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.

KEYWORDS:

• arterioles
• histamine
• retina
• vasoactivity