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Plasma arginine vasotocin and angiotensin II concentrations during saline acclimation in birds with salt glands Zenteno Savin, Tania


Pekin ducks (Anas platyrhynchos), Canada geese (Branta canadensis) and Glaucous-winged gulls (Larus glaucescens) responded differently during acclimation to saline equivalent to full strength sea water. All species were in hydrosmotic balance until they were given 375 mM NaCl. When the birds drank 75 mM NaCl ducks transiently decreased plasma sodium concentration ([Na⁺][formula omitted]) and osmolality (Osm[formula omitted]) and increased cloacal Na⁺ excretion; geese transiently increased hematocrit (Hct), suggesting transient extracellular dehydration; and gulls increased Osm[formula omitted] (but not Hct), suggesting that their Osm[formula omitted] had been below normal when fresh water was offered. During acclimation to moderately concentrated saline, all species progressively increased plasma arginine vasotocin levels ([AVT][formula omitted]) (without concomitant increase in Osm[formula omitted]) and decreased plasma angiotensin II concentration ([Ang II][formula omitted]) without parallel changes in Hct. Following acclimation to 300 mM NaCl total body water (TBW) was increased in ducks and geese, but acclimation to 375 mM NaCl did not affect TBW in gulls. When they drank 450 mM NaCl, ducks and geese decreased body mass and increased Hct, plasma electrolyte and osmotic concentrations, [AVT][formula omitted] and [Ang II][formula omitted], indicating they were dehydrated. In contrast, saline acclimated gulls did not increase [Ang II][formula omitted] and increased [AVT][formula omitted] less than ducks or geese. Initial [AVT][formula omitted] was not significantly correlated with sex in either ducks or geese. Female ducks increased [Ang II[formula omitted] and Osm[formula omitted] less than males during exposure to 450 mM NaCl, while female geese increased [Ang II][formula omitted] more than males. Salt gland NaCl secretion and renal water retention counterbalanced NaCl ingested in low to moderately concentrated saline in ducks, geese and gulls, but not in ducks and geese drinking saline equivalent to sea water. Gulls likely maintained simultaneous, concerted function of kidneys and salt glands during high salt intake, while cloacal excretion may have decreased in the Anatidae. Based on their relative salt secreting efficiencies, plasma ionic concentrations, Osm[formula omitted] and Hct increased much more in ducks than in geese when they drank 450 mM NaCl, and remained unchanged in gulls drinking 375 mM NaCl. Release of AVT and Ang II in birds with salt glands appears to be controlled by a complicated interrelationship between volume and tonicity (threshold for release varies among species), and these (and possibly other) hormones may affect salt gland and kidney function to maintain salt and water balance.

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