Upregulation of phosphodiesterase 1A1 expression is associated with the development of nitrate tolerance

Background-The efficacy of nitroglycerin (NTG) as a vasodilator is limited by tolerance, which develops shortly after treatment begins. In vascular sm ooth muscle cells (VSMCs), NTG is denitrated to form nitric oxide (NO), whi ch activates guanylyl cyclase and generates cGMP. cGMP plays a key role in nitrate-induced vasodilation by reducing intracellular Ca2+ concentration. Therefore, one possible mechanism for development of nitrate tolerance woul d be increased activity of the cGMP phosphodiesterase (PDE), which decrease s cGMP levels. Methods and Results-To test this hypothesis, rats were made tolerant by con tinuous infusion of NTG for 3 days (10 mug. kg(-1) . min(-1) SC) with an os motic pump. Analysis of PDE activities showed an increased function of Ca2/calmodulin (CaM)-stimulated PDE (PDE1A1), which preferentially hydrolyzes cGMP after NTG treatment. Western blot analysis for the Ca2+/CaM-stimulated PDE revealed that PDE1A1 was increased 2.3-fold in NTG-tolerant rat aortas . Increased PDE1A1 was due to mRNA upregulation as measured by relative qua ntitative reverse transcription-polymerase chain reaction. The PDE1-specifi c inhibitor vinpocetine partially restored the sensitivity of the tolerant vasculature to subsequent NTG exposure. In cultured rat aortic VSMCs, angio tensin II (Ang II) increased PDE1A1 activity, and vinpocetine blocked the e ffect of Ang II on decrease in cGMP accumulation. Conclusions-Induction of PDE1A1 in nitrate-tolerant vessels may be one mech anism by which NO/cGMP-mediated vasodilation is desensitized and Ca2+-media ted vasoconstriction is supersensitized. Inhibiting PDE1A1 expression and/o r activity could be a novel therapeutic approach to limit nitrate tolerance .