Central effects of vasoactive intestinal polypeptide on intraocular pressure and body temperature in rabbits

Administration of vasoactive intestinal polypeptide (VIP) into the rabbit third ventricle via a permanently placed cannula resulted in a dose-dependent increase in intraocular pressure (IOP). IOP was elevated 5.2 mmHg 30 minutes after VIP (10 micrograms/100 microliter) administration. Tonographic outflow facility was not altered by VIP. Thirty minutes after VIP injection into the third ventricle, aqueous humor flow estimated using the Goldmann equation was increased 36% over baseline levels. Intravenous administration of a 10 micrograms dose of VIP did not alter IOP. Systemic blood pressure was unaltered after third ventricle VIP. Systemic pretreatment with the cholinergic antagonist atropine blocked the VIP-induced elevation in IOP. Topical atropine pretreatment had no effect suggesting a central cholinergic mechanism for the VIP-induced increase in IOP. Physiological antagonism of the VIP response was observed after systemic pretreatment with propranolol, phentolamine, or acetazolamide. Body temperature (BT) was significantly elevated in a dose-dependent manner following central VIP administration. Indomethacin pretreatment which had no effect on the IOP response, blocked the VIP temperature response.