Inhibition of prostaglandin biosynthesis in renal (MDCK) cells by cAMP

Cultured renal tubular cells (MDCK) have many of the biological properties of renal medullary tubular epithelial cells, including the ability to synthesize prostaglandin E2 (PGE2) as the major arachidonate metabolite. The hypothesis that adenosine 3',5'-cyclic monophosphate (cAMP) regulates prostaglandin synthesis in these cells was investigated by using cAMP, two degradation-resistant cAMP analogues [8-bromo-cAMP (8-BrcAMP) and N6,O2'-dibutyryl cAMP (DBcAMP)], and a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). These agents inhibited basal-, calcium ionophore (A23187)-, or bradykinin-stimulated PGE2 biosynthesis by MDCK cells. The observed inhibition was dose- and time-dependent and could be reversed after 30 min of incubation in the absence of inhibitor. IBMX dose-dependently increased intracellular and extracellular cAMP levels by severalfold, suggesting that it was inhibiting prostaglandin biosynthesis by increasing cellular cAMP levels. Vasopressin, which stimulated cAMP levels by less than two-fold, did not inhibit prostaglandin synthesis. 8-BrcAMP and N6,O2'-DBcAMP inhibited A23187- or bradykinin-stimulated release of [3H]arachidonate from prelabeled cells, suggesting that cAMP inhibited acylhydrolase activity. Moreover, 8-BrcAMP also inhibited the conversion of exogenous arachidonate to PGE2 in intact cells and in a subcellular fraction containing prostaglandin synthetase activity, suggesting that cAMP inhibited cyclooxygenase and/or PGE2 isomerase activity. cAMP thus appears to regulate prostaglandin biosynthesis in MDCK cells by modulating the activity of two or more of the enzymes involved in the biosynthetic process.