Adenosine upregulates VEGF expression in cultured myocardial vascular smooth muscle cells

We tested whether adenosine has differential effects on vascular endothelia l growth factor (VEGF) expression under normoxic and hypoxic conditions, an d whether A(1) or A(2) receptors (A(1)R; A(2)R) mediate these effects. Myoc ardial 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 presen ce of adenosine agonists or antagonists for 18 h. VEGF protein levels were measured in media with ELISA. VEQF mRNA expression was determined with Nort hern blot analysis. Under normoxic conditions, the adenosine A(1)R agonists , N-6-cyclopentyladenosine and R(-)-N-6-(2-phenylisopropyl)adenosine did no t increase VEGF protein levels at A(1)R stimulatory concentrations. However , adenosine (5 mu M) and the adenosine A(2)R agonist N-6-[2-(3,5-dimethoxyp henyl)-2-(2-methylphenyl)]ethyl adenosine (DPMA; 100 nM) increased VEGF pro tein 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, wh ich 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 prot ein and mRNA expression and decreased baseline VEGF protein levels by up to similar to 60% under normoxic conditions but only by similar to 25% under hypoxic conditions. The A(1)R antagonist DPX had no effect. These results a re 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 adenos ine can account for the majority of basal VEGF secretion by MVSMCs under no rmoxic conditions and could therefore be a maintenance factor for the vascu lature.