Pituitary adenylate cyclase-activating polypeptide- and VIP-induced activation of adenylate cyclase in the porcine non-pigmented ciliary epithelium: effects of antagonists.

Vasoactive intestinal polypeptide (VIP) and two pituitary adenylate cyclase-activating polypeptides (PACAP-38 and PACAP-27) were investigated for their ability to activate the adenylate cyclase system in membrane preparations from the porcine non-pigmented ciliary epithelium (NPE). The NPE was dissociated from the adjacent pigmented ciliary epithelium of the iris-ciliary body (ICB) by incubation in low Ca2+ Ringer's solution. All three peptides caused a dose-dependent increase in cAMP formation in the NPE and the remaining part of the ICE. A VIP antagonist had a small effect on the dose-response curve for VIP, while the two PACAP fragments, PACAP(6-38) and PACAP(6-31), caused a rightward shift of the concentration response curves for PACAP-38, PACAP-27 and VIP. The results of the present study indicate that the non-pigmented ciliary epithelium of the porcine eye contain receptors for PACAP-and VIP-coupled to adenylate cyclase activation.