Cyst fluids from subjects with autosomal dominant polycystic kidney disease (ADPKD) cause polarized monolayers of MDCK cells to secrete fluid toward the apical compartment in vitro. To determine the extent to which secretagogue accumulation may be a general feature of polycystic diseases, cyst fluid from mice with a slowly progressive form of hereditary PKD (DBA/2FG-pcy/pcy) was added to polarized MDCK monolayers. Basolateral application of cyst fluids (diluted with culture medium to 15% final concentration) from 13 different animals 16 to 35 weeks old increased the fluid secretion rate from a baseline of 0.023 ± 0.003 to 0.111 ± 0.017 μL/cm2/h (P < 0.005). There was a direct relation between the concentration of cyst fluid and the rate of net fluid secretion. The secretory activity of cyst fluid was not altered by pronase treatment or boiling. Cyst fluid (10%) added to the basolateral surfaces of polarized MDCK monolayers for 24 hours increased cell cyclic adenosine monophosphate (AMP) levels from a baseline of 6.3 ± 0.2 to 17.3 ± 0.3 pmoles/monolayer (n = 3, P < 0.05). The capacity of cyst fluid to increase cyclic AMP levels was not changed by pronase treatment or boiling. There was a direct relation between the level of cellular cyclic AMP and the rate of transepithelial fluid secretion caused by cyst fluid. Cyst fluid increased thymidine incorporation by Madin-Darby canine kidney (MDCK) cells to an extent equal to that caused by epidermal growth factor and caused MDCK cells to form cysts in collagen matricies. The mitogenic activity of cyst fluid was decreased 62% by pronase treatment, suggesting that the substance(s) responsible for the mitogenic activity may not be the same as that causing fluid secretion. On the basis of these studies, the authors conclude that, like human ADPKD, fluids in the cysts of a slowly progressive murine model of PKD contain material capable of stimulating fluid secretion and mitogenesis in MDCK cells in vitro. The cyclic AMP signal pathway appears to have an important role in mediating the intracellular actions of endogenous factors that have the capacity to stimulate cyst growth.
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