RESPONSES OF GULL KIDNEYS AND SALT-GLANDS TO NACL LOADING

Glomerular filtration rate was measured in Glaucous-winged Gulls, Laru s glaucescens, acclimated to freshwater or saline and was also measure d (along with salt gland secretion) following intravenous and intragas tric 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 +/- 2 0 and 46 +/- 19 mu L . min(-1) . kg(-1); urine/plasma osmolality ratio , 1.2 +/- 0.2 and 1.7 +/- 0.1; urine/plasma [C-14]polyethylene glycol ratio, 210 +/- 69 and 211 +/- 64; and Na+ reabsorption, 99.6 +/- 0.2 a nd 99.6 +/- 0.3%, respectively. Renal function during 143 mM NaCl infu sion (glomerular filtration rate, 3.4 +/- 0.3 mL . min(-1) . kg(-1); u rine flow rate, 19.7 +/- 2.8 mu L . min(-1) . kg(-1); urine/plasma osm olality ratio, 1.7 +/- 0.1; urine/plasma [C-14]polyethylene glycol rat io, 223 +/- 26, and Na+ reabsorption 99.9 +/- 0.0%) was not affected b y subsequent infusion of 700 mM NaCl, although plasma osmolality was s ignificantly increased. The urine/plasma ratio for [C-14]polyethylene glycol, but not osmolality, was higher in gulls than in other avian sp ecies. Intravenously infused NaCl elicited less concentrated salt glan d secretion at a significantly lower threshold plasma osmolality than intragastric NaCl infusion. Salt gland secretion and glomerular filtra tion rates were inversely related.