Renal cyst epithelial transport in non-uremic polycystic kidney disease

Renal cyst epithelial transport of organic molecules was investigated during three separate cyst drainage procedures in a non-uremic patient with polycystic kidney disease (PCKD). Following constant intravenous insulin infusion, four of eight sampled cysts achieved concentrations exceeding those expected by glomerular filtration alone. Likewise, cyst concentrations of the filtered radionuclide Tc DTPA were up to 3.7 times simultaneous plasma levels. Both PAH and I-131 hippuran accumulated in all cysts suggesting intact tubular secretory mechanisms. Quantitative amino acid levels in two proximal nephron cysts were identical to serum. Since concentrations of inulin, DTPA, and amino acids exceed levels expected if cystic nephrons had normal glomerular filtration and tubular reabsorptive properties, other mechanisms are likely. Simple diffusion across altered epithelial surfaces could partially account for the observed cyst concentrations of each organic molecule and, by ion trapping, contribute to progressive cyst growth in PCKD.