Perivascular peptides relax cerebral arteries concomitant with stimulation of cyclic adenosine monophosphate accumulation or release of an endothelium-derived relaxing factor in the cat.

Calcitonin gene-related peptide (CGRP), substance P (SP) and vasoactive intestinal polypeptide (VIP) have been proposed to be neurotransmitters/neuromodulators in cerebral perivascular nerve fibers. Here, we present pharmacological and biochemical evidence showing that these peptides have different modes of relaxing cerebral blood vessels in the cat. CGRP causes pronounced relaxation, this occurs simultaneously with stimulation of cyclic adenosine monophosphate (cAMP) accumulation. The strong VIP-induced dilatation is parallelled by cAMP accumulation, albeit of a lower magnitude than with CGRP. The SP-induced relaxation was much weaker than that of CGRP and VIP, and it was not associated with cAMP accumulation. Only at concentrations of SP where maximum relaxation had occurred, was a nonsignificant cAMP accumulation seen. The responses to SP and acetylcholine were absent in arteries where the endothelium had been removed, whereas the relaxations induced by CGRP and VIP persisted.