Gu J W, Brady A L, Anand V, Moore M C, Kelly W C, Adair T H
Department of Physiology and Biophysics, Center for Excellence in Cardiovascular-Renal Research, University of Mississippi Medical Center, Jackson, Mississippi 39216-4505, USA.
Am J Physiol. 1999 Aug;277(2):H595-602. doi: 10.1152/ajpheart.1999.277.2.H595.
We tested whether adenosine has differential effects on vascular endothelial growth factor (VEGF) expression under normoxic and hypoxic conditions, and whether A(1) or A(2) receptors (A(1)R; A(2)R) mediate these effects. Myocardial vascular smooth muscle cells (MVSMCs) from dog coronary artery were exposed to hypoxia (1% O(2)) or normoxia (20% O(2)) in the absence and presence of adenosine agonists or antagonists for 18 h. VEGF protein levels were measured in media with ELISA. VEGF mRNA expression was determined with Northern blot analysis. Under normoxic conditions, the adenosine A(1)R agonists, N(6)-cyclopentyladenosine and R(-)-N(6)-(2-phenylisopropyl)adenosine did not increase VEGF protein levels at A(1)R stimulatory concentrations. However, adenosine (5 microM) and the adenosine A(2)R agonist N(6)-[2-(3, 5-dimethoxyphenyl)-2-(2-methylphenyl)]ethyl adenosine (DPMA; 100 nM) increased VEGF protein levels by 51 and 132% and increased VEGF mRNA expression by 44 and 90%, respectively, in cultured MVSMCs under normoxic conditions. Hypoxia caused an approximately fourfold increase in VEGF protein and mRNA expression, which could not be augmented with exogenous adenosine, A(2)R agonist (DPMA), or A(1)R agonist [1,3-diethyl-8-phenylxanthine (DPX)]. The A(2)R antagonist 8-(3-chlorostyryl)-caffeine completely blocked adenosine-induced VEGF protein and mRNA expression and decreased baseline VEGF protein levels by up to approximately 60% under normoxic conditions but only by approximately 25% under hypoxic conditions. The A(1)R antagonist DPX had no effect. These results are consistent with the hypothesis that 1) adenosine increases VEGF protein and mRNA expression by way of A(2)R. 2) Adenosine plays a major role as an autocrine factor regulating VEGF expression during normoxic conditions but has a relatively minor role during hypoxic conditions. 3) Endogenous adenosine can account for the majority of basal VEGF secretion by MVSMCs under normoxic conditions and could therefore be a maintenance factor for the vasculature.
我们测试了腺苷在常氧和低氧条件下对血管内皮生长因子（VEGF）表达是否具有不同影响，以及A(1)或A(2)受体（A(1)R；A(2)R）是否介导这些作用。将犬冠状动脉的心肌血管平滑肌细胞（MVSMC）在不存在和存在腺苷激动剂或拮抗剂的情况下分别暴露于低氧（1% O₂）或常氧（20% O₂）环境中18小时。用ELISA法检测培养基中的VEGF蛋白水平。用Northern印迹分析确定VEGF mRNA表达。在常氧条件下，腺苷A(1)R激动剂N(6)-环戊基腺苷和R(-)-N(6)-(2-苯异丙基)腺苷在A(1)R刺激浓度下未增加VEGF蛋白水平。然而，在常氧条件下培养的MVSMC中，腺苷（5 microM）和腺苷A(2)R激动剂N(6)-[2-(3,5-二甲氧基苯基)-2-(2-甲基苯基)]乙基腺苷（DPMA；100 nM）分别使VEGF蛋白水平增加了51%和132%，使VEGF mRNA表达增加了44%和90%。低氧使VEGF蛋白和mRNA表达增加约四倍，外源性腺苷、A(2)R激动剂（DPMA）或A(1)R激动剂[1,3-二乙基-8-苯基黄嘌呤（DPX）]均不能使其进一步增加。A(2)R拮抗剂8-(3-氯苯乙烯基)-咖啡因完全阻断了腺苷诱导的VEGF蛋白和mRNA表达，并在常氧条件下使基线VEGF蛋白水平降低多达约60%，但在低氧条件下仅降低约25%。A(1)R拮抗剂DPX没有作用。这些结果与以下假设一致：1）腺苷通过A(2)R增加VEGF蛋白和mRNA表达。2）腺苷在常氧条件下作为调节VEGF表达的自分泌因子起主要作用，但在低氧条件下起相对较小的作用。3）内源性腺苷可占常氧条件下MVSMC基础VEGF分泌的大部分，因此可能是脉管系统的维持因子。
