Stimulation of angiogenesis by substance P and interleukin‐1 in the rat and its inhibition by NK1 or interleukin‐1 receptor antagonists

1 Daily administration of 1 nmol substance P or 3 pmol recombinant human interleukin‐1 alpha (IL‐1α) caused intense neovascularization in a rat sponge model of angiogenesis. Lower doses of substance P (10 pmol) or IL‐1α (0.3 pmol) were ineffective when given alone. When combined at these low doses, substance P and IL‐1α interacted to produce an enhanced neovascular response. 2 By use of selective tachykinin NK1, NK2 and NK3 receptor agonists, ([Sar9,Met(O2)11]substance P, [β‐Ala8]neurokinin A(4–10), Succ‐[Asp6,MePhe8]substance P(6–11) (senktide), respectively), it was established that the activation of NK1 receptors is most likely to mediate the angiogenic response to substance P in this model. 3 The angiogenic activity of substance P and IL‐1α (10 pmol and 0.3 pmol day−1, respectively) was abolished by co‐administration of (i) the selective peptide NK1 receptor antagonist, L‐668,169 (1 nmol day−1), (ii) the selective non‐peptide NK1 receptor antagonists, RP 67580 and (±)‐CP‐96,345 (both at 1 nmol day−1) or (iii) the IL‐1 receptor antagonist, IL‐1ra, (50 μg day−1). In contrast, the selective NK2 receptor antagonist, L‐659,874 (1 nmol day−1) was ineffective. 4 The angiogenic action of substance P and IL‐1α was resistant to modification by mepyramine (1 nmol day−1) and/or cimetidine (10 nmol day−1), indomethacin (7 nmol day−1) or the platelet‐activating factor (PAF) antagonist, WEB‐2086 (22 nmol day−1), indicating that histamine, prostaglandins and PAF are not likely to be involved in this neovascular response. 5 The inhibition of the substance P/IL‐1 angiogenic response by selective NK1 receptor antagonists or by an IL‐1 receptor antagonist demonstrates that angiosuppression can be achieved by blocking the activity of angiogenic factors at the receptor level.