RBP EXCRETION

Excretion of RBP in the kidneys with A vitamin deficiency.

Original source: Charles B Stephensen: VITAMIN A, INFECTION, AND IMMUNE FUNCTION Annu. Rev. Nutr. 2001. 21:167–92

Figure Mechanism of urinary retinol excretion during infection. Retinol, bound to retinol-binding protein (RBP), is normally retained in the glomerular capillaries by its association with transthyretin (TTR). If not bound to TTR, RBP is small enough to pass through the fenestrations of the glomerular capillaries into the urinary collecting tubules, which begin with Bowman's capsule. Under normal circumstances, RBP passes down the tubules but is reabsorbed by the proximal tubular epithelial cells. During infections, particularly those with high fever, this reabsorption is diminished and RBP, carrying retinol, is lost in the urine.