Elevation of plasma retinol binding protein concentration in experimental acute renal failure

Abstract

The effect of acute renal failure on plasma retinol, retinol binding protein(RBP) concentrations and liver RBPmRNA were examined to clarify the role of kidney in vitamin A homeostasis. Male Sprague-Dawley rats fed a sufficient vitamin A containing diet(AIN-76 composition) for 2 weeks were bilaterally nephrectomized or sham-operated. Blood samples from the heart and the liver were collected (6animals/group) at 0,3,12 and 24 hours after surgery. The amounts of retinol and retinol binding protein(RBP) were determined in the plasma using reversal phase HPLC or a monospecific antiserum by ELISA method, respectively. As early as 3 hours after nephrectomy, plasma retinol levels increased 1.5fold compared to sham-operated controls. This elevated level was maintained for 24 hours. RBP level(Mean±SE) in the plasma showed 26±5, 44±3, 55±6, 54±7 μg/ml after 0, 3, 12, 24 hours, respectively. RBP concentration had a close correlation with retinol in the plasma(R=0.83). On the other hand, retinol, retinyl ester and RBP concentrations in the liver did not change. The liver RBPmRNA abundance were kept essentially the same level in sham-operated and in nephrectomized rats. Size-exclusion HPLC using TSK G-2000sw column and fluorescence/ELISA detection revealed that the increased RBP in plasma was mainly RBP-transthyretin complex. There was a slight increase in the elution area of retinol-RBP of only nephrectomized rats at 24 h after surgery. These results suggest that the releases of retinol and RBP from the liver might not directly be related to the elevated plasma vitamin A homeostasis in the acute renal failure.