Department of Pharmaceutical Sciences, North Dakota State University, Fargo, 58108-6050, USA.
Am J Physiol Heart Circ Physiol. 2012 Dec 15;303(12):H1418-25. doi: 10.1152/ajpheart.00211.2012. Epub 2012 Oct 19.
Melatonin inhibits nitric oxide (NO)-induced relaxation of coronary arteries. We tested the hypothesis that melatonin increases the phosphorylation of phosphodiesterase 5 (PDE5), which increases the activity of the enzyme and thereby decreases intracellular cGMP accumulation in response to NO and inhibits NO-induced relaxation. Sodium nitroprusside (SNP) and 8-Br-cGMP caused concentration-dependent relaxation of isolated coronary arteries suspended in organ chambers for isometric tension recording. In the presence of melatonin, the concentration-response curve to SNP, but not 8-Br-cGMP, was shifted to the right. The effect of melatonin on SNP-induced relaxation was abolished in the presence of the PDE5 inhibitors zaprinast and sildenafil. Melatonin markedly inhibited the SNP-induced increase in intracellular cGMP in coronary arteries, an effect that was also abolished by zaprinast. Treatment of coronary arteries with melatonin caused a nearly fourfold increase in the phosphorylation of PDE5, which increased the catalytic activity of the enzyme and thereby increased the degradation of cGMP to inactive 5'-GMP. Melatonin-induced PDE5 phosphorylation was markedly attenuated in the presence of the PKG1 inhibitors DT-2 or Rp-8-Br-PET-cGMPS and in those arteries in which PKG1 expression was first downregulated by 24-h incubation with SNP before exposure to melatonin. The selective MT(2) receptor antagonist 4-phenyl-2-propionamidotetralin completely blocked the stimulatory effect of melatonin on PDE5 phosphorylation as well as the inhibitory effect of melatonin on SNP-induced relaxation and intracellular cGMP. Thus, in coronary arteries, melatonin acts via MT(2) receptors and PKG1 to increase PDE5 phosphorylation, resulting in decreased cGMP accumulation in response to NO and impaired NO-induced vasorelaxation.
褪黑素抑制一氧化氮（NO）诱导的冠状动脉舒张。我们检验了这样一个假设，即褪黑素增加磷酸二酯酶 5（PDE5）的磷酸化，从而增加酶的活性，进而减少细胞内 cGMP 的积累，以响应 NO 并抑制 NO 诱导的舒张。硝普钠（SNP）和 8-Br-cGMP 引起离体冠状动脉在器官室中悬浮以进行等长张力记录时产生浓度依赖性舒张。在褪黑素存在的情况下，SNP 的浓度-反应曲线向右移位，但 8-Br-cGMP 则不然。PDE5 抑制剂扎普司特和西地那非的存在消除了褪黑素对 SNP 诱导松弛的影响。褪黑素显著抑制 SNP 诱导的冠状动脉内 cGMP 增加，这种作用也被扎普司特消除。用褪黑素处理冠状动脉会导致 PDE5 的磷酸化增加近四倍，这增加了酶的催化活性，从而增加 cGMP 向无活性的 5'-GMP 的降解。PKG1 抑制剂 DT-2 或 Rp-8-Br-PET-cGMPS 的存在以及 SNP 孵育 24 小时后再暴露于褪黑素会导致 PKG1 表达下调，从而显著减弱了 SNP 诱导的 PDE5 磷酸化。选择性 MT(2) 受体拮抗剂 4-苯基-2-丙酰胺四氢呋喃完全阻断了褪黑素对 PDE5 磷酸化的刺激作用，以及褪黑素对 SNP 诱导的舒张和细胞内 cGMP 的抑制作用。因此，在冠状动脉中，褪黑素通过 MT(2) 受体和 PKG1 作用增加 PDE5 磷酸化，导致对 NO 的 cGMP 积累减少和 NO 诱导的血管舒张受损。
