title: Histamine induces opposing vasoactive effects at different levels of the ocular vasculature.
abstract: OBJECTIVE
  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 H(2) 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.
  
  
  CONCLUSIONS
  Histamine induces opposing vasoactive effects at different levels of the porcine ocular vasculature.
authors.affiliation: Centre for Ophthalmology and Visual Science, The University of Western Australia, Perth, Western Australia.
authors.forename: Er
authors.initials: E
authors.lastname: Su
authors.forename: Dao
authors.initials: D
authors.lastname: Yu
authors.forename: Stephen
authors.initials: S
authors.lastname: Cringle
mesh_terms: D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000502:physiology; D019842:Ciliary Arteries / Q000187:drug effects / Q000502:physiology*; D004730:Endothelium, Vascular / Q000502:physiology; D006632:Histamine / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D011969:Receptors, Histamine H1 / Q000502:physiology; D011970:Receptors, Histamine H2 / Q000502:physiology; D012161:Retinal Artery / Q000187:drug effects / Q000502:physiology*; D013552:Swine; D014664:Vasodilation / Q000502:physiology*
chemical_list: D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D006632:Histamine