TRANSIENT CEREBRAL VASODILATORY EFFECT OF NEUROPEPTIDE-Y MEDIATED BY NITRIC-OXIDE

The effects of intracarotidly injected neuropeptide Y (NPY; 0.1 mug/kg ) on the local cerebral blood volume (CBV) and blood flow (CBF) in the parieto-temporal cortex were examined by the photoelectric method in 17 anesthetized cats. CBV reflects the cumulative crosssectional area of the cerebral microvascular beds. NPY immediately caused transient b ut significant increases in CBV and CBF, which lasted for less than 5 min. Thereafter, CBV returned to and remained at the control level, al though CBF was decreased by 30-40% for 60 min during the monitoring pe riod. The CBV increases after NPY were prevented by a 15-min preinject ion of 0.35 mg/kg/min of N(G)-monomethyl-L-arginine (L-NMMA), which is a competitive blocker of nitric oxide synthesis. The CBV increases af ter NPY reappeared following a 15-min administration of 0.25 mg/kg/min of L-arginine, which is a precursor of nitric oxide. We conclude that NPY administered in vivo exerts a previously unreported effect of tra nsient vasodilatation on the cerebral microvessels. This action appear s to be mediated by nitric oxide, which is a major candidate as an end othelium-derived relaxing factor (EDRF).