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 smooth muscle cells (VSMCs), NTG is denitrated to form nitric oxide (NO), which 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 would be increased activity of the cGMP phosphodiesterase (PDE), which decreases cGMP levels. Methods and Results To test this hypothesis, rats were made tolerant by continuous infusion of NTG for 3 days (10 μg · kg−1 · min−1 SC) with an osmotic 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...