Potential involvement of P2Y2receptor in diuresis of postobstructive uropathy in rats

Abstract

AVP resistance of the medullary collecting duct (mCD) in postobstructive uropathy (POU) has been attributed to increased production of PGE2. P2Y2receptor activation causes production of PGE2by the mCD. We hypothesize that increased P2Y2receptor expression and/or activity may contribute to the diuresis of POU. Sprague-Dawley rats were subjected to bilateral ureteral obstruction for 24 h followed by release (BUO/R, n = 17) or sham operation (SHM/O, n = 15) and euthanized after 1 wk or 12 days. BUO/R rats developed significant polydipsia, polyuria, urinary concentration defect, and increased urinary PGE2and decreased aquaporin-2 protein abundance in the inner medulla compared with SHM/O rats. After BUO/R, the relative mRNA expression of P2Y2and P2Y6receptors was increased by 2.7- and 4.9-fold, respectively, without significant changes in mRNA expression of P2Y1or P2Y4receptor. This was associated with a significant 3.5-fold higher protein abundance of the P2Y2receptor in BUO/R than SHM/O rats. When freshly isolated mCD fractions were challenged with different types of nucleotides (ATPγS, ADP, UTP, or UDP), BUO/R and SHM/O rats responded to only ATPγS and UTP and released PGE2, consistent with involvement of the P2Y2, but not P2Y6, receptor. ATPγS- or UTP-stimulated increases in PGE2were much higher in BUO/R (3.20- and 2.28-fold, respectively, vs. vehicle controls) than SHM/O (1.68- and 1.30-fold, respectively, vs. vehicle controls) rats. In addition, there were significant 2.4- and 2.1-fold increases in relative mRNA expression of prostanoid EP1and EP3receptors, respectively, in the inner medulla of BUO/R vs. SHM/O rats. Taken together, these data suggest that increased production of PGE2by the mCD in POU may be due to increased expression and activity of the P2Y2receptor. Increased mRNA expression of EP1and EP3receptors in POU may also help accentuate PGE2-induced signaling in the mCD.