Vasoactive intestinal polypeptide (VIP)-immunoreactive nerve fibers in the anterior uvea of the guinea pig.

The presence of vasoactive intestinal polypeptide (VIP)-like immunoreactivity, especially in the anterior part of the guinea pig uvea, was studied using an indirect immunofluorescence technique. In the ciliary body, thin varicose VIP fibers displaying VIP immunoreactivity were observed in the ciliary muscle and in the ciliary processes. The iris was virtually free of VIP fibers. In the choroid, VIP-immunoreactive fibers were seen mainly in close association with the choroidal blood vessels. The histochemical localization of VIP-immunoreactive fibers in the anterior uvea suggests that the physiological role of neuronal VIP in the uvea is not only associated with the regulation of the blood flow of the choroid but also with the functions of ciliary muscle and ciliary epithelium.