Histamine and serotonin induce angiogenesis in vivo. (A) Female, 4-to 5-week Nu/Nu mice were implanted subcutaneously with control pellets or pellets that contained indicated amounts of histamine or serotonin. Tissues were dissected and photographed 3 days later. (B) Tissues adjacent to pellet implant sites were immunostained with an antibody against CD31. Mean vessel density was calculated with Image J software as described in “Methods” (n = 10 from 4 animals per group). ***P < .001, Student t test. (C) Effect of various histamine and serotonin receptor antagonists on angiogenesis induced in Nu/Nu mice by histamine- or serotonin-releasing pellets. Inhibitors (1mg/kg) were injected intraperitoneally daily, beginning when the pellets were implanted; in addition, a single injection of inhibitor (1 micromole in 50 μl or HBSS as control) was administered intradermally daily directly over the pellet implant site. Tissues were harvested and photographed on day 6. Histamine-induced angiogenesis was strongly inhibited by 1H and H2 antagonists but not by an antagonist of H4. Serotonin-induced angiogenesis was strongly inhibited by an antagonist of serotonin receptor types 2 and 3, but not by antagonists of types 1, 6, and 7. SU1498, an inhibitor of VEGFR-2, had no effect on angiogenesis induced by either histamine or serotonin. Data are representative of 8 mice in each group.
