Responses of gull kidneys and salt glands to NaCl loading

Abstract

Glomerular filtration rate was measured in Glaucous-winged Gulls, Larus glaucescens, acclimated to freshwater or saline and was also measured (along with salt gland secretion) following intravenous and intragastric infusion of 700 mM sodium chloride (NaCl). Freshwater- and saline-acclimated gulls had the same mean glomerular filtration rate, 5.6 ± 0.8 and 6.1 ± 1.0 mL ∙ min⁻¹ ∙ kg⁻¹; urine flow rate, 44 ± 20 and 46 ± 19 μL ∙ min⁻¹ ∙ kg⁻¹; urine/plasma osmolality ratio, 1.2 ± 0.2 and 1.7 ± 0.1; urine/plasma [¹⁴C]polyethylene glycol ratio, 210 ± 69 and 211 ± 64; and Na⁺reabsorption, 99.6 ± 0.2 and 99.6 ± 0.3%, respectively. Renal function during 143 mM NaCl infusion (glomerular filtration rate, 3.4 ± 0.3 mL ∙ min⁻¹ ∙ kg⁻¹; urine flow rate, 19.7 ± 2.8 μL ∙ min⁻¹ ∙ kg⁻¹; urine/plasma osmolality ratio, 1.7 ± 0.1; urine/plasma [¹⁴C]polyethylene glycol ratio, 223 ± 26, and Na⁺reabsorption 99.9 ± 0.0%) was not affected by subsequent infusion of 700 mM NaCl, although plasma osmolality was significantly increased. The urine/plasma ratio for [¹⁴C]polyethylene glycol, but not osmolality, was higher in gulls than in other avian species. Intravenously infused NaCl elicited less concentrated salt gland secretion at a significantly lower threshold plasma osmolality than intragastric NaCl infusion. Salt gland secretion and glomerular filtration rates were inversely related.Key words: bird, gull, Larus glaucescens, kidneys, salt glands, gut, sodium chloride, glomerular filtration rate, saline acclimation.