INTERACTION OF PEPTIDES PRESENT IN PERIVASCULAR NERVES ON THE SMOOTH MUSCLE OF CAT CEREBRAL ARTERIES AND ON THE STIMULATION‐EVOKED EFFLUX OF 3H‐NORADRENALINE

Abstract

Isolated segments of the middle cerebral artery of the cat were used to determine whether noradrenaline (NA [norepinephrine]), 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 .times. 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. None of the peptides caused any significant change of the stimulation-evoked fractional release of 3H-NA. Apparently, NPY, APP, SP, and VIP have postjunctional effects in cat cerebral arteries and, in the concentrations tested, do not affect stimulation-evoked NA release.