Bilirubin nephropathy in the Gunn strain of rat

Abstract

Homozygous, jaundiced, Gunn rats were compared with heterozygous control animals for their capacity to concentrate their urine after water deprivation. During the last 6 hr of a 28-hr period of thirsting and fasting, the mean urinary flow rates were 50 and 149 [mu]l/100 g per hr for the heterozygous and homozygous animals, respectively. The corresponding urinary osmolalities were 1,909 and 815 milliosmols/kg H2O. Both groups of animals excreted comparable total solute loads, but the homozygous animals had a 30% greater loss in total body weight. The urinary sodium losses in the jaundiced rats were three times greater than was found for the control animals. Analysis of the medullary solute composition demonstrated that the concentration gradient for sodium between the cortex and papilla in the homozygous rat was only 30 mEq/liter tissue water. Regional analysis of the kidneys for bilirubin demonstrated a 100-fold greater concentration of bilirubin in the renal papilla than in the corresponding cortex. These results were interpreted to suggest that bilirubin in high concentrations may interfere with sodium re-absorption from the tubular fluid within the ascending limb of the loop of Henle in the kidney.