| Abstract: | The action of neuropeptide Y (NPY), which coexists with noradrenaline (NA) in perivascular sympathetic nerves, has been examined on feline cerebrovascular smooth muscle using a sensitive in vitro system. The direct cerebrovascular responses of peptides with structural similarities with NPY, peptide YY (PYY), avian (APP), and bovine (BPP) and human (HPP) pancreatic polypeptides, have been compared with that of NPY on isolated feline cerebral arteries. The relative potency for contractions induced by the peptides is: NPY, PYY greater than APP greater than BPP, HPP. The alpha-adrenoceptor antagonist rauwolscine, which blocked the response to noradrenaline (NA), had no effect on NPY-induced contractions. Neuropeptide Y significantly potentiated contractions induced by 10(-6) M NA, but not by 10(-5) M. Withdrawal of Ca2+ from the extracellular medium for 30 min reduced the contractile response to NPY in cerebral vessels by about 80%. Subsequent readdition of Ca2+ caused reproducible contractions which were inhibited by the calcium entry blocker nimodipine. Nimodipine also relaxed isolated middle cerebral artery segments contracted by NPY and NA in a concentration-dependent manner. The data suggest that NPY mediates contraction of cerebrovascular smooth muscle via a mechanism that is dependent on the concentration of extracellular calcium. |
