Synthesis and characterization of a selective peptide antagonist of neuropeptide Y vascular postsynaptic receptors

1 A cyclic dimeric nonapeptide neuropeptide Y (NPY) receptor antagonist, 1229U91, was synthesized by Fmoc chemistry and dimerised in solution. Its effects were assayed in mesenteric arteries from rats and mice, and in rat vas deferens. 2 Mesenteric arteries were cannulated and pressurised to 55 mmHg and the external diameters continuously measured. NPY, PYY, Leu(31)Pro(34)Npy and NPY(13-36) each caused concentration-related contractions with the order of potency PYY greater than or equal to Leu(31)Pro(34)NPY = NPY > NPY (13-36), consistent with the Y-1 receptor subtype. 3 1229U91 had no agonist activity in the arteries but caused a concentration-related rightward shift of NPY (mouse arteries) or Leu(31)Pro(34)NPY (rat) concentration-response curves. The antagonism was competitive with pK(B)s of 7.69+/-0.15 and 7.47+/-0.13 in the mouse and rat arteries, respectively. 4 Sympathetic nerves in the vas deferens were stimulated with a single electrical field pulse every 20 s and the twitch responses recorded. NPY, PW, Leu(31)Pro(34)NPY and NPY (13-36) inhibited the twitches with the order of potency PYY>NPY>NPY(13-36)>>Leu(31)Pro(34)NPY, consistent with the Y-2 receptor subtype. 5 1229U91 inhibited the vas deferens twitch with a shallow concentration-response curve and a timecourse of inhibition distinct from that of NPY. 1229U91 (30 mu M) did not cause a rightward shift of the NPY concentration-response curve. 1229U91 is at least 5 orders of magnitude less potent in the vas deferens than in rat brain Y-2 binding assays reported by others, suggesting that the brain and vas deferens Y-2 receptors are different. 6 It is concluded that 1229U91 is a competitive antagonist of NPY Y-1 vascular receptors and has additional properties that inhibit the electrically evoked twitch of the rat vas deferens.