The effects of ureteral resistance on gull urine composition and flow rate

Abstract

The effects of ureteral resistance on the ionic and osmotic composition of urine were examined in five anesthetized Glaucous-winged Gulls, Larus glaucescens, orally loaded with 0.075 M NaCl. One ureter was cut caudad to the kidney and the cloaca was opened to expose the contralateral ureteral papilla. The [Na] of urine leaving the kidney (renal urine) was less than plasma [Na] and positively correlated with flow rate. Renal urine [Cl] was less than plasma [Cl] at flow rates less than 50 μL min−1, but higher than plasma [Cl] at greater flow rates and was positively correlated with flow rate. Renal urine [K] was greater than plasma [K] at all flow rates, but markedly so below 20 μL min−1. Ureteral transit did not affect ion concentrations, but decreased (P < 0.01) urine volume and increased (P < 0.001) osmotic concentration, suggesting that the rapid flow of fluid through the renal tubules reduced isosmotic NaCl uptake and addition of osmotically active substances. Glomerular filtration was determined by inulin clearance rate in four anesthetized gulls as 4.88 ± 0.27 mL min−1 kg−1. The percentage of filtered Na, Cl, and water reaching the ureters was 0.83, 1.04, and 1.76, respectively. The ureter may influence the ureteral urine composition by regulating the rate of passage of urine through the kidney.