Norepinephrine upregulates vascular endothelial growth factor in rat cardiac myocytes by a paracrine mechanism

Norepinephrine has growth-promoting effects in cardiac myocytes. The present study in cultured neonatal rat cardiac myocytes tested the hypothesis that norepinephrine also stimulates expression of vascular endothelial growth factor (VEGF), an important angiogenic factor. As assessed by polymerase chain reaction cardiac myocytes and non-myocytes expressed all three isoforms of rat VEGF, with the short isoform (VEGF121) preferentially expressed in non-myocytes. When cardiac myocytes were stimulated with 1 μM norepinephrine for 24 h in the presence or absence of the specific α- and β-adrenoceptor antagonists prazosin and propranolol, respectively, VEGF mRNA levels and splice variant pattern did not change, whereas atrial natriuretic peptide mRNA levels increased 3 to 4-fold. CoCl2 increased VEGF mRNA levels in cardiac myocytes five-fold. When cardiac myocytes were cultured with conditioned medium from non-myocytes that had been stimulated with norepinephrine for 24 h VEGF mRNA increased 2-fold. The increase was blocked by antibodies neutralizing TGFβ. These data suggest that norepinephrine stimulates myocardial angiogenesis by a paracrine mechanism that involves cardiac non-myocytes and TGFβ.