Two mechanisms of inhibition by prostaglandin E 2 of hormone-dependent cell cAMP in the rat collecting tubule

Abstract

The effect of exogenous prostaglandin E 2 (PGE 2) 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 PGE 2 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 PGE 2. In the presence of Ro 20f-1724, 0.3 μM PGE 2 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 PGE 2 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 A 1adenosine agonist (( θ)- N 6-( R-phenylisopropyl)adenosine (PIA, 0.1 μM)) also decreased the response to 1 nM AVP in the MCT. The addition of an A 1-adenosine antagonist relieved the effect of PIA but did not modify the inhibition observed with PGE 2. Thus PGE 2 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.