Vasoactive intestinal peptide (VIP) like peptides in the cerebral circulation of the cat

The present study was designed to study the localization and effects of some VIP-related peptides on the cerebral circulation in cats. A rich supply of nerve fibres containing vasoactive intestinal peptide- (VIP) was seen. Nerve fibres containing pituitary adenylate cyclase activating peptide and helospectin-like immunoreactivity (-IR) were moderate in numbers whereas only a sparse supply of fibres containing helodermin-IR was seen. Double immunostaining revealed that the majority of PACAP- and helospectin-IR nerve fibres contained VIP. Using a sensitive in vitro system prostaglandin F2 alpha-precontracted circular segments of the cat middle cerebral artery relaxed upon administration of VIP, PACAP, helospectin I, helospectin II and helodermin. These effects were non-endothelium dependent with pD2-values varying between 7.6 and 8.1. The maximum relaxation varied between 47% and 79% of precontraction. Local cerebral blood flow was studied in anaesthetised cats. Cortical injection of PACAP-38, helospectin or helodermin, 5 micrograms in a volume of 1 microliter, revealed moderate and consistent increases in flow. The increase in cerebral blood flow was rapid and concentration-dependent with maximum increases of 18 +/- 6% for PACAP, 21 +/- 5% for helodermin, 16 +/- 7% for helospectin I and 19 +/- 5% for helospectin II. The vehicle caused no significant response (2 +/- 4%).