Interaction of Peptides Present in Perivascular Nerves on the Smooth Muscle of Cat Cerebral Arteries and on the Stimulation‐evoked Efflux of 3h‐noradrenaline

Studies have been performed using isolated segments of the middle cerebral artery of the cat to determine whether noradrenaline (NA), neuropeptide Y (NPY), avian pancreatic polypeptide (APP), substance P (SP), vasoactive intestinal polypeptide (VIP) and gastrin releasing peptide (GRP) have effects that involve pre- and/or postsynaptic mechanisms. NA, clonidine, NPY and APP produced concentration-dependent contractions of cerebral artery segments, whereas SP and VIP induced relaxation of prostaglandin F2 alpha-contracted arteries. GRP, in the concentrations tested, (up to 2 X 10(-7)M) had no vasomotor activity. The alpha 2-adrenoreceptor agonist clonidine (10(-8) and 10(-6)M) produced a reduction in the field stimulation-evoked release of 3H-NA previously incorporated into the noradrenergic transmitter pool of the arteries, whereas the alpha 2-adrenoreceptor antagonist rauwolscine (10(-8) and 10(-6)M) resulted in increases in 3H-NA release. However, none of the peptides caused any significant change of the stimulation-evoked fractional release of 3H-NA. The results suggest that NPY, APP, SP and VIP have postjunctional effects in cat cerebral arteries and, in the concentrations tested do not affect stimulation-evoked NA release.