2 MECHANISMS OF INHIBITION BY PROSTAGLANDIN-E2 OF HORMONE-DEPENDENT CELL CAMP IN THE RAT COLLECTING TUBULE

The effect of exogenous prostaglandin E2 (PGE2) on hormone-dependent adenosine 3',5'-cyclic monophosphate (cAMP) accumulation was investigated by microradioimmunoassay in collecting tubules microdissected from the cortex (CCT) or outer medulla (MCT) of the rat kidney. Two phosphodiesterase inhibitors were used: either a xanthine derivative (isobutyl-methylxanthine (IBMX, 1 mM)) active on all forms of phosphodiesterase or Ro 20-1724 (50 μM) active on the phosphodiesterase type III. A prostaglandin synthesis inhibitor was added to all media. In the presence of IBMX, 0.3 μM PGE2 inhibited by 39.1% the response induced in the CCT by the β-adrenergic agonist isoproterenol (1 μM). Under the same experimental conditions, arginine vasopressin (AVP)-stimulated cAMP accumulation in CCT or MCT was not affected by PGE2. In the presence of Ro 20f-1724, 0.3 μM PGE2 did not modify the response to 1 nM AVP in CCT but inhibited this response in MCT samples (mean inhibition: 52.7%). The inhibition by PGE2 was dose dependent with a maximum at 0.3 μM, observed for all concentrations of AVP tested (from 50 pM to 1 nM) and did not affect the concentration of AVP inducing half-maximal cAMP accumulation. In a second experimental series performed in the presence of adenosine deaminase, an A1adenosine agonist ((θ)-N6-(R-phenylisopropyl)adenosine (PIA, 0.1 μM)) also decreased the response to 1 nM AVP in the MCT. The addition of an A1-adenosine antagonist relieved the effect of PIA but did not modify the inhibition observed with PGE2. Thus PGE2 decreased the synthesis of cAMP in β-adrenergic sensitive cells in rat CCT and might affect the catabolism of AVP-dependent cAMP level rather than its synthesis in rat MCT. © 1990.