PACAP-27 AND PACAP-38 - VASCULAR EFFECTS IN THE EYE AND SOME OTHER TISSUES IN THE RABBIT

The effects of pituitary adenylate cyclase activating polypeptide (PAC AP) on regional blood flow in the eye and other tissues were investiga ted in albino rabbits. Direct determination of the flow from a cannula ted vortex vein, in animals pretreated with a vasopressin receptor ant agonist, showed that i.v. infusion of either PACAP-27 or PACAP-38 caus ed a dose-dependent (0.08-0.64 pmol/kg per min) decrease in the uveal vascular resistance. Regional blood flow was determined, with radioact ive microspheres, during i.v. infusion of PACAP-27 or PACAP-38 (0.64 p mol/kg per min) in rabbits pretreated with hexamethonium and a vasopre ssin receptor antagonist. In these experiments, both PACAP-27 and PACA P-38 increased choroidal blood flow by about 50%, whereas there was no effect in the anterior uvea. Nor was there any major effect on blood flow in the anterior uvea after intracameral injection of PACAP-27 or PACAP-38 (3 pmol). The largest blood flow increases, caused by i.v. in fusion of PACAP-27 or PACAP-38, were observed in the parotid gland, su bmandibular gland, eyelids and nictitating membrane. Local blood flow in the choroid plexus, pineal gland, posterior pituitary gland, stomac h, kidney and adrenal gland was also significantly increased during th e i.v. infusion of PACAP-27. The results of the present investigation indicate that PACAP-27 and PACAP-38 are about 100 times more potent th an vasoactive intestinal polypeptide and peptide histidine isoleucine as vasodilators in the rabbit choroid and, possibly, also in many othe r tissues of the rabbit.