NEUROPEPTIDE-Y ANALOG WITH SELECTIVE ANTAGONISM OF EFFECTS MEDIATED BY POSTJUNCTIONAL Y-1 RECEPTORS

Neuropeptide, a 36 amino acid peptide, is one of the most ubiquitous neuropeptides in the nervous system. It is released during stimulation of sympathetic nerves and is implicated as an important neurotransmitter regulating cardiovascular activity. Administration of neuropeptide Y results in vasoconstriction and inhibition of neurotransmitter release. However, the absence of any effective inhibitors of neuropeptide Y action have precluded the examination of its possible role in hypertension. Here we describe a synthetic hexapeptide (BRC 672), corresponding to residues 22-27 of neuropeptide Y. Following the administration of BRC 672 (6.7 mu mol/kg), neuropeptide Y-induced presser responses were reduced by 32-48% in a dose-dependent fashion. The inhibition was specific for neuropeptide Y, as the presser response to phenylephrine, an alpha-adrenoceptor agonist, was unchanged. It was selective for the postsynaptic (neuropeptide Y Y-1 receptor-mediated) vasoconstrictor activity, because the presynaptic (neuropeptide Y Y-2 receptor-mediated) cardiac vagal inhibition evoked by injection of neuropeptide Y to rats was not affected. The hexapeptide inhibited the neuropeptide Y-induced increase in cytosolic free Ca2+ in mammalian cells expressing the cloned human neuropeptide Y Y-1 receptor. Injections of BRC 672 significantly reduced blood pressure in anaesthetised rats and in conscious spontaneously hypertensive rats. Resting arterial blood pressure decreased from 136 +/- 4 mm Hg to to 122 +/- 3 mm Hg and remained depressed 2 h after the administration of the hexapeptide in anaesthetised rats. In spontaneously hypertensive rats blood pressure was decreased for up to 4 h.