Effects of water load on renal glomerular and tubular function in desert quail

Effects of an acute intravenous water load on glomerular and tubular function were studied in the anesthetized desert quail Lophortyx gambelii. Total-kidney glomerular filtration rate (GFR) and single-nephron glomerular filtration rates (SNGFR) of reptilian-type and mammalian-type nephrons increased by more than 50% compared with the GFR and SNGFRs measured during a control mannitol diuresis. Despite the increase in GFR, urine flow rate was only 56% of that in control mannitol diuresis, free-water clearance (CH2o) remained at 1-2% of GFR, and the animals excreted only about 79% of the water load. More than 99% of the filtered sodium and 93% of the filtered water were reabsorbed during the water load. Possible reasons for the increased GFR and the failure to produce a dilute urine or excrete the water load are discussed.