Up to 50-fold increase in urine viscosity with iso-osmolar contrast media in the rat.
OBJECTIVE
To compare changes in urinary viscosity in the renal tubules following administration of a high-viscosity iso-osmolar contrast agent (iodixanol) to that observed following administration of a less viscous, higher osmolar contrast agent (iopromide) in anesthetized rats.


METHODS
A total of 43 rats were studied. Experiments were approved by the Berlin, Germany, animal protection administration. A viscometer was developed to measure viscosity in minute samples (7 microL). Urine was collected, viscosity was measured (at 37 degrees C), and glomerular filtration rate (GFR) was determined by means of creatinine clearance. Boluses of 1.5 mL of iodixanol (320 mg iodine per milliliter, iso-osmolar to plasma, high viscosity) or iopromide (370 mg iodine per milliliter, higher osmolality and lower viscosity than iodixanol) were injected into the thoracic aorta. There were five groups (seven rats per group). Groups 1 (iodixanol) and 2 (iopromide) had free access to water prior to the experiment; groups 3 (iodixanol) and 4 (iopromide) received an additional infusion of isotonic saline (4 mL/kg/h). Group 5 was treated as group 1 but received only 0.75 mL of iodixanol. The observation period was 100 minutes. Statistical comparisons were made by means of nonparametric procedures (Friedman test, Kruskal-Wallis test).


RESULTS
Iodixanol increased urine viscosity from 0.69 to 36.7 mm(2)/sec; thus, urine became threefold more viscous than native iodixanol solution. The increase in urine viscosity after injection of iopromide was from 0.73 to 2.3 mm(2)/sec. While GFR was not significantly affected by iopromide, GFR transiently decreased by 50% after administration of iodixanol. Iopromide had a diuretic effect twofold greater than that of iodixanol. Saline infusion blunted the viscosity rise and transient decline in GFR caused by iodixanol, as did reducing the iodixanol dose by 50%.


CONCLUSIONS
Contrast media, in particular iodixanol, increase urine viscosity (which is equal to tubular fluid viscosity in the collecting ducts); in response to iodixanol, GFR markedly decreases. Saline infusion attenuates this response, thus potentially explaining the protective effects of volume expansion in contrast medium-induced nephropathy.
Institute of Vegetative Physiology, Charité-Universitätsmedizin Berlin, CCM, Tucholskystr. 2, D-10117 Berlin, Germany. erdmann.seeliger@charite.de
Erdmann
E
Seeliger
Klaus
K
Becker
Mechthild
M
Ladwig
Thomas
T
Wronski
Pontus B
PB
Persson
Bert
B
Flemming
D000818:Animals; D003287:Contrast Media / Q000008:administration & dosage* / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D014283:Triiodobenzoic Acids / Q000008:administration & dosage / Q000737:chemistry* / Q000652:urine*; D014556:Urine / Q000737:chemistry*; D014783:Viscosity
D003287:Contrast Media; D014283:Triiodobenzoic Acids; C044834:iodixanol