CHARACTERIZATION OF HISTAMINE-RECEPTORS IN CAT CEREBRAL-ARTERIES INVITRO AND INSITU

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  • 1 January 1983
    • journal article
    • research article
    • Vol. 225  (1) , 168-175
Abstract
Histamine is probably a mediator of vascular responses in the brain, but there is little experimental evidence for its importance in this role. By using both in vitro and in situ techniques responses of cat pial arteries to stimulation of histamine receptors by pharmacological agents were studied. In vitro, histamine and 2,2-pyridylethylamine (PEA, H1 agonist) caused contraction of resting arteries while impromidine (H2 agonist) was without effect. The PEA-induced constriction was blocked by the histamine H1 antagonist, mepyramine. When the arteries were precontracted (by 3 .times. 10-6 M prostaglandin F2.alpha.), all 3 agents caused vascular relaxation with an order of effectiveness histamine = impromidine .mchgt. PEA. The responses of histamine and impromidine were reduced by the H2-antagonist, metiamide or cimetidine. Schild plots for the H2 receptor antagonists resulted in pA2 [competitive antagonistic activity] values of 6.90 and 7.03 for metiamide and cimetidine, respectively. In situ, neither agonist caused pial arterial constriction. Impromidine was considerably more effective than PEA in producing arterial dilatation. Metiamide reduced the effect of impromidine, whereas the dilatation of PEA was reduced by mepyramine. Dilatations resulting from PEA persisted in the presence of metiamide. Evidently, histamine H2 receptors are present in cerebral vascular smooth muscle as identified both in vitro and in situ. Indications for the additional presence of H1 receptors are weak.