Histamine Induces Opposing Vasoactive Effects at Different Levels of the Ocular Vasculature

Abstract

Purpose: To characterize the vasoactive properties and receptors of histamine in porcine retinal arterioles compared to that in the long posterior ciliary artery. Methods: Isolated perfused porcine retinal arterioles were used to study vessel diameter in response to histamine (10−10 to 10−4 M). Ring segments from the long posterior ciliary artery were used to study contractile force in response to histamine. Results: Histamine-induced vasodilatation in pig retinal arterioles but contraction in the long posterior ciliary artery. In retinal arterioles, the involvement of H2 receptors was implied by the attenuation of the histamine response in the presence of cimetidine. Further attenuation of the histamine response by pyrilamine suggests the involvement of H1 receptors. In retinal arterioles denuded of endothelial cells, the histamine response was only slightly reduced.Conclusion: Histamine induces opposing vasoactive effects at different levels of the porcine ocular vasculature.