seventh months.Triplicate Strumia microhematocrit tubes were immediately filled from each blood sample and centrifuged simultaneously with the remaining blood for 3 min at 15,600 x g.After the last blood sampling, four female and three male ducks were intravenously infused with Alcian blue for 30 min to stain the glomeruli (Bankir and Hollenberg 1983) and then euthanized with a lethal dose of sodium pentobarbitol.The heart, liver, kidneys, and salt, adrenal, and Harderjan glands were removed and weighed with a Mettier top-loading balance with an accuracy of 1 mg.Experiments conformed to guidelines of the Canadian Council on Animal Care.All analyses were done at least in duplicate.De-782 Short Communications and Commentaries [Auk, Vol.112 lustrated by their diet during spring migration.Ornis Scan& 9:178-192.

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