Vasorelaxant effect of PACAP-27 on canine cerebral arteries and rat intracerebral arterioles

Abstract

The vasorelaxant effects of pituitary adenylate cyclase activating polypeptide (PACAP)-27 were examined and compared with those of PACAP-38 and vasoactive intestinal polypeptide (VIP) on isolated canine cerebral arteries and rat intracerebral arterioles in vitro. The addition of PACAP-27, PACAP-38 or VIP resulted in similar concentration-dependent relaxations in both canine basilar arteries and rat intracerebral arterioles. There were regional differences in the PACAP-27-induced relaxations measured in canine cerebral arteries. The maximum relaxation induced by PACAP-27 was significantly lower in the basilar arteries (23.0 ± 5.6%) than in the rostrally located arteries (proximal middle cerebral arteries: 45.4 ± 5.7%, anterior cerebral arteries: 55.2 ± 5.8%). The maximum relaxation induced by PACAP-27 in the basilar arteries was significantly enhanced by mechanical removal of the endothelium (16.4 ± 4.5% vs. 32.7 ± 5.8%) as well as by pretreatment with indomethacin or aspirin (12.9 ± 4.1% vs. 48.7 ± 6.1% and 46.5 ± 9.2%, respectively). Incubation of canine cerebral arteries with PACAP-27 in vitro resulted in an increased release of prostaglandin F 2α in the buffer from 14.5 ± 2.1 pg/min/1 mg vessel to 31.1 ± 4.2 pg/min/1 mg vessel, while other cyclooxygenase cascade metabolites such as prostaglandin E 2, thromboxane B 2 and 6-keto prostaglandin F 1α did not change. These data suggest that the PACAP-27-induced relaxation of canine basilar arteries may be associated with prostaglandin F 2α or its precursor, prostaglandin H 2.