title: Altered arachidonic acid metabolism contributes to the failure of dopamine to inhibit Na+,K(+)-ATPase in kidney of spontaneously hypertensive rats.
abstract: Dopamine decreases tubular sodium reabsorption in part by inhibition of Na+,K(+)-ATPase activity in renal proximal tubules. The signaling mechanism involved in dopamine-mediated inhibition of Na+,K(+)-ATPase is known to be defective in spontaneously hypertensive animals. The present study was designed to evaluate the role of phospholipase A2 (PLA2) and its metabolic pathway in dopamine-induced inhibition of Na+,K(+)-ATPase in renal proximal tubules from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Renal proximal tubular suspensions were prepared and Na+,K(+)-ATPase activity was measured as ouabain-sensitive adenosine triphosphate hydrolysis. Dopamine inhibited Na+,K(+)-ATPase activity in a concentration (1 nM-10 microM)-dependent manner in WKY rats while it failed to inhibit the enzyme activity in SHR. Dopamine (10 microM)-induced inhibition of Na+,K(+)-ATPase activity in WKY rats was significantly blocked by mepacrine (10 microM), a PLA2 inhibitor, suggesting the involvement of PLA2 in dopamine-mediated inhibition of Na+,K(+)-ATPase. Arachidonic acid (a product released by PLA2 action) inhibited Na+,K(+)-ATPase in a concentration-dependent (1-100 microM) manner in WKY rats while the inhibition in SHR was significantly attenuated (IC50: 7.5 and 80 microM in WKY rats and SHR, respectively). Furthermore, lower concentrations of arachidonic acid stimulated (30% at 1 microM) Na+,K(+)-ATPase activity in SHR. This suggests a defect in the metabolism of arachidonic acid in SHR. Proadifen (10 microM), an inhibitor of cytochrome P-450 monoxygenase (an arachidonic acid metabolizing enzyme) significantly blocked the inhibition produced by arachidonic acid in WKY rats and abolished the difference in arachidonic acid inhibition of Na+,K(+)-ATPase between WKY rats and SHR. These data suggest that PLA2 is involved in dopamine-induced inhibition of Na+,K(+)-ATPase and altered arachidonic acid metabolism may contribute to reduced dopaminergic inhibition of Na+,K(+)-ATPase activity in spontaneously hypertensive rats.
authors.affiliation: Institute for Cardiovascular Studies, College of Pharmacy, University of Houston, TX 77204-5511, USA.
authors.forename: T
authors.initials: T
authors.lastname: Hussain
authors.forename: M F
authors.initials: MF
authors.lastname: Lokhandwala
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007668:Kidney / Q000378:metabolism*; D008297:Male; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D016718:Arachidonic Acid; D010741:Phospholipases A; D054467:Phospholipases A2; D000254:Sodium-Potassium-Exchanging ATPase; D004298:Dopamine