[The effect of vasoactive intestinal polypeptide on the eye (authors transl)]

Vasoactive intestinal polypeptide (VIP), in doses of 1, 3, 5, 10 and 30 micrograms dissolved in 10 microliters of physiologic saline, was injected into the anterior chamber of albino rabbit eyes, which had been pretreated with topical 0.5 percent indomethacin. While the blood pressure remained unchanged, the intraocular pressure (IOP) began to rise shortly after injection and reached a maximum in about 20 minutes. An evident dose-response relationship was established between the percentage IOP increase and the dose of VIP. The protein content of the aqueous humor also increased in a dose-dependent manner, and the increases in the IOP and protein content could be significantly correlated. The pupil diameter did not change significantly during the experiments. The sphincter and dilator muscle strips were dissected from the iris of the albino rabbit eye pretreated with 0.5 percent topical indomethacin and incubated in Krebs-Ringer's solution to which VIP was added. A dose-dependent relaxation was induced in the sphincter muscle strip under contraction by 10(-6) M carbachol and also in the dilator muscle under contraction by 3 x 10(-5) M phenylephrine. The ED50 was calculated to be 1.78 x 0.49 x 10(-8) M for the former and 1.91 +/- 0.44 x 10(-9) M (Mean +/- s.e.m.) for the latter muscle strip.