PACAP, a VIP-like peptide: immunohistochemical localization and effect upon cat pial arteries and cerebral blood flow

Pituitary adenylate cyclase activating peptide (PACAP) is a vasoactive intestinal polypeptide (VIP)-like peptide recently isolated from ovine hypothalami. Nerve fibers containing PACAP immunoreactivity were present in the adventitia and the adventitia-media border of cat cerebral arteries. Double immunostaining revealed that PACAP-immunoreactive nerve fibers constituted a subpopulation of the VIP-containing fibers. PACAP effected a concentration-dependent relaxation of feline middle cerebral arteries that had been precontracted with prostaglandin F2 alpha. The maximum relaxation, 24 and 34% of precontraction, was achieved with PACAP-38 and PACAP-27, respectively, at a concentration of 10(-6) M. In cats anesthetized with alpha-chloralose, intracerebral microinjection of PACAP effected a moderate increase in cerebral blood flow. The maximal increase (18.6 +/- 6%) was observed following the injection of 5 micrograms PACAP.