A new method for collecting urine directly from the ureter in conscious unrestrained rats

We have developed a new method for urine collection in conscious, unrestrained rats through a chronic indwelling ureteral catheter, which allows direct differential sampling of small urine fractions over periods as small as 1 min. The technique was validated in intact and unilaterally nephrectomized rats by cumulative intravenous saline loading. Comparison of kidney with ureter catheter and contralateral kidney (urine collection from the bladder) revealed no differences in glomerular filtration rate and urine production between both kidneys. One week after catheter implantation in unilaterally nephrectomized rats, signs of renal functional disturbance as assessed by glomerular filtration rate, urine concentrating capacity after 24 h water deprivation, and plasma and urinary urea concentrations before and after water deprivation were not detected. Our technique provides a novel tool for direct measurements of short-term changes in urine composition in conscious animals.