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.