Enhancement by histamine of vascular endothelial growth factor production in granulation tissue via H₂ receptors

1 Roles of histamine in the production of vascular endothelial growth factor (VEGF) in the carrageenin-induced granulation tissue in rats were analysed in vitro and in vivo. 2 Incubation of the minced granulation tissue in the presence of histamine (1 and 10 μM) increased the content of VEGF protein in the conditioned medium in a time- and concentration-dependent manner. The levels of VEGF mRNA in the minced granulation tissue were also increased by histamine in a concentration-dependent manner. 3 The increase in the content of VEGF protein in the conditioned medium by histamine (10 μM) was suppressed by the H₂ receptor antagonist cimetidine (IC₅₀ 0.37 μM), but not by the H₁ receptor antagonist pyrilamine maleate, the H₃ receptor antagonist thioperamide or the cyclo-oxygenase inhibitor indomethacin. 4 The histamine-induced increase in the content of VEGF protein in the conditioned medium was inhibited by the cyclic AMP antagonist Rp-cAMP (IC₅₀ 6.8 μM), and the protein kinase A inhibitor H-89 (IC₅₀ 12.5 μM), but not by the protein kinase C inhibitors Ro 31-8425 and calphostin C or the tyrosine kinase inhibitor genistein. 5 Simultaneous injection of cimetidine (400 μg) and indomethacin (100 μg) into the air pouch of rats additively reduced the carrageenin-induced increase in VEGF protein levels and angiogenesis in the granulation tissue as assessed by using carmine dye. 6 These findings indicate that histamine has an activity to induce VEGF production in the granulation tissue via the H₂ receptor-cyclic AMP-protein kinase A pathway and augments angiogenesis in the granulation tissue.