title: The dilating effect of histamine on pial arteries of cats and its mediation by H2 receptors.
abstract: We studied the effect of histamine and H1 or H2 blockers on the diameter of pial arteries (39-227 micron) using microapplication into the perivascular space. Concentration-response curves for histamine showed dilations which started at 10(-7) M and were maximal at 10(-5) and 10(-4) M. The H2 blocker, cimetidine, induced no vascular reaction over the whole concentration range tested (10(-7) to 10(-3) M). The H1 blocker, mepyramine, was not vasoactive in the concentration range from 10(-7) to 5 X 10(-5) M and evoked dilations at higher concentrations. The concentration-response curve for histamine was only slightly displaced by 10(-5) M mepyramine but was significantly shifted to the right by 10(-5) M cimetidine. The dilating effect of histamine could be reduced in a stepwise manner by increasing concentrations of cimetidine. These findings are in accordance with a selective antagonism between histamine and cimetidine at the H2 receptors of smooth muscle cells of pial arteries. The insignificant role of H1 receptors in histamine-induced dilations is supported by the finding that a combination of H1 and H2 blockers resulted in the same reduction of histamine-induced dilation as did the application of the H2 blocker.
mesh_terms: D000818:Animals; D001158:Arteries / Q000187:drug effects; D002415:Cats; D002927:Cimetidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006632:Histamine / Q000494:pharmacology*; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D008297:Male; D010841:Pia Mater / Q000098:blood supply*; D011738:Pyrilamine / Q000494:pharmacology; D011968:Receptors, Histamine / Q000378:metabolism*; D011970:Receptors, Histamine H2 / Q000378:metabolism*
chemical_list: D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D011968:Receptors, Histamine; D011970:Receptors, Histamine H2; D002927:Cimetidine; D006632:Histamine; D011738:Pyrilamine