Osmoregulatory responses of glaucous-winged gulls (Larus glaucescens) to dehydration and hemorrhage

The effects of dehydration and hemorrhage on plasma ionic, osmotic, and antidiuretic hormone (arginine vasotocin) concentrations and of hemorrhage on salt gland secretion and glomerular filtration rate were evaluated in glaucous-winged gulls, Larus glaucescens. Dehydration for 24 h did not affect plasma ionic, osmotic or arginine vasotocin concentrations; 72 h dehydration significantly elevated plasma osmolality, plasma sodium and chloride concentrations, and plasma arginine vasotocin concentration, but did not affect plasma potassium concentration. Constant infusion of 0.8 mol·l^-1 NaCl increased plasma arginine vasotocin concentration and produced salt gland secretion in seven gulls; four secreted well, while three secreted less well. Removal of 20% blood volume during saline infusion immediately reduced (P<0.001) salt gland secretion rate in all gulls. After bleeding, good secretors maintained glomerular filtration rate and urine flow rate; the poorer secretors increased glomerular filtration rate and became diuretic. Blood replacement returned salt gland secretion rate to the prebleeding level (P<0.05) without affecting salt gland secretions sodium concentration in gulls which secreted well, but did not restimulate salt gland secretion in gulls which secreted poorly. Reinfusion of blood had no effect on glomerular filtration rate. Bleeding and blood replacement did not affect plasma arginine vasotocin concentration.Abbreviations AVT arginine vasotocin - ECF extracellular fluid - ECFV extracellular fluid volume - EDTA ethylenediaminetetra-acetate - EWL evaporative water loss - GFR glomerular filtration rate - Hct hematocrit - LB large blood sample - [Na⁺]_pl plasma sodium concentration - Osm_pl plasma osmolality - PEG polyethylene glycol - RH relative humidity - RIA radioimmunoassay - SB small blood sample - SGS salt gland secretion - T_a ambient temperature - TFA trifluoroacetic acid - UFR urine flow rate