P2Y₂ receptor-stimulated release of prostaglandin E₂ by rat inner medullary collecting duct preparations

Extracellular nucleotides, acting through the P2Y₂ receptor and the associated phosphoinositide-Ca²⁺ signaling pathway, inhibit AVP-stimulated osmotic water permeability in rat inner medullary collecting duct (IMCD). Because a rise in intracellular Ca²⁺ is frequently associated with enhanced arachidonic acid metabolism, we examined the effect of activation of the P2Y₂ receptor on release of PGE₂ in freshly prepared rat IMCD suspensions. Unstimulated IMCD released moderate, but significant, amounts of PGE₂, which were more sensitive to cyclooxygenase (COX)-2 than COX-1 inhibition. Agonist activation of P2Y ₂ receptor by adenosine 5′-O-(3-thiotriphosphate) enhanced release of PGE₂ from IMCD in a time- and concentration-dependent fashion. Purinergic-stimulated release of PGE₂ was completely blocked by nonspecific COX inhibitors (flurbiprofen and 2-acetoxyphenylhept-2-ynyl sulfide). Differential COX inhibition studies revealed that purinergic-stimulated release of PGE₂ was more sensitive to a COX-1-specific inhibitor (valeroyl salicylate) than a COX-2-specific inhibitor (NS-398). Thus purinergic stimulation resulted in significantly more release of PGE₂ in the presence of COX-2 inhibitor than COX-1 inhibitor. If it is assumed that increased release of PGE₂ is related to its increased production, our results suggest that purinergic stimulation of IMCD results in enhanced production and release of PGE₂ in a COX-1-dependent fashion. Because PGE₂ is known to affect transport of water, salt, and urea in IMCD, interaction of the purinergic system with the prostanoid system in IMCD can modulate handling of water, salt, and urea by IMCD and, thus, may constitute an AVP-independent regulatory mechanism.